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  • How to force iscsi initiator to login only once

    - by Disco
    Trying to setup a few CentOS nodes to connect to a Dell MD3600i array, i'm running into the issue that the MD3600i shows 4 different portals (with different IP addresses) and when i launch the initiator on host side well, it connects to every IP address it has seen during the discovery phase; resulting in duplicates. How can I 'force' the initiator to discard every other IP and let me choose only one IP portal to connect to ? Must be damn stupid but I can't figure out how. Thx

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  • In TCP/IP terms, how does a download speed limiter in an office work?

    - by TessellatingHeckler
    Assume an office of people, they want to limit HTTP downloads to a max of 40% bandwidth of their internet connection speed so that it doesn't block other traffic. We say "it's not supported in your firewall", and they say the inevitable line "we used to be able to do it with our Netgear/DLink/DrayTek". Thinking about it, a download is like this: HTTP GET request Server sends file data as TCP packets Client acknowledges receipt of TCP packets Repeat until download finished. The speed is determined by how fast the server sends data to you, and how fast you acknowledge it. So, to limit download speed, you have two choices: 1) Instruct the server to send data to you more slowly - and I don't think there's any protocol feature to request that in TCP or HTTP. 2) Acknowledge packets more slowly by limiting your upload speed, and also ruin your upload speed. How do devices do this limiting? Is there a standard way?

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  • Corosync :: Restarting some resources after Lan connectivity issue

    - by moebius_eye
    I am currently looking into corosync to build a two-node cluster. So, I've got it working fine, and it does what I want to do, which is: Lost connectivity between the two nodes gives the first node '10node' both Failover Wan IPs. (aka resources WanCluster100 and WanCluster101 ) '11node' does nothing. He "thinks" he still has his Failover Wan IP. (aka WanCluster101) But it doesn't do this: '11node' should restart the WanCluster101 resource when the connectivity with the other node is back. This is to prevent a condition where node10 simply dies (and thus does not get 11node's Failover Wan IP), resulting in a situation where none of the nodes have 10node's failover IP because 10node is down 11node has "given back" his failover Wan IP. Here's the current configuration I'm working on. node 10sch \ attributes standby="off" node 11sch \ attributes standby="off" primitive LanCluster100 ocf:heartbeat:IPaddr2 \ params ip="172.25.0.100" cidr_netmask="32" nic="eth3" \ op monitor interval="10s" \ meta is-managed="true" target-role="Started" primitive LanCluster101 ocf:heartbeat:IPaddr2 \ params ip="172.25.0.101" cidr_netmask="32" nic="eth3" \ op monitor interval="10s" \ meta is-managed="true" target-role="Started" primitive Ping100 ocf:pacemaker:ping \ params host_list="192.0.2.1" multiplier="500" dampen="15s" \ op monitor interval="5s" \ meta target-role="Started" primitive Ping101 ocf:pacemaker:ping \ params host_list="192.0.2.1" multiplier="500" dampen="15s" \ op monitor interval="5s" \ meta target-role="Started" primitive WanCluster100 ocf:heartbeat:IPaddr2 \ params ip="192.0.2.100" cidr_netmask="32" nic="eth2" \ op monitor interval="10s" \ meta target-role="Started" primitive WanCluster101 ocf:heartbeat:IPaddr2 \ params ip="192.0.2.101" cidr_netmask="32" nic="eth2" \ op monitor interval="10s" \ meta target-role="Started" primitive Website0 ocf:heartbeat:apache \ params configfile="/etc/apache2/apache2.conf" options="-DSSL" \ operations $id="Website-one" \ op start interval="0" timeout="40" \ op stop interval="0" timeout="60" \ op monitor interval="10" timeout="120" start-delay="0" statusurl="http://127.0.0.1/server-status/" \ meta target-role="Started" primitive Website1 ocf:heartbeat:apache \ params configfile="/etc/apache2/apache2.conf.1" options="-DSSL" \ operations $id="Website-two" \ op start interval="0" timeout="40" \ op stop interval="0" timeout="60" \ op monitor interval="10" timeout="120" start-delay="0" statusurl="http://127.0.0.1/server-status/" \ meta target-role="Started" group All100 WanCluster100 LanCluster100 group All101 WanCluster101 LanCluster101 location AlwaysPing100WithNode10 Ping100 \ rule $id="AlWaysPing100WithNode10-rule" inf: #uname eq 10sch location AlwaysPing101WithNode11 Ping101 \ rule $id="AlWaysPing101WithNode11-rule" inf: #uname eq 11sch location NeverLan100WithNode11 LanCluster100 \ rule $id="RAND1083308" -inf: #uname eq 11sch location NeverPing100WithNode11 Ping100 \ rule $id="NeverPing100WithNode11-rule" -inf: #uname eq 11sch location NeverPing101WithNode10 Ping101 \ rule $id="NeverPing101WithNode10-rule" -inf: #uname eq 10sch location Website0NeedsConnectivity Website0 \ rule $id="Website0NeedsConnectivity-rule" -inf: not_defined pingd or pingd lte 0 location Website1NeedsConnectivity Website1 \ rule $id="Website1NeedsConnectivity-rule" -inf: not_defined pingd or pingd lte 0 colocation Never -inf: LanCluster101 LanCluster100 colocation Never2 -inf: WanCluster100 LanCluster101 colocation NeverBothWebsitesTogether -inf: Website0 Website1 property $id="cib-bootstrap-options" \ dc-version="1.1.7-ee0730e13d124c3d58f00016c3376a1de5323cff" \ cluster-infrastructure="openais" \ expected-quorum-votes="2" \ no-quorum-policy="ignore" \ stonith-enabled="false" \ last-lrm-refresh="1408954702" \ maintenance-mode="false" rsc_defaults $id="rsc-options" \ resource-stickiness="100" \ migration-threshold="3" I also have a less important question concerning this line: colocation NeverBothLans -inf: LanCluster101 LanCluster100 How do I tell it that this collocation only applies to '11node'.

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  • WSUS is not using Akamai CDN for syncronisation source

    - by Geekman
    I've just installed a WSUS onto our network, and I'm currently doing the initial sync. I've found that WSUS does not seem to be talking to an Akamai cache, but rather with MS directly. This is contrary to what I've always thought regarding Windows Update traffic. Tcpdump of our WSUS server doing initial sync... As you can see it's speaking with 65.55.194.221. For me to speak to this IP, I have to go over international transit links. Which is of course not ideal. 8:42:31.279757 IP 65.55.194.221.https > XXXX.XXXX.XXXX.XXXX.50888: Flags [.], seq 4379374:4380834, ack 289611, win 256, length 1460 18:42:31.279759 IP 65.55.194.221.https > XXXX.XXXX.XXXX.XXXX.50888: Flags [.], seq 4380834:4382294, ack 289611, win 256, length 1460 18:42:31.279762 IP 65.55.194.221.https > XXXX.XXXX.XXXX.XXXX.50888: Flags [.], seq 4382294:4383754, ack 289611, win 256, length 1460 18:42:31.279764 IP 65.55.194.221.https > XXXX.XXXX.XXXX.XXXX.50888: Flags [P.], seq 4383754:4384144, ack 289611, win 256, length 390 18:42:31.279793 IP XXXX.XXXX.XXXX.XXXX.50888 > 65.55.194.221.https: Flags [.], ack 4369154, win 23884, length 0 18:42:31.279888 IP XXXX.XXXX.XXXX.XXXX.50888 > 65.55.194.221.https: Flags [.], ack 4377914, win 23884, length 0 18:42:31.280015 IP XXXX.XXXX.XXXX.XXXX.50888 > 65.55.194.221.https: Flags [.], ack 4384144, win 23884, length 0 And yet, if I ping download.windowsupdate.com it seems to resolve to a local (national) Akamai node, just fine: root@some-node:~# ping download.windowsupdate.com PING a26.ms.akamai.net (210.9.88.48) 56(84) bytes of data. 64 bytes from a210-9-88-48.deploy.akamaitechnologies.com (210.9.88.48): icmp_req=1 ttl=59 time=1.02 ms 64 bytes from a210-9-88-48.deploy.akamaitechnologies.com (210.9.88.48): icmp_req=2 ttl=59 time=1.10 ms Why is this? And how can I change that (if possible)? I know that I can manually specify a WSUS source to sync with instead of pick the default MS Update like I currently have... But it seems like I shouldn't have to do this. NOTE: I've haven't confirmed if a WUA speaks with Akamai, just looking at WSUS as all WUAs will use our internal WSUS from now on. We'll be looking to join an IX shortly with the hopes of peering with an Akamai cache and have very fast access to Windows Updates. Before I let this drive my motivations for an IX at all I want to first confirm it's actually possible for WSUS to speak with an Akamai cache. I know this is somewhat networking related, but I feel like it has more to do with WSUS than anything, so someone who knows WSUS better than me will likely be able to figure this out.

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  • What are some good, IP Address Management solutions for IPv6? [closed]

    - by Russell Heilling
    There are a number of open source IPAM tools available for IPv4 address management; however there seems to be a distinct lack of actively updated tools available for IPv6. Other than FreeIPdb (code no longer maintained) or the RIPE Database (I have seen some customisations to the RIPEdb that allow for enterprise/ISP IPAM but it seems like overkill for a system that will probably only ever handle one /32 worth of space). Are there any other options that I'm missing? (Database only please. I know vi can be used for flat text IPAM, that's how I'm handling our /32 at the moment, but I don't see it scaling for much longer) It doesn't have to be open source but what are folks doing to manage IPv6 in a dual stack environment

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  • dig @my-server-ip mydomain.com works from inside, not from outside?

    - by x4954
    My server has 2 ips: x.x.x.73 and x.x.x.248. I can access my site via these ips, using Web browser. {Now, from a CentOS machine (not my server), using terminal} If I: dig @x.x.x.73 mydomain.com dig @x.x.x.248 mydomain.com I get the result: Connection timed out; no server could be reached. Could somebody please tell me how to fix it? Thank you. More information: If I log in to my server using ssh and do: dig @x.x.x.73 mydomain.com dig @x.x.x.248 mydomain.com I can see my zone shown as expected: ; <<>> DiG 9.3.6-P1-RedHat-9.3.6-16.P1.el5_7.1 <<>> @x.x.x.73 mydomain.com ; (1 server found) ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12757 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 2 ;; QUESTION SECTION: ;mydomain.com. IN A ;; ANSWER SECTION: mydomain.com. 38400 IN A x.x.x.73 mydomain.com. 38400 IN A x.x.x.248 ;; AUTHORITY SECTION: mydomain.com. 38400 IN NS ns2.mydomain.com. mydomain.com. 38400 IN NS ns1.mydomain.com. ;; ADDITIONAL SECTION: ns1.mydomain.com. 38400 IN A x.x.x.73 ns2.mydomain.com. 38400 IN A x.x.x.248 ;; Query time: 20 msec ;; SERVER: x.x.x.73#53(x.x.x.73) ;; WHEN: Sun Jan 15 11:46:30 2012 ;; MSG SIZE rcvd: 129 BIND version 9.3.6, Centos 5. Logging to my server using ssh, do inga "dig google.com" also shows expected results.

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  • Group traffic shaping with traffic control?

    - by mmcbro
    I'm trying to limit the output bandwidth generated by an application with linux tc. This application sends me the source port of the request that I use has a filter to limit each user at a given downloadspeed. I feel that my setup could be managed way better if I had a better knowledge of linux tc. At the application level users are categorized as members of a group, each group have a limited bandwidth. Example : Members of group A : 512kbit/s Members of group B : 1Mbit/s Members of group C : 2Mbit/s When a user connects to the application, it retrieves the source port to the origin of the request from the user and sends me the source port and the bandwidth at which the user must be limited depending on group to which it belongs. With these informations I must add the appropriate rules so that the user (the source port in reality) is limited to the right bandwidth. If the user that connect isn't a member of any group it should be limited at a default bandwidth speed. I'm actually managing this by using a self made daemon that add or remove rules from when it receive a request from the application. With my little knowledge of tc I'm not able to limit other users (ones that aren't in a group, all others in fact) at a default speed and my configuration seems awful to me. Here is the base of my tc qdisc and classes : tc qdisc add dev eth0 root handle 1: htb tc class add dev eth0 parent 1: classid 1:1 htb rate 100mbps ceil 125mbps To classify a user at a given speed I have to add one subclass and then associate one filter to it : # a member of group A tc class add dev eth0 parent 1:1 classid 1:11 htb rate 512kbps ceil 512kbps # tts associated filter to match his source port tc filter add dev eth0 protocol ip parent 1:0 prio 1 u32 match ip sport 50001 flowid 1:11 # a member of group A again tc class add dev eth0 parent 1:1 classid 1:12 htb rate 512kbps ceil 512kbps # tts associated filter to match his source port tc filter add dev eth0 protocol ip parent 1:0 prio 1 u32 match ip sport 61524 flowid 1:12 # a member of group B again tc class add dev eth0 parent 1:1 classid 1:13 htb rate 1000kbps ceil 1000kbps # tts associated filter to match his source port tc filter add dev eth0 protocol ip parent 1:0 prio 1 u32 match ip sport 57200 flowid 1:13 I already know that a source port could be the same if its coming from a different IP address the thing is the application is behind a proxy so I don't have to manage any IP address in that situation. I would like to know how to manage the fact that for all other users (request/source port, whatever you name it) could be limited at a given speed each. I mean that each connection should be able to use at max 100kbit/s for example, not a shared 100kbit/s. I also would like to know if there is a way to simplify my rules. I don't know if it is possible to use only one class per group and associate multiple filters to the same class so each users could be handled by one class and not one class per user. I appreciate any advice, thanks.

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  • <VirtualHost fqdn.mydomain.com:80> not recommended?

    - by Alois Mahdal
    In Apache2 documentation thay say that in <VirtualHost *:80>, the * can be replaced by IP or FQDN, but the FQDN is not recommended. Addr can be: The IP address of the virtual host; A fully qualified domain name for the IP address of the virtual host (not recommended); But why is it not recommended? If I have www.mydomain.com and webmail.mydomain.com pointing to the same IP address, why shouldn't I use the names here?

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  • Thin web server - single or multiple instances per IP address:port?

    - by wchrisjohnson
    I'm deploying a rack/sinatra/web socket app onto several servers and will use thin as the web server (http://code.macournoyer.com/thin/). There are almost no views to show, so I am not front-ending it with a traditional web server like Apache or nginx. In general, you see thin started and the underlying config file for it has the number of server instances to start, say 3, and the port to start with, say 5000. So, in my example, when thin starts, it starts up three instances on a range of ports, starting on port 5000. If I have a series of virtual machines, say 3, 6, 9, etc. that I treat as a cluster, would/should I choose to start a single thin instance on each VM, or multiple instances on each VM? Why? Thanks - Chris

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  • Router behind Router--second router (and its clients) cannot be "seen" even after both routers are D

    - by Trioke
    Couple of terminology I guess I should get out of the way for consistency's sake throughout the post: External Router/Modem - SMC 8014WG - External IP 173.32.144.134 - Internal IP 192.168.0.1 Internal Router - LinkSys WRT120N - "External" IP of 192.168.0.175 - Internal IP 192.168.1.1 - Connected via Ethernet Cable (a really long one, from the basement to the second floor) PC - IP 192.168.200 - Connected Wirelessly via WAP2 Personal. Laptop - Used to try and diagnose the problem, a 4th machine to the setup which won't be part of the final setup once everything works. The actual problem: I've tried setting the LinkySys router as a DMZ'd client on the SMC router, and then DMZ'd the actual PC on the LinkSys. So the DMZ looks like this: On the SMZ, client with IP 192.168.0.175 is DMZ'd. On the LinkSys, client with IP 192.168.1.200 is DMZ'd. No dice. I then tried port forwarding the necessary port on the SMC to the LinkSys (lets just say, port 80). Then port forwarded Port 80 on the LinkSys to the PC. Same as the DMZ scenario above, but change DMZ with port forwarding. No dice, still :(. Now here's where I went stupid--and tell me if one should never do this--I enabled both DMZ and port forwarding at the same time. I fired up Opera--my browser of choice ;)--typed in 173.32.144.134:6333 and... ... Third time is the charm they say? Well, clearly not. Otherwise I wouldn't be here ;). To diagnose the problem, I enabled "Allow remote access to the Admin panel" on the LinkSys router, and specified port 6333 as the port to use. I port forwarded port 6333 on the SMC to 192.168.0.175, and access my external IP of 173.32.144.134:6333 in hopes of seeing the Admin panel... No dice (I think I've ran out of dice by now ;)). So to see where the problem was, I connected a laptop to the SMC via LAN cable, and typed in 192.168.0.175:6333, and viola, Admin Panel access! So the problem looks like it lies with the SMC--But that's as far as I've got, I've done the port forwarding, the DMZ'ing, and I've even disabled the built-in firewall for safe measures, but nothing worked. So, here I am. Unable to connect to the PC behind the Internal router externally, and without anything to go on other than to come here and ask for the wisdom of the the superuser folks :). If any more detail is required, just ask. (Apologies in advance, if questions should never be this long winded!)

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  • Why use hosts file?

    - by dK3
    My company has a staging site and we access it by a url like this: www.example.com Until today I did not realise that I had a line in my hosts file which said: 192.0.2.0 www.example.com (the ip is fake here) now when I try to access this site through ip , I cannot get access.. why is this the case? We even own the domain we are using so I do not see the reason why we are using a hosts file and more over, why I cannot access the site through simple IP (by the way, we are using an internal IP)

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  • Traffic going to wrong server

    - by markxi
    I'm in the process of migrating to a new server, but some traffic that should be going to old server is now coming to the new server before I am ready to migrate. My provider used an IP used as the secondary nameserver on the old server as the primary IP on the new server, so now my secondary nameserver is directing traffic to the new server. Is there a way to forward the traffic hitting the new IP back to the old IP while I wait for DNS to propagate? Server is Linux CENTOS 6.5 x86_64 w/ cPanel Thanks

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  • connected ethernet without disabling wireless, now I have *two* LAN ip's?

    - by peter karasev
    Ok I'm on ubuntu 11.04, not too knowledgeable about network stuff. Usually people ask things like "wired works but wireless does not!". In m y case, I'm just curious about what it means to have both of them seemingly connected. In 'ipconfig' in shell I see that I have 192.168.1.2 for the wireless AND 192.168.1.3 for the ethernet. What does this mean for applications, does one of the two get precedence? It seems like my pages load slightly faster, so perhaps the ethernet is being used, but I could be imagining the speedup...

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  • websites resolving in browser but not resolving in CLI. Can ping IP but not domain name (unknown host)

    - by tjkoding
    Hi guys I'm currently developing using rails and for some reason bundle install is returning the following output Error Bundler::HTTPError during request to dependency API Fetching full source index from https://rubygems.org/ Could not reach https://rubygems.org/ I've discovered that pinging by domain name keeps returning an unknown host. The browser is still resolving web pages just fine and I've managed to confirm that the problem is localized (i.e. the rubygems page isn't down). I'm completely lost so any help would be much appreciated. Thanks in advance!

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  • Add elements to Arraylist and it replaces all previous elements in Java

    - by pie154
    I am adding elements to a ArrayList and it adds the first one correctly but then when I add any subsequent elements it wipes replaces the other elements with the value form the most recently added and adds a new element to the ArrayList. I ran test using arraylist and ints and even another created class and it worked perfectly but soemthing about the custon class i am using here causes problems. The code for the array list is public static void main(String args[]){ List<BasicEvent> list = new ArrayList<BasicEvent>(); list.add(new BasicEvent("Basic", "Door", 9, 4444, new Date(12,04,2010), new Time(12,04,21), 1, 0.98, 0)); list.add(new BasicEvent("Composite", "Door", 125, 4444, new Date(12,04,2010), new Time(12,04,20), 1, 0.98, 1)); list.add(new BasicEvent("Basic", "Door", 105, 88, new Date(12,04,2010), new Time(12,05,23), 1, 0.98, 0)); list.add(new BasicEvent("Basic", "Door", 125, 12, new Date(12,04,2010), new Time(12,05,28), 1, 0.98, 1)); list.add(new BasicEvent("Basic", "Door", 129, 25, new Date(12,04,2010), new Time(12,05,30), 1, 0.98, 0)); list.add(new BasicEvent("Basic", "Door", 125, 63, new Date(12,04,2010), new Time(12,04,20), 1, 0.98, 1)); list.add(new BasicEvent("Basic", "Detect", 127, 9, new Date(12,04,2010), new Time(12,05,29), 1, 0.98, -1)); for(int i=0;i<list.size();i++) {System.out.println("list a poition " + i + " is " + BasicEvent.basicToString(list.get(i)));} And the code for the custom class basicEvent is public class BasicEvent { public static String Level; public static String EType; public static double xPos; public static double yPos; public static Date date; public static Time time; public static double Rlb; public static double Sig; public static int Reserved; public BasicEvent(String L, String E, double X, double Y, Date D, Time T, double R, double S, int Res){ Level = L; EType = E; xPos = X; yPos = Y; date = D; time = T; Rlb = R; Sig = S; Reserved = Res; }; public static String basicToString(BasicEvent bse){ String out = bse.getLevel() + ";" + bse.getEtype() + ";" + bse.getxPos() + ";" + bse.getyPos() + ";" + bse.getDate().dateAsString() + ";" + bse.getTime().timeAsString() + ";" + bse.getRlb() + ";" + bse.getSig() + ";" + bse.getReserved(); return out; }

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  • SWIG & Java Use of carrays.i and array_functions for C Array of Strings

    - by c12
    I have the below configuration where I'm trying to create a test C function that returns a pointer to an Array of Strings and then wrap that using SWIG's carrays.i and array_functions so that I can access the Array elements in Java. Uncertainties: %array_functions(char, SWIGArrayUtility); - not sure if char is correct inline char *getCharArray() - not sure if C function signature is correct String result = getCharArray(); - String return seems odd, but that's what is generated by SWIG SWIG.i: %module Test %{ #include "test.h" %} %include <carrays.i> %array_functions(char, SWIGArrayUtility); %include "test.h" %pragma(java) modulecode=%{ public static char[] getCharArrayImpl() { final int num = numFoo(); char ret[] = new char[num]; String result = getCharArray(); for (int i = 0; i < num; ++i) { ret[i] = SWIGArrayUtility_getitem(result, i); } return ret; } %} Inline Header C Function: #ifndef TEST_H #define TEST_H inline static unsigned short numFoo() { return 3; } inline char *getCharArray(){ static char* foo[3]; foo[0]="ABC"; foo[1]="5CDE"; foo[2]="EEE6"; return foo; } #endif Java Main Tester: public class TestMain { public static void main(String[] args) { System.loadLibrary("TestJni"); char[] test = Test.getCharArrayImpl(); System.out.println("length=" + test.length); for(int i=0; i < test.length; i++){ System.out.println(test[i]); } } } Java Main Tester Output: length=3 ? ? , SWIG Generated Java APIs: public class Test { public static String new_SWIGArrayUtility(int nelements) { return TestJNI.new_SWIGArrayUtility(nelements); } public static void delete_SWIGArrayUtility(String ary) { TestJNI.delete_SWIGArrayUtility(ary); } public static char SWIGArrayUtility_getitem(String ary, int index) { return TestJNI.SWIGArrayUtility_getitem(ary, index); } public static void SWIGArrayUtility_setitem(String ary, int index, char value) { TestJNI.SWIGArrayUtility_setitem(ary, index, value); } public static int numFoo() { return TestJNI.numFoo(); } public static String getCharArray() { return TestJNI.getCharArray(); } public static char[] getCharArrayImpl() { final int num = numFoo(); char ret[] = new char[num]; String result = getCharArray(); System.out.println("result=" + result); for (int i = 0; i < num; ++i) { ret[i] = SWIGArrayUtility_getitem(result, i); System.out.println("ret[" + i + "]=" + ret[i]); } return ret; } }

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  • How can I make this client as a multithread client?

    - by Johanna
    Hi, I have read a lot about multithread client but for this one,I can not make it multithread! would you please help me? public class MainClient implements Runnable{ private static InformationClass info = new InformationClass(); private static Socket c; private static String text; public static String getText() { return text; } public static void setText(String text) { MainClient.text = text; } private static PrintWriter os; private static BufferedReader is; static boolean closed = false; /** * @param args the command line arguments */ public static void main(String[] args) { MainFrame farme = new MainFrame(); farme.setVisible(true); try { c = new Socket("localhost", 5050); os = new PrintWriter(c.getOutputStream(), true); is = new BufferedReader(new InputStreamReader(c.getInputStream())); } catch (UnknownHostException ex) { Logger.getLogger(MainClient.class.getName()).log(Level.SEVERE, null, ex); } catch (IOException ex) { Logger.getLogger(MainClient.class.getName()).log(Level.SEVERE, null, ex); } } public static void active() { String teXt = MainClient.getText(); System.out.println(teXt); os.println(teXt); try { String line = is.readLine(); System.out.println("Text received: " + line); os.flush(); is.close(); is.close(); c.close(); } catch (IOException ex) { Logger.getLogger(MainClient.class.getName()).log(Level.SEVERE, null, ex); } } } also active method will be called when the client write something on the text area and then clicks on the send button. 2) also i have a question that: in the other class I have this action performed for my send button,does it mean that client is multithread?? private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { new Thread(new Runnable() { @Override public void run() { // This gets run in a background thread String text = jTextArea1.getText(); jTextArea2.append(client.getCurrentName() + " : " + text + "\n"); MainClient.setText(client.getCurrentName() + " : " + text + "\n"); clear(); MainClient.active(); } }).start(); } Last EDIT: this is my active method: public static void active() { String teXt = MainClient.getText(); os.println(teXt); String line = is.readLine(); System.out.println("Text received: " + line); os.flush(); is.close(); is.close(); c.close(); }

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  • Understanding C# async / await (1) Compilation

    - by Dixin
    Now the async / await keywords are in C#. Just like the async and ! in F#, this new C# feature provides great convenience. There are many nice documents talking about how to use async / await in specific scenarios, like using async methods in ASP.NET 4.5 and in ASP.NET MVC 4, etc. In this article we will look at the real code working behind the syntax sugar. According to MSDN: The async modifier indicates that the method, lambda expression, or anonymous method that it modifies is asynchronous. Since lambda expression / anonymous method will be compiled to normal method, we will focus on normal async method. Preparation First of all, Some helper methods need to make up. internal class HelperMethods { internal static int Method(int arg0, int arg1) { // Do some IO. WebClient client = new WebClient(); Enumerable.Repeat("http://weblogs.asp.net/dixin", 10) .Select(client.DownloadString).ToArray(); int result = arg0 + arg1; return result; } internal static Task<int> MethodTask(int arg0, int arg1) { Task<int> task = new Task<int>(() => Method(arg0, arg1)); task.Start(); // Hot task (started task) should always be returned. return task; } internal static void Before() { } internal static void Continuation1(int arg) { } internal static void Continuation2(int arg) { } } Here Method() is a long running method doing some IO. Then MethodTask() wraps it into a Task and return that Task. Nothing special here. Await something in async method Since MethodTask() returns Task, let’s try to await it: internal class AsyncMethods { internal static async Task<int> MethodAsync(int arg0, int arg1) { int result = await HelperMethods.MethodTask(arg0, arg1); return result; } } Because we used await in the method, async must be put on the method. Now we get the first async method. According to the naming convenience, it is called MethodAsync. Of course a async method can be awaited. So we have a CallMethodAsync() to call MethodAsync(): internal class AsyncMethods { internal static async Task<int> CallMethodAsync(int arg0, int arg1) { int result = await MethodAsync(arg0, arg1); return result; } } After compilation, MethodAsync() and CallMethodAsync() becomes the same logic. This is the code of MethodAsyc(): internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MethodAsync(int arg0, int arg1) { MethodAsyncStateMachine methodAsyncStateMachine = new MethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; methodAsyncStateMachine.Builder.Start(ref methodAsyncStateMachine); return methodAsyncStateMachine.Builder.Task; } } It just creates and starts a state machine MethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Result; private TaskAwaiter<int> awaitor; void IAsyncStateMachine.MoveNext() { try { if (this.State != 0) { this.awaitor = HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaitor.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaitor, ref this); return; } } else { this.State = -1; } this.Result = this.awaitor.GetResult(); } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); return; } this.State = -2; this.Builder.SetResult(this.Result); } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine param0) { this.Builder.SetStateMachine(param0); } } The generated code has been cleaned up so it is readable and can be compiled. Several things can be observed here: The async modifier is gone, which shows, unlike other modifiers (e.g. static), there is no such IL/CLR level “async” stuff. It becomes a AsyncStateMachineAttribute. This is similar to the compilation of extension method. The generated state machine is very similar to the state machine of C# yield syntax sugar. The local variables (arg0, arg1, result) are compiled to fields of the state machine. The real code (await HelperMethods.MethodTask(arg0, arg1)) is compiled into MoveNext(): HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(). CallMethodAsync() will create and start its own state machine CallMethodAsyncStateMachine: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(CallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> CallMethodAsync(int arg0, int arg1) { CallMethodAsyncStateMachine callMethodAsyncStateMachine = new CallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; callMethodAsyncStateMachine.Builder.Start(ref callMethodAsyncStateMachine); return callMethodAsyncStateMachine.Builder.Task; } } CallMethodAsyncStateMachine has the same logic as MethodAsyncStateMachine above. The detail of the state machine will be discussed soon. Now it is clear that: async /await is a C# level syntax sugar. There is no difference to await a async method or a normal method. A method returning Task will be awaitable. State machine and continuation To demonstrate more details in the state machine, a more complex method is created: internal class AsyncMethods { internal static async Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; } } In this method: There are multiple awaits. There are code before the awaits, and continuation code after each await After compilation, this multi-await method becomes the same as above single-await methods: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; multiCallMethodAsyncStateMachine.Builder.Start(ref multiCallMethodAsyncStateMachine); return multiCallMethodAsyncStateMachine.Builder.Task; } } It creates and starts one single state machine, MultiCallMethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Arg2; public int Arg3; public int ResultOfAwait1; public int ResultOfAwait2; public int ResultToReturn; private TaskAwaiter<int> awaiter; void IAsyncStateMachine.MoveNext() { try { switch (this.State) { case -1: HelperMethods.Before(); this.awaiter = AsyncMethods.MethodAsync(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 0: this.ResultOfAwait1 = this.awaiter.GetResult(); HelperMethods.Continuation1(this.ResultOfAwait1); this.awaiter = AsyncMethods.MethodAsync(this.Arg2, this.Arg3).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 1; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 1: this.ResultOfAwait2 = this.awaiter.GetResult(); HelperMethods.Continuation2(this.ResultOfAwait2); this.ResultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; this.State = -2; this.Builder.SetResult(this.ResultToReturn); break; } } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); } } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { this.Builder.SetStateMachine(stateMachine); } } The above code is already cleaned up, but there are still a lot of things. More clean up can be done, and the state machine can be very simple: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { // State: // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End public int State; public TaskCompletionSource<int> ResultToReturn; // int resultToReturn ... public int Arg0; // int Arg0 public int Arg1; // int arg1 public int Arg2; // int arg2 public int Arg3; // int arg3 public int ResultOfAwait1; // int resultOfAwait1 ... public int ResultOfAwait2; // int resultOfAwait2 ... private Task<int> currentTaskToAwait; /// <summary> /// Moves the state machine to its next state. /// </summary> void IAsyncStateMachine.MoveNext() { try { switch (this.State) { // Orginal code is splitted by "case"s: // case -1: // HelperMethods.Before(); // MethodAsync(Arg0, arg1); // case 0: // int resultOfAwait1 = await ... // HelperMethods.Continuation1(resultOfAwait1); // MethodAsync(arg2, arg3); // case 1: // int resultOfAwait2 = await ... // HelperMethods.Continuation2(resultOfAwait2); // int resultToReturn = resultOfAwait1 + resultOfAwait2; // return resultToReturn; case -1: // -1 is begin. HelperMethods.Before(); // Code before 1st await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg0, this.Arg1); // 1st task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 0. this.State = 0; IAsyncStateMachine this1 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => this1.MoveNext()); // Callback break; case 0: // Now 1st await is done. this.ResultOfAwait1 = this.currentTaskToAwait.Result; // Get 1st await's result. HelperMethods.Continuation1(this.ResultOfAwait1); // Code after 1st await and before 2nd await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg2, this.Arg3); // 2nd task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 1. this.State = 1; IAsyncStateMachine this2 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => this2.MoveNext()); // Callback break; case 1: // Now 2nd await is done. this.ResultOfAwait2 = this.currentTaskToAwait.Result; // Get 2nd await's result. HelperMethods.Continuation2(this.ResultOfAwait2); // Code after 2nd await. int resultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; // Code after 2nd await. // End with resultToReturn. this.State = -2; // -2 is end. this.ResultToReturn.SetResult(resultToReturn); break; } } catch (Exception exception) { // End with exception. this.State = -2; // -2 is end. this.ResultToReturn.SetException(exception); } } /// <summary> /// Configures the state machine with a heap-allocated replica. /// </summary> /// <param name="stateMachine">The heap-allocated replica.</param> [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { // No core logic. } } Only Task and TaskCompletionSource are involved in this version. And MultiCallMethodAsync() can be simplified to: [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync_(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, ResultToReturn = new TaskCompletionSource<int>(), // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End State = -1 }; (multiCallMethodAsyncStateMachine as IAsyncStateMachine).MoveNext(); // Original code are in this method. return multiCallMethodAsyncStateMachine.ResultToReturn.Task; } Now the whole state machine becomes very clear - it is about callback: Original code are split into pieces by “await”s, and each piece is put into each “case” in the state machine. Here the 2 awaits split the code into 3 pieces, so there are 3 “case”s. The “piece”s are chained by callback, that is done by Builder.AwaitUnsafeOnCompleted(callback), or currentTaskToAwait.ContinueWith(callback) in the simplified code. A previous “piece” will end with a Task (which is to be awaited), when the task is done, it will callback the next “piece”. The state machine’s state works with the “case”s to ensure the code “piece”s executes one after another. Callback Since it is about callback, the simplification  can go even further – the entire state machine can be completely purged. Now MultiCallMethodAsync() becomes: internal static Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { TaskCompletionSource<int> taskCompletionSource = new TaskCompletionSource<int>(); try { // Oringinal code begins. HelperMethods.Before(); MethodAsync(arg0, arg1).ContinueWith(await1 => { int resultOfAwait1 = await1.Result; HelperMethods.Continuation1(resultOfAwait1); MethodAsync(arg2, arg3).ContinueWith(await2 => { int resultOfAwait2 = await2.Result; HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; // Oringinal code ends. taskCompletionSource.SetResult(resultToReturn); }); }); } catch (Exception exception) { taskCompletionSource.SetException(exception); } return taskCompletionSource.Task; } Please compare with the original async / await code: HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; Yeah that is the magic of C# async / await: Await is literally pretending to wait. In a await expression, a Task object will be return immediately so that caller is not blocked. The continuation code is compiled as that Task’s callback code. When that task is done, continuation code will execute. Please notice that many details inside the state machine are omitted for simplicity, like context caring, etc. If you want to have a detailed picture, please do check out the source code of AsyncTaskMethodBuilder and TaskAwaiter.

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  • Understanding C# async / await (1) Compilation

    - by Dixin
    Now the async / await keywords are in C#. Just like the async and ! in F#, this new C# feature provides great convenience. There are many nice documents talking about how to use async / await in specific scenarios, like using async methods in ASP.NET 4.5 and in ASP.NET MVC 4, etc. In this article we will look at the real code working behind the syntax sugar. According to MSDN: The async modifier indicates that the method, lambda expression, or anonymous method that it modifies is asynchronous. Since lambda expression / anonymous method will be compiled to normal method, we will focus on normal async method. Preparation First of all, Some helper methods need to make up. internal class HelperMethods { internal static int Method(int arg0, int arg1) { // Do some IO. WebClient client = new WebClient(); Enumerable.Repeat("http://weblogs.asp.net/dixin", 10) .Select(client.DownloadString).ToArray(); int result = arg0 + arg1; return result; } internal static Task<int> MethodTask(int arg0, int arg1) { Task<int> task = new Task<int>(() => Method(arg0, arg1)); task.Start(); // Hot task (started task) should always be returned. return task; } internal static void Before() { } internal static void Continuation1(int arg) { } internal static void Continuation2(int arg) { } } Here Method() is a long running method doing some IO. Then MethodTask() wraps it into a Task and return that Task. Nothing special here. Await something in async method Since MethodTask() returns Task, let’s try to await it: internal class AsyncMethods { internal static async Task<int> MethodAsync(int arg0, int arg1) { int result = await HelperMethods.MethodTask(arg0, arg1); return result; } } Because we used await in the method, async must be put on the method. Now we get the first async method. According to the naming convenience, it is named MethodAsync. Of course a async method can be awaited. So we have a CallMethodAsync() to call MethodAsync(): internal class AsyncMethods { internal static async Task<int> CallMethodAsync(int arg0, int arg1) { int result = await MethodAsync(arg0, arg1); return result; } } After compilation, MethodAsync() and CallMethodAsync() becomes the same logic. This is the code of MethodAsyc(): internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MethodAsync(int arg0, int arg1) { MethodAsyncStateMachine methodAsyncStateMachine = new MethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; methodAsyncStateMachine.Builder.Start(ref methodAsyncStateMachine); return methodAsyncStateMachine.Builder.Task; } } It just creates and starts a state machine, MethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Result; private TaskAwaiter<int> awaitor; void IAsyncStateMachine.MoveNext() { try { if (this.State != 0) { this.awaitor = HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaitor.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaitor, ref this); return; } } else { this.State = -1; } this.Result = this.awaitor.GetResult(); } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); return; } this.State = -2; this.Builder.SetResult(this.Result); } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine param0) { this.Builder.SetStateMachine(param0); } } The generated code has been refactored, so it is readable and can be compiled. Several things can be observed here: The async modifier is gone, which shows, unlike other modifiers (e.g. static), there is no such IL/CLR level “async” stuff. It becomes a AsyncStateMachineAttribute. This is similar to the compilation of extension method. The generated state machine is very similar to the state machine of C# yield syntax sugar. The local variables (arg0, arg1, result) are compiled to fields of the state machine. The real code (await HelperMethods.MethodTask(arg0, arg1)) is compiled into MoveNext(): HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(). CallMethodAsync() will create and start its own state machine CallMethodAsyncStateMachine: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(CallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> CallMethodAsync(int arg0, int arg1) { CallMethodAsyncStateMachine callMethodAsyncStateMachine = new CallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; callMethodAsyncStateMachine.Builder.Start(ref callMethodAsyncStateMachine); return callMethodAsyncStateMachine.Builder.Task; } } CallMethodAsyncStateMachine has the same logic as MethodAsyncStateMachine above. The detail of the state machine will be discussed soon. Now it is clear that: async /await is a C# language level syntax sugar. There is no difference to await a async method or a normal method. As long as a method returns Task, it is awaitable. State machine and continuation To demonstrate more details in the state machine, a more complex method is created: internal class AsyncMethods { internal static async Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; } } In this method: There are multiple awaits. There are code before the awaits, and continuation code after each await After compilation, this multi-await method becomes the same as above single-await methods: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; multiCallMethodAsyncStateMachine.Builder.Start(ref multiCallMethodAsyncStateMachine); return multiCallMethodAsyncStateMachine.Builder.Task; } } It creates and starts one single state machine, MultiCallMethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Arg2; public int Arg3; public int ResultOfAwait1; public int ResultOfAwait2; public int ResultToReturn; private TaskAwaiter<int> awaiter; void IAsyncStateMachine.MoveNext() { try { switch (this.State) { case -1: HelperMethods.Before(); this.awaiter = AsyncMethods.MethodAsync(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 0: this.ResultOfAwait1 = this.awaiter.GetResult(); HelperMethods.Continuation1(this.ResultOfAwait1); this.awaiter = AsyncMethods.MethodAsync(this.Arg2, this.Arg3).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 1; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 1: this.ResultOfAwait2 = this.awaiter.GetResult(); HelperMethods.Continuation2(this.ResultOfAwait2); this.ResultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; this.State = -2; this.Builder.SetResult(this.ResultToReturn); break; } } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); } } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { this.Builder.SetStateMachine(stateMachine); } } Once again, the above state machine code is already refactored, but it still has a lot of things. More clean up can be done if we only keep the core logic, and the state machine can become very simple: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { // State: // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End public int State; public TaskCompletionSource<int> ResultToReturn; // int resultToReturn ... public int Arg0; // int Arg0 public int Arg1; // int arg1 public int Arg2; // int arg2 public int Arg3; // int arg3 public int ResultOfAwait1; // int resultOfAwait1 ... public int ResultOfAwait2; // int resultOfAwait2 ... private Task<int> currentTaskToAwait; /// <summary> /// Moves the state machine to its next state. /// </summary> public void MoveNext() // IAsyncStateMachine member. { try { switch (this.State) { // Original code is split by "await"s into "case"s: // case -1: // HelperMethods.Before(); // MethodAsync(Arg0, arg1); // case 0: // int resultOfAwait1 = await ... // HelperMethods.Continuation1(resultOfAwait1); // MethodAsync(arg2, arg3); // case 1: // int resultOfAwait2 = await ... // HelperMethods.Continuation2(resultOfAwait2); // int resultToReturn = resultOfAwait1 + resultOfAwait2; // return resultToReturn; case -1: // -1 is begin. HelperMethods.Before(); // Code before 1st await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg0, this.Arg1); // 1st task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 0. this.State = 0; MultiCallMethodAsyncStateMachine that1 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => that1.MoveNext()); break; case 0: // Now 1st await is done. this.ResultOfAwait1 = this.currentTaskToAwait.Result; // Get 1st await's result. HelperMethods.Continuation1(this.ResultOfAwait1); // Code after 1st await and before 2nd await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg2, this.Arg3); // 2nd task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 1. this.State = 1; MultiCallMethodAsyncStateMachine that2 = this; this.currentTaskToAwait.ContinueWith(_ => that2.MoveNext()); break; case 1: // Now 2nd await is done. this.ResultOfAwait2 = this.currentTaskToAwait.Result; // Get 2nd await's result. HelperMethods.Continuation2(this.ResultOfAwait2); // Code after 2nd await. int resultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; // Code after 2nd await. // End with resultToReturn. this.State = -2; // -2 is end. this.ResultToReturn.SetResult(resultToReturn); break; } } catch (Exception exception) { // End with exception. this.State = -2; // -2 is end. this.ResultToReturn.SetException(exception); } } /// <summary> /// Configures the state machine with a heap-allocated replica. /// </summary> /// <param name="stateMachine">The heap-allocated replica.</param> [DebuggerHidden] public void SetStateMachine(IAsyncStateMachine stateMachine) // IAsyncStateMachine member. { // No core logic. } } Only Task and TaskCompletionSource are involved in this version. And MultiCallMethodAsync() can be simplified to: [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, ResultToReturn = new TaskCompletionSource<int>(), // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End State = -1 }; multiCallMethodAsyncStateMachine.MoveNext(); // Original code are moved into this method. return multiCallMethodAsyncStateMachine.ResultToReturn.Task; } Now the whole state machine becomes very clean - it is about callback: Original code are split into pieces by “await”s, and each piece is put into each “case” in the state machine. Here the 2 awaits split the code into 3 pieces, so there are 3 “case”s. The “piece”s are chained by callback, that is done by Builder.AwaitUnsafeOnCompleted(callback), or currentTaskToAwait.ContinueWith(callback) in the simplified code. A previous “piece” will end with a Task (which is to be awaited), when the task is done, it will callback the next “piece”. The state machine’s state works with the “case”s to ensure the code “piece”s executes one after another. Callback If we focus on the point of callback, the simplification  can go even further – the entire state machine can be completely purged, and we can just keep the code inside MoveNext(). Now MultiCallMethodAsync() becomes: internal static Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { TaskCompletionSource<int> taskCompletionSource = new TaskCompletionSource<int>(); try { // Oringinal code begins. HelperMethods.Before(); MethodAsync(arg0, arg1).ContinueWith(await1 => { int resultOfAwait1 = await1.Result; HelperMethods.Continuation1(resultOfAwait1); MethodAsync(arg2, arg3).ContinueWith(await2 => { int resultOfAwait2 = await2.Result; HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; // Oringinal code ends. taskCompletionSource.SetResult(resultToReturn); }); }); } catch (Exception exception) { taskCompletionSource.SetException(exception); } return taskCompletionSource.Task; } Please compare with the original async / await code: HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; Yeah that is the magic of C# async / await: Await is not to wait. In a await expression, a Task object will be return immediately so that execution is not blocked. The continuation code is compiled as that Task’s callback code. When that task is done, continuation code will execute. Please notice that many details inside the state machine are omitted for simplicity, like context caring, etc. If you want to have a detailed picture, please do check out the source code of AsyncTaskMethodBuilder and TaskAwaiter.

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  • controller path not found for static images? asp.net mvc routing issue?

    - by rksprst
    I have an image folder stored at ~/Content/Images/ I am loading these images via <img src="/Content/Images/Image.png" /> Recently, the images aren't loading and I am getting the following errors in my error log. What's weird is that some images load fine, while others do not load. Anyone have any idea what is wrong with my routes? Am I missing an ignore route for the /Content/ folder? I am also getting the same error for favicon.ico and a bunch of other image files... <Fatal> -- 3/25/2010 2:32:38 AM -- System.Web.HttpException: The controller for path '/Content/Images/box_bottom.png' could not be found or it does not implement IController. at System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(Type controllerType) at System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) at System.Web.Mvc.MvcHandler.ProcessRequest(HttpContextBase httpContext) at System.Web.Mvc.MvcHandler.ProcessRequest(HttpContext httpContext) at System.Web.Mvc.MvcHandler.System.Web.IHttpHandler.ProcessRequest(HttpContext httpContext) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) My current routes look like this: routes.IgnoreRoute("{resource}.axd/{*pathInfo}"); routes.MapRoute( "Default", // Route name "{controller}/{action}/{id}", // URL with parameters new { controller = "Home", action = "Index", id = "" } // Parameter defaults ); routes.MapRoute( "ControllerDefault", // Route name "{controller}/project/{projectid}/{action}/{searchid}", // URL with parameters new { controller = "Listen", action = "Index", searchid = "" } // Parameter defaults ); Thanks!

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  • What makes static initialization functions good, bad, or otherwise?

    - by Richard Levasseur
    Suppose you had code like this: _READERS = None _WRITERS = None def Init(num_readers, reader_params, num_writers, writer_params, ...args...): ...logic... _READERS = new ReaderPool(num_readers, reader_params) _WRITERS = new WriterPool(num_writers, writer_params) ...more logic... class Doer: def __init__(...args...): ... def Read(self, ...args...): c = _READERS.get() try: ...work with conn finally: _READERS.put(c) def Writer(...): ...similar to Read()... To me, this is a bad pattern to follow, some cons: Doers can be created without its preconditions being satisfied The code isn't easily testable because ConnPool can't be directly mocked out. Init has to be called right the first time. If its changed so it can be called multiple times, extra logic has to be added to check if variables are already defined, and lots of NULL values have to be passed around to skip re-initializing. In the event of threads, the above becomes more complicated by adding locking Globals aren't being used to communicate state (which isn't strictly bad, but a code smell) On the other hand, some pros: its very convenient to call Init(5, "user/pass", 2, "user/pass") It simple and "clean" Personally, I think the cons outweigh the pros, that is, testability and assured preconditions outweigh simplicity and convenience.

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