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  • Is it possible to implement bitwise operators using integer arithmetic?

    - by Statement
    Hello World! I am facing a rather peculiar problem. I am working on a compiler for an architecture that doesn't support bitwise operations. However, it handles signed 16 bit integer arithmetics and I was wondering if it would be possible to implement bitwise operations using only: Addition (c = a + b) Subtraction (c = a - b) Division (c = a / b) Multiplication (c = a * b) Modulus (c = a % b) Minimum (c = min(a, b)) Maximum (c = max(a, b)) Comparisons (c = (a < b), c = (a == b), c = (a <= b), et.c.) Jumps (goto, for, et.c.) The bitwise operations I want to be able to support are: Or (c = a | b) And (c = a & b) Xor (c = a ^ b) Left Shift (c = a << b) Right Shift (c = a b) (All integers are signed so this is a problem) Signed Shift (c = a b) One's Complement (a = ~b) (Already found a solution, see below) Normally the problem is the other way around; how to achieve arithmetic optimizations using bitwise hacks. However not in this case. Writable memory is very scarce on this architecture, hence the need for bitwise operations. The bitwise functions themselves should not use a lot of temporary variables. However, constant read-only data & instruction memory is abundant. A side note here also is that jumps and branches are not expensive and all data is readily cached. Jumps cost half the cycles as arithmetic (including load/store) instructions do. On other words, all of the above supported functions cost twice the cycles of a single jump. Some thoughts that might help: I figured out that you can do one's complement (negate bits) with the following code: // Bitwise one's complement b = ~a; // Arithmetic one's complement b = -1 - a; I also remember the old shift hack when dividing with a power of two so the bitwise shift can be expressed as: // Bitwise left shift b = a << 4; // Arithmetic left shift b = a * 16; // 2^4 = 16 // Signed right shift b = a >>> 4; // Arithmetic right shift b = a / 16; For the rest of the bitwise operations I am slightly clueless. I wish the architects of this architecture would have supplied bit-operations. I would also like to know if there is a fast/easy way of computing the power of two (for shift operations) without using a memory data table. A naive solution would be to jump into a field of multiplications: b = 1; switch (a) { case 15: b = b * 2; case 14: b = b * 2; // ... exploting fallthrough (instruction memory is magnitudes larger) case 2: b = b * 2; case 1: b = b * 2; } Or a Set & Jump approach: switch (a) { case 15: b = 32768; break; case 14: b = 16384; break; // ... exploiting the fact that a jump is faster than one additional mul // at the cost of doubling the instruction memory footprint. case 2: b = 4; break; case 1: b = 2; break; }

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  • Javascript Closures - What are the negatives?

    - by vol7ron
    Question: There seem to be many benefits to Closures, but what are the negatives (memory leakage? obfuscation problems? bandwidth increasage?)? Additionally, is my understanding of Closures correct? Finally, once closures are created, can they be destroyed? I've been reading a little bit about Javascript Closures. I hope someone a little more knowledgeable will guide my assertions, correcting me where wrong. Benefits of Closures: Encapsulate the variables to a local scope, by using an internal function. The anonymity of the function is insignificant. What I've found helpful is to do some basic testing, regarding local/global scope: <script type="text/javascript"> var global_text = ""; var global_count = 0; var global_num1 = 10; var global_num2 = 20; var global_num3 = 30; function outerFunc() { var local_count = local_count || 0; alert("global_num1: " + global_num1); // global_num1: undefined var global_num1 = global_num1 || 0; alert("global_num1: " + global_num1); // global_num1: 0 alert("global_num2: " + global_num2); // global_num2: 20 global_num2 = global_num2 || 0; // (notice) no definition with 'var' alert("global_num2: " + global_num2); // global_num2: 20 global_num2 = 0; alert("local_count: " + local_count); // local_count: 0 function output() { global_num3++; alert("local_count: " + local_count + "\n" + "global_count: " + global_count + "\n" + "global_text: " + global_text ); local_count++; } local_count++; global_count++; return output; } var myFunc = outerFunc(); myFunc(); /* Outputs: ********************** * local_count: 1 * global_count: 1 * global_text: **********************/ global_text = "global"; myFunc(); /* Outputs: ********************** * local_count: 2 * global_count: 1 * global_text: global **********************/ var local_count = 100; myFunc(); /* Outputs: ********************** * local_count: 3 * global_count: 1 * global_text: global **********************/ alert("global_num1: " + global_num1); // global_num1: 10 alert("global_num2: " + global_num2); // global_num2: 0 alert("global_num3: " + global_num3); // global_num3: 33 </script> Interesting things I took out of it: The alerts in outerFunc are only called once, which is when the outerFunc call is assigned to myFunc (myFunc = outerFunc()). This assignment seems to keep the outerFunc open, in what I would like to call a persistent state. Everytime myFunc is called, the return is executed. In this case, the return is the internal function. Something really interesting is the localization that occurs when defining local variables. Notice the difference in the first alert between global_num1 and global_num2, even before the variable is trying to be created, global_num1 is considered undefined because the 'var' was used to signify a local variable to that function. -- This has been talked about before, in the order of operation for the Javascript engine, it's just nice to see this put to work. Globals can still be used, but local variables will override them. Notice before the third myFunc call, a global variable called local_count is created, but it as no effect on the internal function, which has a variable that goes by the same name. Conversely, each function call has the ability to modify global variables, as noticed by global_var3. Post Thoughts: Even though the code is straightforward, it is cluttered by alerts for you guys, so you can plug and play. I know there are other examples of closures, many of which use anonymous functions in combination with looping structures, but I think this is good for a 101-starter course to see the effects. The one thing I'm concerned with is the negative impact closures will have on memory. Because it keeps the function environment open, it is also keeping those variables stored in memory, which may/may not have performance implications, especially regarding DOM traversals and garbage collection. I'm also not sure what kind of role this will play in terms of memory leakage and I'm not sure if the closure can be removed from memory by a simple "delete myFunc;." Hope this helps someone, vol7ron

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  • Random Complete System Unresponsiveness Running Mathematical Functions

    - by Computer Guru
    I have a program that loads a file (anywhere from 10MB to 5GB) a chunk at a time (ReadFile), and for each chunk performs a set of mathematical operations (basically calculates the hash). After calculating the hash, it stores info about the chunk in an STL map (basically <chunkID, hash>) and then writes the chunk itself to another file (WriteFile). That's all it does. This program will cause certain PCs to choke and die. The mouse begins to stutter, the task manager takes 2 min to show, ctrl+alt+del is unresponsive, running programs are slow.... the works. I've done literally everything I can think of to optimize the program, and have triple-checked all objects. What I've done: Tried different (less intensive) hashing algorithms. Switched all allocations to nedmalloc instead of the default new operator Switched from stl::map to unordered_set, found the performance to still be abysmal, so I switched again to Google's dense_hash_map. Converted all objects to store pointers to objects instead of the objects themselves. Caching all Read and Write operations. Instead of reading a 16k chunk of the file and performing the math on it, I read 4MB into a buffer and read 16k chunks from there instead. Same for all write operations - they are coalesced into 4MB blocks before being written to disk. Run extensive profiling with Visual Studio 2010, AMD Code Analyst, and perfmon. Set the thread priority to THREAD_MODE_BACKGROUND_BEGIN Set the thread priority to THREAD_PRIORITY_IDLE Added a Sleep(100) call after every loop. Even after all this, the application still results in a system-wide hang on certain machines under certain circumstances. Perfmon and Process Explorer show minimal CPU usage (with the sleep), no constant reads/writes from disk, few hard pagefaults (and only ~30k pagefaults in the lifetime of the application on a 5GB input file), little virtual memory (never more than 150MB), no leaked handles, no memory leaks. The machines I've tested it on run Windows XP - Windows 7, x86 and x64 versions included. None have less than 2GB RAM, though the problem is always exacerbated under lower memory conditions. I'm at a loss as to what to do next. I don't know what's causing it - I'm torn between CPU or Memory as the culprit. CPU because without the sleep and under different thread priorities the system performances changes noticeably. Memory because there's a huge difference in how often the issue occurs when using unordered_set vs Google's dense_hash_map. What's really weird? Obviously, the NT kernel design is supposed to prevent this sort of behavior from ever occurring (a user-mode application driving the system to this sort of extreme poor performance!?)..... but when I compile the code and run it on OS X or Linux (it's fairly standard C++ throughout) it performs excellently even on poor machines with little RAM and weaker CPUs. What am I supposed to do next? How do I know what the hell it is that Windows is doing behind the scenes that's killing system performance, when all the indicators are that the application itself isn't doing anything extreme? Any advice would be most welcome.

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  • Annotate over Multi-table Inheritance in Django

    - by user341584
    I have a base LoggedEvent model and a number of subclass models like follows: class LoggedEvent(models.Model): user = models.ForeignKey(User, blank=True, null=True) timestamp = models.DateTimeField(auto_now_add=True) class AuthEvent(LoggedEvent): good = models.BooleanField() username = models.CharField(max_length=12) class LDAPSearchEvent(LoggedEvent): type = models.CharField(max_length=12) query = models.CharField(max_length=24) class PRISearchEvent(LoggedEvent): type = models.CharField(max_length=12) query = models.CharField(max_length=24) Users generate these events as they do the related actions. I am attempting to generate a usage-report of how many of each event-type each user has caused in the last month. I am struggling with Django's ORM and while I am close I am running into a problem. Here is the query code: ef usage(request): # Calculate date range today = datetime.date.today() month_start = datetime.date(year=today.year, month=today.month - 1, day=1) month_end = datetime.date(year=today.year, month=today.month, day=1) - datetime.timedelta(days=1) # Search for how many LDAP events were generated per user, last month baseusage = User.objects.filter(loggedevent__timestamp__gte=month_start, loggedevent__timestamp__lte=month_end) ldapusage = baseusage.exclude(loggedevent__ldapsearchevent__id__lt=1).annotate(count=Count('loggedevent__pk')) authusage = baseusage.exclude(loggedevent__authevent__id__lt=1).annotate(count=Count('loggedevent__pk')) return render_to_response('usage.html', { 'ldapusage' : ldapusage, 'authusage' : authusage, }, context_instance=RequestContext(request)) Both ldapusage and authusage are both a list of users, each user annotated with a .count attribute which is supposed to represent how many particular events that user generated. However in both lists, the .count attributes are the same value. Infact the annotated 'count' is equal to how many events that user generated, regardless of type. So it would seem that my specific authusage = baseusage.exclude(loggedevent__authevent__id__lt=1) isn't excluding by subclass. I have tried id_lt=1, id_isnull=True, and others. Halp.

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  • Help, my CentOS servers keep going down , No route to host after a random uptime [closed]

    - by user249071
    Hello , I have a couple of Centos linux servers, that have a very simple task, they run nginx + fastcgi for php , and some NFS mounts between them, readonly They have some RPC commands to start some downloading processes with wget, nothing fancy , from a main server, but their behavior is very unstable, they simply go down, we tried to monitor ram , processor usage, even network connections, they don't load up so much, max network connections up to... 250 max, 15% processor usage and memory , well, doesn't even fill up, 2.5GB from 8GB max , I have no ideea why can a linux server go down like that, they aren't even public servers, no domain names installed no public serving, for sites. The only thing that I've discovered was that if i didn't restart the network service every couple of hours or so... the servers were becoming very slow, starting apps very slow, but not repoting a high usage of resources...Maybe Centos doesn't free the timeout connections, or something like that...It's based on Red Hat right? I'm not a linux expert , but I'm sure that there are a few guys out there that can easily have an answer to this , or even have some leads to what i can do ... I haven't installed snort, or other things to view if we have some DOS attacks, still the scheduled script that restarts the network each hour should put the system back online, and it doesn't.... Thank you in advance

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  • Why can I query with an int but not a string here? PHP MySQL Datatypes

    - by CT
    I am working on an Asset Database problem. I receive $id from $_GET["id"]; I then query the database and display the results. This works if my id is an integer like "93650" but if it has other characters like "wci1001", it displays this MySQL error: Unknown column 'text' in 'where clause' All fields in tables are of type: VARCHAR(50) What would I need to do to be able to use this query to search by id that includes other characters? Thank you. <?php <?php /* * ASSET DB FUNCTIONS SCRIPT * */ # connect to database function ConnectDB(){ mysql_connect("localhost", "asset_db", "asset_db") or die(mysql_error()); mysql_select_db("asset_db") or die(mysql_error()); } # find asset type returns $type function GetAssetType($id){ $sql = "SELECT asset.type From asset WHERE asset.id = $id"; $result = mysql_query($sql) or die(mysql_error()); $row = mysql_fetch_assoc($result); $type = $row['type']; return $type; } # query server returns $result (sql query array) function QueryServer($id){ $sql = " SELECT asset.id ,asset.company ,asset.location ,asset.purchaseDate ,asset.purchaseOrder ,asset.value ,asset.type ,asset.notes ,server.manufacturer ,server.model ,server.serialNumber ,server.esc ,server.warranty ,server.user ,server.prevUser ,server.cpu ,server.memory ,server.hardDrive FROM asset LEFT JOIN server ON server.id = asset.id WHERE asset.id = $id "; $result = mysql_query($sql); return $result; } # get server data returns $serverArray function GetServerData($result){ while($row = mysql_fetch_assoc($result)) { $id = $row['id']; $company = $row['company']; $location = $row['location']; $purchaseDate = $row['purchaseDate']; $purchaseOrder = $row['purchaseOrder']; $value = $row['value']; $type = $row['type']; $notes = $row['notes']; $manufacturer = $row['manufacturer']; $model = $row['model']; $serialNumber = $row['serialNumber']; $esc = $row['esc']; $warranty = $row['warranty']; $user = $row['user']; $prevUser = $row['prevUser']; $cpu = $row['cpu']; $memory = $row['memory']; $hardDrive = $row['hardDrive']; $serverArray = array($id, $company, $location, $purchaseDate, $purchaseOrder, $value, $type, $notes, $manufacturer, $model, $serialNumber, $esc, $warranty, $user, $prevUser, $cpu, $memory, $hardDrive); } return $serverArray; } # print server table function PrintServerTable($serverArray){ $id = $serverArray[0]; $company = $serverArray[1]; $location = $serverArray[2]; $purchaseDate = $serverArray[3]; $purchaseOrder = $serverArray[4]; $value = $serverArray[5]; $type = $serverArray[6]; $notes = $serverArray[7]; $manufacturer = $serverArray[8]; $model = $serverArray[9]; $serialNumber = $serverArray[10]; $esc = $serverArray[11]; $warranty = $serverArray[12]; $user = $serverArray[13]; $prevUser = $serverArray[14]; $cpu = $serverArray[15]; $memory = $serverArray[16]; $hardDrive = $serverArray[17]; echo "<table width=\"100%\" border=\"0\"><tr><td style=\"vertical-align:top\"><table width=\"100%\" border=\"0\"><tr><td colspan=\"2\"><h2>General Info</h2></td></tr><tr id=\"hightlight\"><td>Asset ID:</td><td>"; echo $id; echo "</td></tr><tr><td>Company:</td><td>"; echo $company; echo "</td></tr><tr id=\"hightlight\"><td>Location:</td><td>"; echo $location; echo "</td></tr><tr><td>Purchase Date:</td><td>"; echo $purchaseDate; echo "</td></tr><tr id=\"hightlight\"><td>Purchase Order #:</td><td>"; echo $purchaseOrder; echo "</td></tr><tr><td>Value:</td><td>"; echo $value; echo "</td></tr><tr id=\"hightlight\"><td>Type:</td><td>"; echo $type; echo "</td></tr><tr><td>Notes:</td><td>"; echo $notes; echo "</td></tr></table></td><td style=\"vertical-align:top\"><table width=\"100%\" border=\"0\"><tr><td colspan=\"2\"><h2>Server Info</h2></td></tr><tr id=\"hightlight\"><td>Manufacturer:</td><td>"; echo $manufacturer; echo "</td></tr><tr><td>Model:</td><td>"; echo $model; echo "</td></tr><tr id=\"hightlight\"><td>Serial Number:</td><td>"; echo $serialNumber; echo "</td></tr><tr><td>ESC:</td><td>"; echo $esc; echo "</td></tr><tr id=\"hightlight\"><td>Warranty:</td><td>"; echo $warranty; echo "</td></tr><tr><td colspan=\"2\">&nbsp;</td></tr><tr><td colspan=\"2\"><h2>User Info</h2></td></tr><tr id=\"hightlight\"><td>User:</td><td>"; echo $user; echo "</td></tr><tr><td>Previous User:</td><td>"; echo $prevUser; echo "</td></tr></table></td><td style=\"vertical-align:top\"><table width=\"100%\" border=\"0\"><tr><td colspan=\"2\"><h2>Specs</h2></td></tr><tr id=\"hightlight\"><td>CPU:</td><td>"; echo $cpu; echo "</td></tr><tr><td>Memory:</td><td>"; echo $memory; echo "</td></tr><tr id=\"hightlight\"><td>Hard Drive:</td><td>"; echo $hardDrive; echo "</td></tr><tr><td colspan=\"2\">&nbsp;</td></tr><tr><td colspan=\"2\">&nbsp;</td></tr><tr><td colspan=\"2\"><h2>Options</h2></td></tr><tr><td colspan=\"2\"><a href=\"#\">Edit Asset</a></td></tr><tr><td colspan=\"2\"><a href=\"#\">Delete Asset</a></td></tr></table></td></tr></table>"; } ?> __ /* * View Asset * */ # include functions script include "functions.php"; $id = $_GET["id"]; if (empty($id)):$id="000"; endif; ConnectDB(); $type = GetAssetType($id); ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="stylesheet" type="text/css" href="style.css" /> <title>Wagman IT Asset</title> </head> <body> <div id="page"> <div id="header"> <img src="images/logo.png" /> </div> </div> <div id="content"> <div id="container"> <div id="main"> <div id="menu"> <ul> <table width="100%" border="0"> <tr> <td width="15%"></td> <td width="30%%"><li><a href="index.php">Search Assets</a></li></td> <td width="30%"><li><a href="addAsset.php">Add Asset</a></li></td> <td width="25%"></td> </tr> </table> </ul> </div> <div id="text"> <ul> <li> <h1>View Asset</h1> </li> </ul> <?php if (empty($type)):echo "<ul><li><h2>Asset ID does not match any database entries.</h2></li></ul>"; else: switch ($type){ case "Server": $result = QueryServer($id); $ServerArray = GetServerData($result); PrintServerTable($ServerArray); break; case "Desktop"; break; case "Laptop"; break; } endif; ?> </div> </div> </div> <div class="clear"></div> <div id="footer" align="center"> <p>&nbsp;</p> </div> </div> <div id="tagline"> Wagman Construction - Bridging Generations since 1902 </div> </body> </html>

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  • Adding Mysql Columns in Rails Rake

    - by Gigg
    I have a rake file that does a series of calculations on a database. Basically it adds usage on equipment regularly. At the end of the day it needs to add that days total to a monthly total table and update that same table. i use the following simple concepts: To get data from the database is pretty simple: @usages = Usage.find(:all) time = Time.new for usage in @usages sql = ActiveRecord::Base.connection To insert it into the database: sql.execute "INSERT (or UPDATE) into usages ## add values and options as per MySQL But how do I: take a column from a database, add all of its values together that have a common value in another column, (i.e. if column x == value y) and then insert it into another column in another table, say dailyusages? I have tried these options: task (:monthly => :environment) do @dailyusages = Dailyusage.find(:all) for dailyusage in @dailyusages sql = ActiveRecord::Base.connection time = Time.new device = monthlyusages.device month = time.month if device == dailyusages.device ##&& month == dailyusages.month total = (dailyusage.total.sum.to_i) @monthlyusages = Monthlyusage.find(:all) for monthlyusage in @monthlyusages sql = ActiveRecord::Base.connection old_total = monthlyusage.total.to_i new_total = (old_total + total) sql.execute "UPDATE monthlyusages ( year, month, total, device ) values('#{time.year}', '#{time.month}', '#{total}', '#{dailyusage.device}' )" end I obviously have uncommented options and tried all sorts of things. Any help would really save me a load of trouble. Thanks in advance. (** BTW - I am new to rails, so go easy on me **)

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  • SQL Compact performance on device

    - by Ben M
    My SQL Compact database is very simple, with just three tables and a single index on one of the tables (the table with 200k rows; the other two have less than a hundred each). The first time the .sdf file is used by my Compact Framework application on the target Windows Mobile device, the system hangs for well over a minute while "something" is done to the database: when deployed, the DB is 17 megabytes, and after this first usage, it balloons to 24 megs. All subsequent usage is pretty fast, so I'm assuming there's some sort of initialization / index building going on during this first usage. I'd rather not subject the user to this delay, so I'm wondering what this initialization process is and whether it can be performed before deployment. For now, I've copied the "initialized" database back to my desktop for use in the setup project, but I'd really like to have a better answer / solution. I've tried "full compact / repair" in the VS Database Properties dialog, but this made no difference. Any ideas? For the record, I should add that the database is only read from by the device application -- no modifications are made by that code.

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  • C Programming. How to deep copy a struct?

    - by user69514
    I have the following two structs where "child struct" has a "rusage struct" as an element. Then I create two structs of type "child" let's call them childA and childB How do I copy just the rusage struct from childA to childB? typedef struct{ int numb; char *name; pid_t pid; long userT; long systemT; struct rusage usage; }child; typedef struct{ struct timeval ru_utime; /* user time used */ struct timeval ru_stime; /* system time used */ long ru_maxrss; /* maximum resident set size */ long ru_ixrss; /* integral shared memory size */ long ru_idrss; /* integral unshared data size */ long ru_isrss; /* integral unshared stack size */ long ru_minflt; /* page reclaims */ long ru_majflt; /* page faults */ long ru_nswap; /* swaps */ long ru_inblock; /* block input operations */ long ru_oublock; /* block output operations */ long ru_msgsnd; /* messages sent */ long ru_msgrcv; /* messages received */ long ru_nsignals; /* signals received */ long ru_nvcsw; /* voluntary context switches */ long ru_nivcsw; /* involuntary context switches */ }rusage; I did the following, but I guess it copies the memory location, because if I changed the value of usage in childA, it also changes in childB. memcpy(&childA,&childB, sizeof(rusage)); I know that gives childB all the values from childA. I have already taken care of the others fields in childB, I just need to be able to copy the rusage struct called usage that resides in the "child" struct.

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  • parse a special xml in python

    - by zhaojing
    I have s special xml file like below: <alarm-dictionary source="DDD" type="ProxyComponent"> <alarm code="402" severity="Alarm" name="DDM_Alarm_402"> <message>Database memory usage low threshold crossed</message> <description>dnKinds = database type = quality_of_service perceived_severity = minor probable_cause = thresholdCrossed additional_text = Database memory usage low threshold crossed </description> </alarm> ... </alarm-dictionary> I know in python, I can get the "alarm code", "severity" in tag alarm by: for alarm_tag in dom.getElementsByTagName('alarm'): if alarm_tag.hasAttribute('code'): alarmcode = str(alarm_tag.getAttribute('code')) And I can get the text in tag message like below: for messages_tag in dom.getElementsByTagName('message'): messages = "" for message_tag in messages_tag.childNodes: if message_tag.nodeType in (message_tag.TEXT_NODE, message_tag.CDATA_SECTION_NODE): messages += message_tag.data But I also want to get the value like dnkind(database), type(quality_of_service), perceived_severity(thresholdCrossed) and probable_cause(Database memory usage low threshold crossed ) in tag description. That is, I also want to parse the content in the tag in xml. Could anyone help me with this? Thanks a lot!

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  • how to create an object using self?

    - by Nick
    I thought I understood the use of self while referring to anything in the current class. After encountering this warning and subsequent run failure, I have googled many variants of "define self" or "usage of self" and gotten nowhere. This problem is how to create an object without the warning, and understand why. #import <Cocoa/Cocoa.h> @interface Foo : NSObject { Foo *obj; } -(void)beta; @end #import "Foo.h" @implementation Foo -(void)beta{ obj = [self new]; // 'Foo' may not respond to '-new' } @end Note, if I substitute Foo for self, there's no problem. I thought the class name and self were equivalent, but obviously the compiler doesn't think so. Perhaps an explanation of what's wrong here will not only solve my problem but also enlighten my understanding of the usage of self. Are there any tutorials about proper usage of self? I couldn't find anything beyond something like "self is the receiver of the message," which I didn't help me at all.

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  • What's the point of indicating AllowMultiple=false on an abstract Attribute class?

    - by tvanfosson
    On a recent question about MVC attributes, someone asked whether using HttpPost and HttpDelete attributes on an action method would result in either request type being allowed or no requests being allowed (since it can't be both a Post and a Delete at the same time). I noticed that ActionMethodSelectorAttribute, from which HttpPostAttribute and HttpDeleteAttribute both derive is decorated with [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)] I had expected it to not allow both HttpPost and HttpDelete on the same method because of this, but the compiler doesn't complain. My limited testing tells me that the attribute usage on the base class is simply ignored. AllowMultiple seemingly only disallows two of the same attribute from being applied to a method/class and doesn't seem to consider whether those attributes derive from the same class which is configured to not allow multiples. Moreover, the attribute usage on the base class doesn't even preclude your from changing the attribute usage on a derived class. That being the case, what's the point of even setting the values on the base attribute class? Is it just advisory or am I missing something fundamental in how they work? FYI - it turns out that using both basically precludes that method from ever being considered. The attributes are evaluated independently and one of them will always indicate that the method is not valid for the request since it can't simultaneously be both a Post and a Delete.

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  • BIOS interrupts, privilege levels and paging

    - by Jack
    Hi, I was learning about Intel 8086-80486 CPUs and their interactions with HW. But I still don´t understand it quite well. Please, help me fill blank spots. First, I know that CPU communicates with HW using BIOS interrupts. But, what really happens in PC, when I call some INT instruction? I know that according the interrupt table some instructions begin to execute, but how by executing some instructions can BIOS recognize what I want to do? Becouse as far as I know, CPU has no extra communication channel with BIOS, it can only adress memory and receive data. So how can I instruct BIOS to do something, when I can only address RAM? Next thing I don't understand is about privilege levels. I know about ring model, and access rights, but how does the CPU know which privilege level has executed an instruction? I think that these privileges apply only when intruction is trying to address memory, but how does an application get its privilege level? I mean I know its level 3, but how is it set? And last thing, I know that paging is address scheme that is used to support aplication-transparent virtual memory, or swapping, but I could not find any information about how paging is tied with protected mode. Like if paging is like next mode independent of protected mode, or its somehow implemented within protected mode. And if it is implemented in protected mode, isn´t it too slow, to first address application space, then offset, and then paging folder, page and offset once again?

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  • BIOS interrupts, priviledge levels and paging

    - by Jack
    Hi, I was learning about Intel 8086-80486 CPUs and their interactions with HW. But I still don´t understand it quite well. Please, help me fill blank spots. First, I know that CPU communicates with HW using BIOS interrupts. But, what really happens in PC, when I call some INT instruction? I know that according the interrupt table some instructions begin to execute, but how by executing some instructions can BIOS recognize what I want to do? Becouse as far as I know, CPU has no extra communication channel with BIOS, it can only adress memory and receive data. So how can I instruct BIOS to do something, when I can only adress RAM? Next thing I dont understand is about priviledge levels. I know about ring model, and acess rights, but how CPU knows which priviledge level has executed instruction? I think that these priviledges apply only when intruction is trying to adress memory, but how applications gets its priviledge level? I mean I know its level 3, but how its set? And last thing, I know that paging is adress scheme that is used to support aplication-transparent virtual memory, or swaping, but I could not find any informations about how is paging tied with protected mode. Like if paging is like next mode independent of protectet mode, or its somehow implemented within protected mode. And if it is implemented in protected mode, isn´t it too slow, to first adress application space, than offset, and than paging folder, page and offset once again? Thank you for every response.

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  • The boot selection failed because a required device is inaccessible 0xc000000e

    - by bbodenmiller
    A family member of mine recently went on vacation and turned off their computer, something they normally do not do, upon returning home it would not turn on and now returns the error message below. Generally friends and family come to me for help with computers and I have no problem, however this time I am a bit stumped. Any suggestions would be greatly appreciated. As you can see the error message is: Status: 0xc000000e Info: The best selection failed because a required device is inaccessible. Before going to this error message it briefly flashes the Windows loading screen. I have been able to confirm through the Windows RE Command Line and the dir command that the C: drive is accessible and likely is just suffering a bootup issue. I have tried: Launching the repair process discussed in the error message three times however each time it requires a restart and then returns to the same error message. Changing the boot order to be hard drive first Getting into safe mode; F8 just results in the same error message before I can get to the menu to select safe mode I have checked to make sure the BCD (bcdedit, Boot Configuration Data) is still intact as per https://www.symantec.com/business/support/index?page=content&id=TECH160475 I plan to try (but would like additional comments on): sfc /scannow; requires a restart and thus will likely result in the error message again A memory scan Bootrec as per http://support.microsoft.com/kb/927392#method1 Swapping IDE cables/ports Resetting the BIOS I noticed others with similar issues around the web are dual-booting however this machine is not setup in a dual-boot environment. Additionally at one point this error message supposedly showed up before I started working on the computer: The instruction at 0xfbe2584d referenced memory at 0x00000008. The memory could not be read. As previously stated any additional suggestions or words of advice would be greatly apprecaited.

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  • PHP-FPM and APC for shared hosting?

    - by Tiffany Walker
    We are looking into finding a way to get APC to only create one cache per account / site. This can be done with Fastcgi (last update 2006…) but with Fastcgid APC will have to create multiple caches for multiple processes run by the same account. To get around this problem, we have been looking into PHP-FPM PHP process manager allows multiple PHP processes to share a single APC cache. But from what I have read (I hope I'm wrong) , even if you create a pool per process, all sites accross all pools will share the same APC cache. This brings us back to the same problem as with shared Memcached: it's not secure ! On php-fpm's site I read that you can chroot php-fpm pools and define a specific UID and GID per pool… if this is the case then shouldn't APC have to use this user and not have access to other pools cache ? An article here (in 2011) suggests that you would need to run one process per pool creating multiple launchers on different ports and different config files with one pool per config file : http://groups.drupal.org/node/198168 Is this still neceessary ? If so what would be the impact of running say 800 processes of php-fpm ? Would it be mainly memory ? If so how can I work out what the memory impact would be ? I guess that it would be better to run 800 times php-fpm then to have accounts creating multiple APC caches for a single site ? If on average an account creates a 50MB cache and creates 3 caches per account that makes 150Mb per account which makes 120GB… However if each account uses on average only 50Mb that would make 40GB We will have at least 128GB of ram on our next server so 40GB is acceptable if running 800 x PHP-FPM does not create an overhead of more than 20GB ! What do you think is PHP-FPM the best way to go to provide secure APC cache on shared hosting with a server that has a decent amount of memory ? Or should I be looking at another system ? Thanks !

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  • How to set shmall, shmmax, shmni, etc ... in general and for postgresql

    - by jpic
    I've used the documentation from PostgreSQL to set it for example this config: >>> cat /proc/meminfo MemTotal: 16345480 kB MemFree: 1770128 kB Buffers: 382184 kB Cached: 10432632 kB SwapCached: 0 kB Active: 9228324 kB Inactive: 4621264 kB Active(anon): 7019996 kB Inactive(anon): 548528 kB Active(file): 2208328 kB Inactive(file): 4072736 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 3432 kB Writeback: 0 kB AnonPages: 3034588 kB Mapped: 4243720 kB Shmem: 4533752 kB Slab: 481728 kB SReclaimable: 440712 kB SUnreclaim: 41016 kB KernelStack: 1776 kB PageTables: 39208 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 8172740 kB Committed_AS: 14935216 kB VmallocTotal: 34359738367 kB VmallocUsed: 399340 kB VmallocChunk: 34359334908 kB HardwareCorrupted: 0 kB AnonHugePages: 456704 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 12288 kB DirectMap2M: 16680960 kB >>> ipcs -l ------ Shared Memory Limits -------- max number of segments = 4096 max seg size (kbytes) = 4316816 max total shared memory (kbytes) = 4316816 min seg size (bytes) = 1 ------ Semaphore Limits -------- max number of arrays = 128 max semaphores per array = 250 max semaphores system wide = 32000 max ops per semop call = 32 semaphore max value = 32767 ------ Messages Limits -------- max queues system wide = 31918 max size of message (bytes) = 8192 default max size of queue (bytes) = 16384 sysctl.conf extract: kernel.shmall = 1079204 kernel.shmmax = 4420419584 postgresql.conf non defaults: max_connections = 60 # (change requires restart) shared_buffers = 4GB # min 128kB work_mem = 4MB # min 64kB wal_sync_method = open_sync # the default is the first option checkpoint_segments = 16 # in logfile segments, min 1, 16MB each checkpoint_completion_target = 0.9 # checkpoint target duration, 0.0 - 1.0 effective_cache_size = 6GB Is this appropriate ? If not (or not necessarily), in which case would it be appropriate ? We did note nice performance improvements with this config, how would you improve it ? How should kernel memory management parameters be set ? Can anybody explain how to really set them from the ground up ?

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  • Laptop choice for development: MacBook Pro 17 vs Dell Studio XPS 16 vs HP Envy 15

    - by Shalan
    Hey! First things first - let me state that I am not intending to play games on this - I have narrowed down to these 3 purely based on specs and its individual brand reliability in the market. I intend to primarily use: Visual Studio 2008 Pro a lot (develop and deploy on Windows platforms) SQL Server 2005 Oracle 10g Adobe Photoshop CS4 Microsoft Expression Studio Google Sketchup I currently use a desktop PC (Core2Duo 2.66Ghz with 3GB DDRII memory) running Vista Business 32-bit - and I have to admit that, especially for Visual Studio, its quite sluggish to a point where it affects productivity. Furthermore, I intend to only use the notebook on a table - with a cooled surface, like granite :) - so I would appreciate people's input with regard to heat issues. Im aware that the Dell's primary exhaust gets blocked by the lid when open, but some reviews don't seem to place extraordinary emphasis on heat issues resulting from this. My options for the Dell/Alienware: Core i7 720QM 4GB DDRIII memory ATI mobility 3670 (512) 128GB Solid State Drive 16-inch Full HD RGB-LED LCD display (1080p) 3-year next-business-day support My configuration for the Apple MBP: Core2Duo 2.8Ghz (Im assuming the T9600) 4GB DDRIII memory 128GB Solid State Drive standard 1 year support The one advantage I think of with the MBP is that I can have the addition of OSX (though Im unsure what I would use it for, but purely to play around with a much-boasted-about OS) What are your thoughts on this, especially regarding build-quality, heat, performance and battery-life? Much thanks! ~shalan

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  • problem booting crusty old windows XP

    - by Carson Myers
    I have an acer aspire laptop running Windows XP home. I believe I have some virus on it, I'm not sure--I mostly just run linux in a VM on it so I wasn't too worried. I'm not sure if that virus caused this problem. The laptop wasn't recognizing my USB hard drive for some reason so I decided to restart it. When it started up, it got past the memory test, past the boot screen, (but it paused right here on a blank screen for awhile) and flashed the desktop once (like it does just before the login screen) and then crashed. I got a quick BSOD and then it restarted. Then it tried to boot again, etc etc infinite loop of failure. Well, before trying safe mode, I disabled automatic restart on system crash so I could read the blue screen. There wasn't anything important on it, it said *** STOP: 0x00000000 (0xC0000000 0x,.... ) beginning physical memory dump physical memory dump complete That's not verbatim (obviously) but it didn't help me. so I booted in safe mode, and it stopped on the driver gagp30kx.sys and then restarted (and infinite loop of failure again). I burned a recovery CD and tried that. It loaded it, and I went into repair mode. I ran chkdsk and then disabled the AGP driver. Same thing on booting in safe mode except it stopped at mup.sys instead. I enabled the AGP driver again, and ran chkdsk again from the CD. It said it found problems but didn't say it fixed them. So I ran it a second time, and it said "performing additional checking or recovery" lots of times (I can't tell how many, they went above the screen top). I tried booting again and no luck. Every time I run chkdsk after trying to boot again it says it found and fixed more errors. I think it might be whatever driver is after the AGP driver, but I don't know what it is or how to find out. Can anyone help me fix this?

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  • Why does my computer crash randomly?

    - by Donavon Decker
    The other day I went out to my van to get my Tower and when I opened the trunk it fell out. I brought it into the house and opened it, and everything looked ok. When I started it up, about 1-3 minutes afterwards it would crash. It did this over and over until I reseated the cooler. Everything seemed normal again, until after about 10 minutes of gameplay (any game), it would crash. I reseated my GPU + reinstalled the drivers, however I still get the same error. A while back, I'd check my 'Windows Rating' periodically, and all of them were in the '6.0-6.9' range except for my hard disk usage (always been like that [not relative]). Today I went in and looked, and my Processor and Memory was rated 5.4. I reseated my cpu and my memory, refreshed the windows rating, and then my processor and memory went from 5.4, to 5.1. A few minutes ago I reseated them once again, and now it's back to 5.4. Note: Not sure if this is relevant to the issue, but I updated my bios earlier today I honestly have no idea what the issue is, but I'm getting aggravated at the problem. Here are some images which contain images of my specifications: i1271.photobucket.com/albums/jj623/donxdeck/1_zps09f0607c.jpg i1271.photobucket.com/albums/jj623/donxdeck/4_zps381cd00a.jpg i1271.photobucket.com/albums/jj623/donxdeck/3_zps54bba720.jpg i1271.photobucket.com/albums/jj623/donxdeck/2_zps945d3d72.jpg Thanks for the help

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  • 613 threads limit on debian

    - by Joel
    When running this program thread-limit.c on my dedicated debian server, the output says that my system can't create more than around 600 threads. I need to create more threads, and fix my system misconfiguration. Here are a few informations about my dedicated server: de801:/# uname -a Linux de801.ispfr.net 2.6.18-028stab085.5 #1 SMP Thu Apr 14 15:06:33 MSD 2011 x86_64 GNU/Linux de801:/# java -version java version "1.6.0_26" Java(TM) SE Runtime Environment (build 1.6.0_26-b03) Java HotSpot(TM) 64-Bit Server VM (build 20.1-b02, mixed mode) de801:/# ldd $(which java) linux-vdso.so.1 => (0x00007fffbc3fd000) libpthread.so.0 => /lib/libpthread.so.0 (0x00002af013225000) libjli.so => /usr/lib/jvm/java-6-sun-1.6.0.26/jre/bin/../lib/amd64/jli/libjli.so (0x00002af013441000) libdl.so.2 => /lib/libdl.so.2 (0x00002af01354b000) libc.so.6 => /lib/libc.so.6 (0x00002af013750000) /lib64/ld-linux-x86-64.so.2 (0x00002af013008000) de801:/# cat /proc/sys/kernel/threads-max 1589248 de801:/# ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 794624 max locked memory (kbytes, -l) 32 max memory size (kbytes, -m) unlimited open files (-n) 10240 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 128 cpu time (seconds, -t) unlimited max user processes (-u) unlimited virtual memory (kbytes, -v) unlimited file locks (-x) unlimited Here is the output of the C program de801:/test# ./thread-limit Creating threads ... Address of c = 1061520 KB Address of c = 1081300 KB Address of c = 1080904 KB Address of c = 1081168 KB Address of c = 1080508 KB Address of c = 1080640 KB Address of c = 1081432 KB Address of c = 1081036 KB Address of c = 1080772 KB 100 threads so far ... 200 threads so far ... 300 threads so far ... 400 threads so far ... 500 threads so far ... 600 threads so far ... Failed with return code 12 creating thread 637. Any ideas how to fix this please ?

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  • Why won't 2GB of ram across 3 of 4 slots work on my motherboard (max 2GB)?

    - by Andrew
    My desktop is an old home-built machine circa 200[5-6] running Ubuntu 11.10 (but this is not relevant because I'm reading available ram from BIOS loading screen), with an ASUS P5GPL motherboard, not X or X-SE - it has four slots. I'm mainly a laptop person, but keep this around for running a server from if needed, backing up to, seeding Ubuntu to people from, etc… It has four (DDR) ram slots, two black and two blue, in the order black-blue-black-blue (I will call them D, C, B, and A, respectively) with some space in the middle. The blue ones are the closest to the processor. I used to have two 512MB chips in the two blue slots. I just got a 1GB chip and plugged it into one of the black slots; my system didn't recognize it. I messed around and discovered that it will not recognize chips in many positions, and I couldn't get it to recognize all three of these chips at the same time. In particular, if I put the 512MB chips in A and B it would only use 1, but AC, AD, BD, and CD worked. I didn't try BC, I believe. Only some of these continue to work when I switch the 1GB chip into one of these positions. Can I have some advice as to how to position these chips to get all 2GB used? How about if I get another 1GB chip - where should I put the two? And what about the RAM maximum Crucial says? Can I go above 2GB, if I get another 1GB chip? Right now, I have a 512MB chip in A and the 1GB chip in C. EDIT: I read some other posts and tried dmidecode in Ubuntu to clarify the max memory question, that wasn't a major part anyways. It says my max memory module size is 1024M (OK) and my max memory size is 4096M (doesn't agree with Crucial OR the Asus web site, maybe it will only work while in Linux and BIOS won't OK it?).

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  • PostgreSQL lots of large Arrays and Writes

    - by strife911
    Hi, I am running a python program that spawns 8 threads and as each thread launch its own postmaster process via psycopg2. This is to maximize the use of my CPU-cores (8). Each thread call a series of SQL Functions. Most of these functions go through many thousands of rows each associated to a large FLOAT8[] Array (250-300) values by using unnest() and multiplying each FLOAT8 by an another FLOAT8 associated to each row. This Array approach minimized the size of the Indexes and the Tables. The Function ends with an Insert into another Table of a row of the same form (pk INT4, array FLOAT8[]). Some SQL Functions called by python will Update a row of these kind of Tables (with large Arrays). Now I currently have configured PostgreSQL to use most of the memory for cache (effective_cache_size of 57 GB I think) and only a small amount of it for shared memory (1GB I think). First, I was wondering what the difference between Cache and Shared memory was in regards to PostgreSQL (and my application). What I have noticed is that only about 20-40% of my total CPU processing power is used during the most Read intensive parts of the application (Select unnest(array) etc). So secondly, I was wondering what I could do to improve this so that 100% of the CPU is used. Based on my observations, it does not seem to have anything to do with python or its GIL. Thanks

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  • Fatal Execution Engine Error on the Windows2008 r2, IIS7.5

    - by user66524
    Hi Guys We are running some asp.net(3.5) applications on the Windows2008 r2, IIS7.5. Recently we got some event logs so difficult, we have not idea hope some guys can help. 1.EventID: 1334 (9-1-2011 8:41:57) Error message An error occurred during a process host idle check. Exception: System.AccessViolationException Message: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. StackTrace: at System.Collections.Hashtable.GetEnumerator() at System.Web.Hosting.ApplicationManager.IsIdle() at System.Web.Hosting.ProcessHost.IsIdle() 2.EventID: 1023 (9-1-2011 19:44:02) Error message .NET Runtime version 2.0.50727.4952 - Fatal Execution Engine Error (742B851A) (80131506) 3.EventID: 1000 (9-1-2011 19:44:03) Error message Faulting application name: w3wp.exe, version: 7.5.7600.16385, time stamp: 0x4a5bcd2b Faulting module name: mscorwks.dll, version: 2.0.50727.4952, time stamp: 0x4bebd49a Exception code: 0xc0000005 Fault offset: 0x0000c262 Faulting process id: 0x%9 Faulting application start time: 0x%10 Faulting application path: %11 Faulting module path: %12 Report Id: %13 4.EventID: 5011 (9-1-2011 19:44:03) Error message A process serving application pool 'AppPoolName' suffered a fatal communication error with the Windows Process Activation Service. The process id was '2552'. The data field contains the error number. 5.some info: we got the memory.hdmp(234MB) and minidump.mdmp(19.2) from control panel action center but I donot know how to use that :(

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  • Fatal Execution Engine Error on the Windows2008 r2, IIS7.5

    - by user66524
    Hi Guys We are running some asp.net(3.5) applications on the Windows2008 r2, IIS7.5. Recently we got some event logs so difficult, we have not idea hope some guys can help. 1.EventID: 1334 (9-1-2011 8:41:57) Error message An error occurred during a process host idle check. Exception: System.AccessViolationException Message: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. StackTrace: at System.Collections.Hashtable.GetEnumerator() at System.Web.Hosting.ApplicationManager.IsIdle() at System.Web.Hosting.ProcessHost.IsIdle() 2.EventID: 1023 (9-1-2011 19:44:02) Error message .NET Runtime version 2.0.50727.4952 - Fatal Execution Engine Error (742B851A) (80131506) 3.EventID: 1000 (9-1-2011 19:44:03) Error message Faulting application name: w3wp.exe, version: 7.5.7600.16385, time stamp: 0x4a5bcd2b Faulting module name: mscorwks.dll, version: 2.0.50727.4952, time stamp: 0x4bebd49a Exception code: 0xc0000005 Fault offset: 0x0000c262 Faulting process id: 0x%9 Faulting application start time: 0x%10 Faulting application path: %11 Faulting module path: %12 Report Id: %13 4.EventID: 5011 (9-1-2011 19:44:03) Error message A process serving application pool 'AppPoolName' suffered a fatal communication error with the Windows Process Activation Service. The process id was '2552'. The data field contains the error number. 5.some info: we got the memory.hdmp(234MB) and minidump.mdmp(19.2) from control panel action center but I donot know how to use that :(

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