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• How to recover after embarrassing yourself and your company?

  - by gaearon

  I work in an outsourcing company in Russia, and one of our clients is a financial company located in USA. For the last six months I have been working on several projects for this particular company, and as I was being assigned a larger project, I was invited to work onsite in USA in order to understand and learn the new system. Things didn't work out as well as I hoped because the environment was messy after original developers, and I had to spent quite some time to understand the quirks. However we managed to do the release several days ago, and it looks like everything's going pretty smooth. From technical perspective, my client seems to be happy with me. My solutions seem to work, and I always try to add some spark of creativity to what I do. However I'm very disorganized in a certain sense, as I believe many of you fellas are. Let me note that my current job is my first job ever, and I was lucky enough to get a job with flexible schedule, meaning I can come in and out of the office whenever I want as long as I have 40 hours a week filled. Sometimes I want to hang out with friends in the evening, and days after that I like to have a good sleep in the morning—this is why flexible schedule (or lack of one) is ideal fit for me. [I just realized this paragraph looks too serious, I should've decorated it with some UNICORNS!] Of course, after coming to the USA, things changed. This is not some software company with special treatment for the nerdy ones. Here you have to get up at 7:30 AM to get to the office by 9 AM and then sit through till 5 PM. Personally, I hate waking up in the morning, not to say my productivity begins to climb no sooner than at 5 o'clock, i.e. I'm very slow until I have to go, which is ironic. Sometimes I even stay for more than 8 hours just to finish my current stuff without interruptions. Anyway, I could deal with that. After all, they are paying for my trip, who am I to complain? They need me to be in their working hours to be able to discuss stuff. It makes perfect sense that fixed schedule doesn't make any sense for me. But it does makes sense that it does make sense for my client. And I am here for client, therefore sense is transferred. Awww, you got it. I was asked several times to come exactly at 9 AM but out of laziness and arrogance I didn't take these requests seriously enough. This paid off in the end—on my last day I woke up 10 minutes before final status meeting with business owner, having overslept previous day as well. Of course this made several people mad, including my client, as I ignored his direct request to come in time for two days in the row, including my final day. Of course, I didn't do it deliberately but certainly I could've ensured that I have at least two alarms to wake me up, et cetera...I didn't do that. He also emailed my boss, calling my behavior ridiculous and embarrassing for my company and saying “he's not happy with my professionalism at all”. My boss told me that “the system must work both in and out” and suggested me to stay till late night this day working in a berserker mode, fixing as many issues as possible, and sending a status email to my client. So I did, but I didn't receive the response yet. These are my questions to the great programmers community: Did you have situations where your ignorance and personal non-technical faults created problems for your company? Were you able to make up for your fault and stay in a good relationship with your client or boss? How? How would you act if you were in my situation?

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• SQL Server IO handling mechanism can be severely affected by high CPU usage

  - by sqlworkshops

  Are you using SSD or SAN / NAS based storage solution and sporadically observe SQL Server experiencing high IO wait times or from time to time your DAS / HDD becomes very slow according to SQL Server statistics? Read on… I need your help to up vote my connect item – https://connect.microsoft.com/SQLServer/feedback/details/744650/sql-server-io-handling-mechanism-can-be-severely-affected-by-high-cpu-usage. Instead of taking few seconds, queries could take minutes/hours to complete when CPU is busy.In SQL Server when a query / request needs to read data that is not in data cache or when the request has to write to disk, like transaction log records, the request / task will queue up the IO operation and wait for it to complete (task in suspended state, this wait time is the resource wait time). When the IO operation is complete, the task will be queued to run on the CPU. If the CPU is busy executing other tasks, this task will wait (task in runnable state) until other tasks in the queue either complete or get suspended due to waits or exhaust their quantum of 4ms (this is the signal wait time, which along with resource wait time will increase the overall wait time). When the CPU becomes free, the task will finally be run on the CPU (task in running state).The signal wait time can be up to 4ms per runnable task, this is by design. So if a CPU has 5 runnable tasks in the queue, then this query after the resource becomes available might wait up to a maximum of 5 X 4ms = 20ms in the runnable state (normally less as other tasks might not use the full quantum).In case the CPU usage is high, let’s say many CPU intensive queries are running on the instance, there is a possibility that the IO operations that are completed at the Hardware and Operating System level are not yet processed by SQL Server, keeping the task in the resource wait state for longer than necessary. In case of an SSD, the IO operation might even complete in less than a millisecond, but it might take SQL Server 100s of milliseconds, for instance, to process the completed IO operation. For example, let’s say you have a user inserting 500 rows in individual transactions. When the transaction log is on an SSD or battery backed up controller that has write cache enabled, all of these inserts will complete in 100 to 200ms. With a CPU intensive parallel query executing across all CPU cores, the same inserts might take minutes to complete. WRITELOG wait time will be very high in this case (both under sys.dm_io_virtual_file_stats and sys.dm_os_wait_stats). In addition you will notice a large number of WAITELOG waits since log records are written by LOG WRITER and hence very high signal_wait_time_ms leading to more query delays. However, Performance Monitor Counter, PhysicalDisk, Avg. Disk sec/Write will report very low latency times.Such delayed IO handling also occurs to read operations with artificially very high PAGEIOLATCH_SH wait time (with number of PAGEIOLATCH_SH waits remaining the same). This problem will manifest more and more as customers start using SSD based storage for SQL Server, since they drive the CPU usage to the limits with faster IOs. We have a few workarounds for specific scenarios, but we think Microsoft should resolve this issue at the product level. We have a connect item open – https://connect.microsoft.com/SQLServer/feedback/details/744650/sql-server-io-handling-mechanism-can-be-severely-affected-by-high-cpu-usage - (with example scripts) to reproduce this behavior, please up vote the item so the issue will be addressed by the SQL Server product team soon.Thanks for your help and best regards,Ramesh MeyyappanHome: www.sqlworkshops.comLinkedIn: http://at.linkedin.com/in/rmeyyappan

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• Walkthrough: Scheduling jobs using Quartz.net &ndash; Part 1: What is Quartz.Net?

  - by Tarun Arora

  Quartz.NET is a full-featured, open source enterprise job scheduling system written in .NET platform that can be used from smallest apps to large scale enterprise systems. What is the problem that we trying to address? I want to schedule the execution of a task but only when something happens. Let’s call that something a trigger, so... if the trigger is met => execute the task. Sounds simple, why not use windows task scheduler for this? Well, windows task scheduler is great for tasks where the trigger can be easily defined. With windows task scheduler will you be able to schedule a task to run on every working day according to the UK calendar (exclude all weekends & bank holidays) without either writing the logic for day check in the task or a wrapper script calling into the task. The task should just contain the execution logic and should not have anything to do with the schedule for execution; Quartz.net allows you to achieve this and lots more. A quartz.net trigger gives you the flexibility for task invocation based on the following triggers, 1. at a certain time of day (to the millisecond) 2. on certain days of the week 3. on certain days of the month 4. on certain days of the year 5. not on certain days listed within a registered Calendar (such as business holidays) 6. repeated a specific number of times 7. repeated until a specific time/date 8. repeated indefinitely 9. repeated with a delay interval Did 8 – repeat indefinitely just ring a bell? I’ll be covering that in the future post. Using Quartz.net as a windows service You can have Quartz.net run as a standalone instance within its own .NET virtual machine instance via .NET Remoting. Let’s take a look at typical application architecture. In the figure below, I have the application tier set up on Machine 1, database set up on Machine 2 and Quartz.net set up on Machine 3 which is normally the architecture for most (if not all) enterprise applications. Figure 1 -  Typical Application architecture while using Quartz.net as a windows service What other options do I have if I don’t want to use Quartz.net? Quartz.net is just one of the many job scheduling services. Have a look at this comprehensive list of free and paid enterprise job scheduling software along with their feature comparison. http://en.wikipedia.org/wiki/List_of_job_scheduler_software This was first in the series of posts on enterprise scheduling using Quartz.net, in the next post I’ll be covering how to Install Quartz.net as a windows service. Thank you for taking the time out and reading this blog post. If you enjoyed the post, remember to subscribe to http://feeds.feedburner.com/TarunArora. Stay tuned!

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• PASS Summit 2013 Review

  - by Ajarn Mark Caldwell

  As a long-standing member of PASS who lives in the greater Seattle area and has attended about nine of these Summits, let me start out by saying how GREAT it was to go to Charlotte, North Carolina this year.  Many of the new folks that I met at the Summit this year, upon hearing that I was from Seattle, commented that I must have been disappointed to have to travel to the Summit this year after 5 years in a row in Seattle.  Well, nothing could be further from the truth.  I cheered loudly when I first heard that the 2013 Summit would be outside Seattle.  I have many fond memories of trips to Orlando, Florida and Grapevine, Texas for past Summits (missed out on Denver, unfortunately).  And there is a funny dynamic that takes place when the conference is local.  If you do as I have done the last several years and saved my company money by not getting a hotel, but rather just commuting from home, then both family and coworkers tend to act like you’re just on a normal schedule.  For example, I have a young family, and my wife and kids really wanted to still see me come home “after work”, but there are a whole lot of after-hours activities, social events, and great food to be enjoyed at the Summit each year.  Even more so if you really capitalize on the opportunities to meet face-to-face with people you either met at previous summits or have spoken to or heard of, from Twitter, blogs, and forums.  Then there is also the lovely commuting in Seattle traffic from neighboring cities rather than the convenience of just walking across the street from your hotel.  So I’m just saying, there are really nice aspects of having the conference 2500 miles away. Beyond that, the training was fantastic as usual.  The SQL Server community has many outstanding presenters and experts with deep knowledge of the tools who are extremely willing to share all of that with anyone who wants to listen.  The opening video with PASS President Bill Graziano in a NASCAR race turned dream sequence was very well done, and the keynotes, as usual, were great.  This year I was particularly impressed with how well attended were the Professional Development sessions.  Not too many years ago, those were very sparsely attended, but this year, the two that I attended were standing-room only, and these were not tiny rooms.  I would say this is a testament to both the maturity of the attendees realizing how important these topics are to career success, as well as to the ever-increasing skills of the presenters and the program committee for selecting speakers and topics that resonated with people.  If, as is usually the case, you were not able to get to every session that you wanted to because there were just too darn many good ones, I encourage you to get the recordings. Overall, it was a great time as these events always are.  It was wonderful to see old friends and make new ones, and the people of Charlotte did an awesome job hosting the event and letting their hospitality shine (extra kudos to SQLSentry for all they did with the shuttle, maps, and other event sponsorships).  We’re back in Seattle next year (it is a release year, after all) but I would say that with the success of this year’s event, I strongly encourage the Board and PASS HQ to firmly reestablish the location rotation schedule.  I’ll even go so far as to suggest standardizing on an alternating Seattle – Charlotte schedule, or something like that. If you missed the Summit this year, start saving now, and register early, so you can join us!

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• RemoveHandler Issues with Custom Events

  - by Jeff Certain

  This is a case of things being more complicated that I thought they should be. Since it took a while to figure this one out, I thought it was worth explaining and putting all of the pieces to the answer in one spot. Let me set the stage. Architecturally, I have the notion of generic producers and consumers. These put items onto, and remove items from, a queue. This provides a generic, thread-safe mechanism to load balance the creation and processing of work items in our application. Part of the IProducer(Of T) interface is: 1: Public Interface IProducer(Of T) 2: Event ItemProduced(ByVal sender As IProducer(Of T), ByVal item As T) 3: Event ProductionComplete(ByVal sender As IProducer(Of T)) 4: End Interface Nothing sinister there, is there? In order to simplify our developers’ lives, I wrapped the queue with some functionality to manage the produces and consumers. Since the developer can specify the number of producers and consumers that are spun up, the queue code manages adding event handlers as the producers and consumers are instantiated. Now, we’ve been having some memory leaks and, in order to eliminate the possibility that this was caused by weak references to event handles, I wanted to remove them. This is where it got dicey. My first attempt looked like this: 1: For Each producer As P In Producers 2: RemoveHandler producer.ItemProduced, AddressOf ItemProducedHandler 3: RemoveHandler producer.ProductionComplete, AddressOf ProductionCompleteHandler 4: producer.Dispose() 5: Next What you can’t see in my posted code are the warnings this caused. The 'AddressOf' expression has no effect in this context because the method argument to 'AddressOf' requires a relaxed conversion to the delegate type of the event. Assign the 'AddressOf' expression to a variable, and use the variable to add or remove the method as the handler.  Now, what on earth does that mean? Well, a quick Bing search uncovered a whole bunch of talk about delegates. The first solution I found just changed all parameters in the event handler to Object. Sorry, but no. I used generics precisely because I wanted type safety, not because I wanted to use Object. More searching. Eventually, I found this forum post, where Jeff Shan revealed a missing piece of the puzzle. The other revelation came from Lian_ZA in this post. However, these two only hinted at the solution. Trying some of what they suggested led to finally getting an invalid cast exception that revealed the existence of ItemProducedEventHandler. Hold on a minute! I didn’t create that delegate. There’s nothing even close to that name in my code… except the ItemProduced event in the interface. Could it be? Naaaaah. Hmmm…. Well, as it turns out, there is a delegate created by the compiler for each event. By explicitly creating a delegate that refers to the method in question, implicitly cast to the generated delegate type, I was able to remove the handlers: 1: For Each producer As P In Producers 2: Dim _itemProducedHandler As IProducer(Of T).ItemProducedEventHandler = AddressOf ItemProducedHandler 3: RemoveHandler producer.ItemProduced, _itemProducedHandler 4:  5: Dim _productionCompleteHandler As IProducer(Of T).ProductionCompleteEventHandler = AddressOf ProductionCompleteHandler 6: RemoveHandler producer.ProductionComplete, _productionCompleteHandler 7: producer.Dispose() 8: Next That’s “all” it took to finally be able to remove the event handlers and maintain type-safe code. Hopefully, this will save you the same challenges I had in trying to figure out how to fix this issue!

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• How do you automatically close 3rd party applications when LiberKey is shut down?

  - by NoCatharsis

  Within LiberKey, I have added my own portable applications that are not included within the LiberKey library. When you go into the Properties menu for the app in the LiberKey UI, the Advanced tab has an option for Autoexecute. This dropdown menu seems to have no visible effect, at least on my current installation. I found that I could right click within the primary GUI and select "Add software group", add all 3rd party applications, then go to the Advanced tab within THAT Properties screen and select Autoexecute - "Always on startup". This solved the problem for starting the apps when LiberKey starts. However, now I'm having the same issue when closing out LiberKey. I have created a new 3rd party app that calls the same .exe, but sends the Parameter "/close". I then went to the Advanced tab and selected Autoexecute - "Always on shutdown". Seems pretty logical right? But the apps will not close on LiberKey shutdown. I cannot handle the app close-outs in the same way with a software group, as I did with the startup issue because the Autoexecute drop-down does not have an "Always on shutdown" option. Unfortunately, many of the Q&A forums on liberkey.com are in French and I took Spanish in high school. Otherwise I've not been able to find a workable answer. Any suggestions?

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• Missing boot files in Windows 8

  - by Alex F. Sherman

  I had a partition with Windows 8 Release Preview, Windows' System Reserved partition and the empty space of the beginning of disk. I moved two partitions to the beginning of disk using Ubuntu Live CD and GParted. After that, the Windows Loader didn't boot and throw an error about missing files. I fixed it using the commands: bootsect /nt60 sys /force /mbr bootrec /rebuildbcd bootrec /fixboot bootrec /fixmbr When I used "Automatic repair" option from "Advanced boot" menu, it throw an error like: Windows can't fix your boot problems. For more information see file C:\Windows\System32\LogFiles\Srt\SrtTrail.txt In this file I found a description of the system repair actions and at the end of file: Boot status indicates that the OS booted successfully. Now, when I use the Advanced boot menu from Windows 8 (PC settings - General - Advanced startup) I receive an error: Restart your PC to try again. It looks like something didn't load correctly. Restarting might fix the problem. If this happens more than once, you might also be able to find help by searching online for the specific error code. Erorr code: 0x8007090. 0x80070490 is the error code ERROR_NOT_FOUND. What are the missing boot files and how can I restore them? List of files in System Reserved Partition: B:\bootmgr B:\BOOTNXT B:\Boot\BCD B:\Boot\BCD.LOG B:\Boot\BCD.LOG1 B:\Boot\BCD.LOG2 B:\Boot\BOOTSTAT.DAT B:\Boot\Fonts B:\Boot\memtest.exe B:\Boot\qps-ploc B:\Boot\Resources B:\Boot\Resources\bootres.dll and many *.mui and *.ttf files.

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• We have multiple app servers running against a single database. How do I ensure that each row in a q

  - by Dave

  We have about 7 app servers running .NET windows services that ping a single sql server 2005 queue table and fetch a fixed amount of records to process at fixed intervals. The amount of records to process and the amount of time between fetches are both configurable and are initially set to 100 and 30 seconds initially. Currently, my queue table has an int status column which can be either "Ready, Processing, Complete, Error". The proc that fetches the records has a sql transaction with the following code inside the transaction: 1) Fetch x number of records into temp table where the status is "Ready". The select uses a holdlock hint 2) Update the status on those records in the Queue table to "Processing" The .NET services do some processing that may take seconds or even minutes per record. Another proc is called per record that simply updates the status to "Complete". The update proc has no transaction as I'm leaning on the implicit transaction as part of the update clause here. I don't know the traffic exceptions for this but figure it will be under 10k records per day. Is this the best way to handle this scenario? If so, are there any details that I've left out, such as a hint here or there? Thanks! Dave

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• Running and managing NSTimer in different NSThread/NSRunLoop

  - by mips

  I'm writing a Cocoa application, with a GUI designed in Interface Builder. I need to schedule background activity (at regular intervals) without blocking the UI, so I run it in a separate thread, like this: - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { [self performSelectorInBackground:@selector(schedule) withObject:nil]; } - (void) schedule { NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init]; NSRunLoop* runLoop = [NSRunLoop currentRunLoop]; timer = [[NSTimer scheduledTimerWithTimeInterval:FEED_UPDATE_INTERVAL target:activityObj selector:@selector(run:) userInfo:nil repeats:YES] retain]; [runLoop run]; [pool release]; } I retain the timer, so I can easily invalidate and reschedule. Problem: I must also fire the run: method in response to GUI events, so it is synchronous (i.e. a "perform activity" button). Like this: [timer fire]; I could do this with performSelectorInBackground too, and of course it doesn't block the UI. But this synchronous firings run in another runloop! So I have no guarantee that they won't overlap. How can I queue all of my firings on the same runloop?

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• Guidelines for using Merge task in SSIS

  - by thursdaysgeek

  I have a table with three fields, one an identity field, and I need to add some new records from a source that has the other two fields. I'm using SSIS, and I think I should use the merge tool, because one of the sources is not in the local database. But, I'm confused by the merge tool and the proper process. I have my one source (an Oracle table), and I get two fields, well_id and well_name, with a sort after, sorting by well_id. I have the destination table (sql server), and I'm also using that as a source. It has three fields: well_key (identity field), well_id, and well_name, and I then have a sort task, sorting on well_id. Both of those are input to my merge task. I was going to output to a temporary table, and then somehow get the new records back into the sql server table. Oracle Well SQL Well | | V V Sort Source Sort Well | | -------> Merge* <----------- | V Temp well table I suspect this isn't the best way to use this tool, however. What are the proper steps for a merge like this? One of my reasons for questioning this method is that my merge has an error, telling me that the "Merge Input 2" must be sorted, but its source is a sort task, so it IS sorted. Example data SQL Well (before merge) well_key well_id well_name 1 123 well k 2 292 well c 3 344 well t 5 439 well d Oracle Well well_id well_name 123 well k 292 well c 311 well y 344 well t 439 well d 532 well j SQL Well (after merge) well_key well_id well_name 1 123 well k 2 292 well c 3 344 well t 5 439 well d 6 311 well y 7 532 well j Would it be better to load my Oracle Well to a temporary local file, and then just use a sql insert statment on it?

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• When does a PHP <5.3.0 daemon script receive signals?

  - by MidnightLightning

  I've got a PHP script in the works that is a job worker; its main task is to check a database table for new jobs, and if there are any, to act on them. But jobs will be coming in in bursts, with long gaps in between, so I devised a sleep cycle like: while(true) { if ($jobs = get_new_jobs()) { // Act upon the jobs } else { // No new jobs now sleep(30); } } Good, but in some cases that means there might be a 30 second lag before a new job is acted upon. Since this is a daemon script, I figured I'd try the pcntl_signal hook to catch a SIGUSR1 signal to nudge the script to wake up, like: $_isAwake = true; function user_sig($signo) { global $_isAwake; daemon_log("Caught SIGUSR1"); $_isAwake = true; } pcntl_signal(SIGUSR1, 'user_sig'); while(true) { if ($jobs = get_new_jobs()) { // Act upon the jobs } else { // No new jobs now daemon_log("No new jobs, sleeping..."); $_isAwake = false; $ts = time(); while(time() < $ts+30) { sleep(1); if ($_isAwake) break; // Did a signal happen while we were sleeping? If so, stop sleeping } $_isAwake = true; } } I broke the sleep(30) up into smaller sleep bits, in case a signal doesn't interrupt a sleep() command, thinking that this would cause at most a one-second delay, but in the log file, I'm seeing that the SIGUSR1 isn't being caught until after the full 30 seconds has passed (and maybe the outer while loop resets). I found the pcntl_signal_dispatch command, but that's only for PHP 5.3 and higher. If I were using that version, I could stick a call to that command before the if ($_isAwake) call, but as it currently stands I'm on 5.2.13. On what sort of situations is the signals queue interpreted in PHP versions without the means to explicitly call the queue parsing? Could I put in some other useless command in that sleep loop that would trigger a signal queue parse within there?

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• Record/Playback with AudioQueue on iPhone

  - by Biranchi

  Hi, I am currently using Audio Queues on the iPhone to record and playback audio. What I would like to be able to do is to record some audio, allow the user to pause the record queue, and to seek back and forward through the audio to select a position from where they can start recording from again. I have got over the seeking issue by making the playback AudioQueueBuffer sizes small enough so that the play audio queue callback happens at a rate that allows the user to use a slider control to hear the audio as they adjust the slider back and forth. I think I can achieve the recording at a new position by setting the inStartingPacket parameter of the AudioFileWritePackets function that I call from the Audio Recording Queue callback. The trouble is this only inserts audio over the previously recorded audio. The file length obviously doesn't change so if the user were to go backwards and record less audio than before, the old audio still remains after the end of the newly recorded audio. Is there a way I can get the AudioFile to truncate at the point the user starts to insert the new audio, is there some other way I can remove the old audio starting at the insert position or is there a better way about going about this task? Thanks

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• Seeking help with a MT design pattern

  - by SamG

  I have a queue of 1000 work items and a n-proc machine (assume n = 4).The main thread spawns n (=4) worker threads at a time ( 25 outer iterations) and waits for all threads to complete before processing the next n (=4) items until the entire queue is processed for(i= 0 to queue.Length / numprocs) for(j= 0 to numprocs) { CreateThread(WorkerThread,WorkItem) } WaitForMultipleObjects(threadHandle[]) The work done by each (worker) thread is not homogeneous.Therefore in 1 batch (of n) if thread 1 spends 1000 s doing work and rest of the 3 threads only 1 s , above design is inefficient,becaue after 1 sec other 3 processors are idling. Besides there is no pooling - 1000 distinct threads are being created How do I use the NT thread pool (I am not familiar enough- hence the long winded question) and QueueUserWorkitem to achieve the above. The following constraints should hold The main thread requires that all worker items are processed before it can proceed.So I would think that a waitall like construct above is required I want to create as many threads as processors (ie not 1000 threads at a time) Also I dont want to create 1000 distinct events, pass to the worker thread, and wait on all events using the QueueUserWorkitem API or otherwise Exisitng code is in C++.Prefer C++ because I dont know c# I suspect that the above is a very common pattern and was looking for input from you folks.

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• Does GC guarantee that cleared References are enqueued to ReferenceQueue in topological order?

  - by Dimitris Andreou

  Say there are two objects, A and B, and there is a pointer A.x --> B, and we create, say, WeakReferences to both A and B, with an associated ReferenceQueue. Assume that both A and B become unreachable. Intuitively B cannot be considered unreachable before A is. In such a case, do we somehow get a guarantee that the respective references will be enqueued in the intuitive (topological when there are no cycles) order in the ReferenceQueue? I.e. ref(A) before ref(B). I don't know - what if the GC marked a bunch of objects as unreachable, and then enqueued them in no particular order? I was reviewing Finalizer.java of guava, seeing this snippet: private void cleanUp(Reference<?> reference) throws ShutDown { ... if (reference == frqReference) { /* * The client no longer has a reference to the * FinalizableReferenceQueue. We can stop. */ throw new ShutDown(); } frqReference is a PhantomReference to the used ReferenceQueue, so if this is GC'ed, no Finalizable{Weak, Soft, Phantom}References can be alive, since they reference the queue. So they have to be GC'ed before the queue itself can be GC'ed - but still, do we get the guarantee that these references will be enqueued to the ReferenceQueue at the order they get "garbage collected" (as if they get GC'ed one by one)? The code implies that there is some kind of guarantee, otherwise unprocessed references could theoretically remain in the queue. Thanks

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• In C#, what thread will Events be handled in?

  - by Ben

  Hi, I have attempted to implement a producer/consumer pattern in c#. I have a consumer thread that monitors a shared queue, and a producer thread that places items onto the shared queue. The producer thread is subscribed to receive data...that is, it has an event handler, and just sits around and waits for an OnData event to fire (the data is being sent from a 3rd party api). When it gets the data, it sticks it on the queue so the consumer can handle it. When the OnData event does fire in the producer, I had expected it to be handled by my producer thread. But that doesn't seem to be what is happening. The OnData event seems as if it's being handled on a new thread instead! Is this how .net always works...events are handled on their own thread? Can I control what thread will handle events when they're raised? What if hundreds of events are raised near-simultaneously...would each have its own thread? Thank in advance! Ben

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• Semaphore race condition?

  - by poindexter12

  I have created a "Manager" class that contains a limited set of resources. The resources are stored in the "Manager" as a Queue. I initialize the Queue and a Semaphore to the same size, using the semaphore to block a thread if there are no resources available. I have multiple threads calling into this class to request a resource. Here is the psuedo code: public IResource RequestResource() { IResource resource = null; _semaphore.WaitOne(); lock (_syncLock) { resource = _resources.Dequeue(); } return resource; } public void ReleaseResource(IResource resource) { lock (_syncLock) { _resources.Enqueue(resource); } _semaphore.Release(); } While running this application, it seems to run fine for a while. Then, it seems like my Queue is giving out the same object. Does this seem like its possible? I'm pulling my hair out over here, and any help would be greatly appreciated. Feel free to ask for more information if you need it. Thanks!

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• Algorithm to determine which points should be visible on a map based on zoom

  - by lgratian

  Hi! I'm making a Google Maps-like application for a course at my Uni (not something complex, it should load the map of a city for example, not the whole world). The map can have many layers, including markers (restaurants, hospitals, etc.) The problem is that when you have many points and you zoom out the map it doesn't look right. At this zoom level only some points need to be visible (and at the maximum map size, all points). The question is: how can you determine which points should be visible for a specified zoom level? Because I have implemented a PR Quadtree to speed up rendering I thought that I could define some "high-priority" markers (that are always visible, defined in the map editor) and put them in a queue. At each step a marker is removed from the queue and all it's neighbors that are at least D units away (D depends on the zoom levels) are chosen and inserted in the queue, and so on. Is there any better way than the algorithm I thought of? Thanks in advance!

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• Blocking on DBCP connection pool (open and close connnection). Is database connection pooling in OpenEJB pluggable?

  - by topchef

  We use OpenEJB on Tomcat (used to run on JBoss, Weblogic, etc.). While running load tests we experience significant performance problems with handling JMS messages (queues). Problem was localized to blocking on database connection pool getting or releasing connection to the pool. Blocking prevented concurrent MDB instances (threads) from running hence performance suffered 10-fold and worse. The same code used to run on application servers (with their respective connection pool implementations) with no blocking at all. Example of thread blocked: Name: JMS Resource Adapter-worker-23 State: BLOCKED on org.apache.commons.pool.impl.GenericObjectPool@1ea6b4a owned by: JMS Resource Adapter-worker-19 Total blocked: 18,426 Total waited: 0 Stack trace: org.apache.commons.pool.impl.GenericObjectPool.returnObject(GenericObjectPool.java:916) org.apache.commons.dbcp.PoolableConnection.close(PoolableConnection.java:91) - locked org.apache.commons.dbcp.PoolableConnection@1bcba8 org.apache.commons.dbcp.managed.ManagedConnection.close(ManagedConnection.java:147) com.xxxxx.persistence.DbHelper.closeConnection(DbHelper.java:290) .... Couple of questions. I am almost certain that some transactional attributes and properties contribute to this blocking, but MDBs are defined as non-transactional (we use both annotations and ejb-jar.xml). Some EJBs do use container-managed transactions though (and we can observe blocking there as well). Are there any DBCP configurations that may fix blocking? Is DBCP connection pool implementation replaceable in OpenEJB? How easy (difficult) to replace it with another library? Just in case this is how we define data source in OpenEJB (openejb.xml): <Resource id="MyDataSource" type="DataSource"> JdbcDriver oracle.jdbc.driver.OracleDriver JdbcUrl ${oracle.jdbc} UserName ${oracle.user} Password ${oracle.password} JtaManaged true InitialSize 5 MaxActive 30 ValidationQuery SELECT 1 FROM DUAL TestOnBorrow true </Resource>

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• Why does my ActivePerl program report 'Sorry. Ran out of threads'?

  - by Zaid

  Tom Christiansen's example code (à la perlthrtut) is a recursive, threaded implementation of finding and printing all prime numbers between 3 and 1000. Below is a mildly adapted version of the script #!/usr/bin/perl # adapted from prime-pthread, courtesy of Tom Christiansen use strict; use warnings; use threads; use Thread::Queue; sub check_prime { my ($upstream,$cur_prime) = @_; my $child; my $downstream = Thread::Queue->new; while (my $num = $upstream->dequeue) { next unless ($num % $cur_prime); if ($child) { $downstream->enqueue($num); } else { $child = threads->create(\&check_prime, $downstream, $num); if ($child) { print "This is thread ",$child->tid,". Found prime: $num\n"; } else { warn "Sorry. Ran out of threads.\n"; last; } } } if ($child) { $downstream->enqueue(undef); $child->join; } } my $stream = Thread::Queue->new(3..shift,undef); check_prime($stream,2); When run on my machine (under ActiveState & Win32), the code was capable of spawning only 118 threads (last prime number found: 653) before terminating with a 'Sorry. Ran out of threads' warning. In trying to figure out why I was limited to the number of threads I could create, I replaced the use threads; line with use threads (stack_size => 1);. The resultant code happily dealt with churning out 2000+ threads. Can anyone explain this behavior?

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• "ImportError: cannot import name Exchange" when using Celery w/ Kombu installed

  - by alukach

  I'm trying to create a Celery worker node on an Amazon EC2 Windows2008 R2 instance. Due to a plugin we require for another Python module, we are required to user Python3. I've installed Python3.2 and necessary modules and run Celery, but for some reason it states that it can't import Exchange and Queue from Kombu, despite the face that Kombu is installed and can be imported by python. Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. All rights reserved. C:\Users\Administrator>celery Traceback (most recent call last): File "C:\Python32\Scripts\celery-script.py", line 9, in <module> load_entry_point('celery==3.0.11', 'console_scripts', 'celery')() File "C:\Python32\lib\site-packages\celery\__main__.py", line 13, in main from celery.bin.celery import main File "C:\Python32\lib\site-packages\celery\bin\celery.py", line 21, in <module> from celery.utils import term File "C:\Python32\lib\site-packages\celery\utils\__init__.py", line 22, in <module> from kombu import Exchange, Queue ImportError: cannot import name Exchange C:\Users\Administrator>python Python 3.2 (r32:88445, Feb 20 2011, 21:29:02) [MSC v.1500 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> from kombu import Exchange, Queue >>> print('WTF?!?') WTF?!? >>> This problem seems similar to this and this, but I have not been able to remedy the issue. Any ideas?

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• How to test a struts 2.1.x developer?

  - by Jason Pyeron

  We employ test to filter out those who can't. The tests are designed to be very low effort for those who can and too much effort for those who can't. Here is an example for java web application developer on an Oracle project: We only work with contractors who can use the tools we use, to determine if you can use the tools we have devised some very simple tests. Instructions If you are prepared and knowledgeable this will take you about 2-5 minutes. Suggested knowledge and tools: * subversion 1.6 see http://subversion.tigris.org/ or http://cygwin.com/setup.exe * java 1.6 see http://java.sun.com/javase/downloads/index.jsp * oracle >=10g see http://www.oracle.com/technology/software/products/jdev/index.html * j2ee server see http://tomcat.apache.org/download-55.cgi or http://www.jboss.org/jbossas/downloads/ Steps 1. check out svn://statics32.pdinc.us/home/subversion/guest 2. deploy the war file found at trunk/test.war 3. browse to the web application you installed from the war file and answer the one SQL question: How many rows are in the table 'testdata' where column 'value' ends with either an 'A' or an 'a'? The login credentials are in trunk/doc/oracle.txt 4. make a RESULTS HASH by submitting your answer to the form. 5. create a file in tmp/YourUserName.txt and put the RESULTS HASH in it, not the answer. 6. check in your file (don't forget to add the file first). 7. message me with the revision number of your check in. As such I am looking for ideas on how to test for someone to be a struts 2.1 w/ annotations.

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• XElement vs Dcitionary

  - by user135498

  Hi All, I need advice. I have application that imports 10,000 rows containing name & address from a text file into XElements that are subsequently added to a synchronized queue. When the import is complete the app spawns worker threads that process the XElements by deenqueuing them, making a database call, inserting the database output into the request document and inserting the processed document into an output queue. When all requests have been processed the output queue is written to disk as an XML doc. I used XElements for the requests because I needed the flexibility to add fields to the request during processing. i.e. Depending on the job type the app might require that it add phone number, date of birth or email address to a request based on a name/address match against a public record database. My questions is; The XElements seems to use quite a bit of memory and I know there is a lot of parsing as the document makes its way through the processing methods. I’m considering replacing the XElements with a Dictionary object but I’m skeptical the gain will be worth the effort. In essence it will accomplish the same thing. Thoughts?

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• ConcurrentLinkedQueue$Node remains in heap after remove()

  - by action8

  I have a multithreaded app writing and reading a ConcurrentLinkedQueue, which is conceptually used to back entries in a list/table. I originally used a ConcurrentHashMap for this, which worked well. A new requirement required tracking the order entries came in, so they could be removed in oldest first order, depending on some conditions. ConcurrentLinkedQueue appeared to be a good choice, and functionally it works well. A configurable amount of entries are held in memory, and when a new entry is offered when the limit is reached, the queue is searched in oldest-first order for one that can be removed. Certain entries are not to be removed by the system and wait for client interaction. What appears to be happening is I have an entry at the front of the queue that occurred, say 100K entries ago. The queue appears to have the limited number of configured entries (size() == 100), but when profiling, I found that there were ~100K ConcurrentLinkedQueue$Node objects in memory. This appears to be by design, just glancing at the source for ConcurrentLinkedQueue, a remove merely removes the reference to the object being stored but leaves the linked list in place for iteration. Finally my question: Is there a "better" lazy way to handle a collection of this nature? I love the speed of the ConcurrentLinkedQueue, I just cant afford the unbounded leak that appears to be possible in this case. If not, it seems like I'd have to create a second structure to track order and may have the same issues, plus a synchronization concern.

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• Getting a key in the ActionScript Dictionary

  - by Rudy

  Hello, I am using a Dictionary in ActionScript as a queue, sort of, still reading most of the time as an associative container, but I need one time to make a loop to run through the whole dictionary, such as for (var key:String in queue) . Inside this for loop I perform some actions on an element and then call delete on that key. My issue is that I would like to wait for an Event before fetching the next element in this queue. Basically my for loop runs too fast. I would like to fetch the next key all the time, but I know there is no built in method. A solution I thought is to add a break to the loop, as the for.. in will automatically fetch the next key, but it would be a loop which always executes one time, simply to fetch the next key. This sounds a bit counter intuitive. I hope my problem makes sense and I really look for some better ideas than what I currently have. Thanks for your help! Rudy

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• What is the best way to use Guice and JMock together?

  - by Yishai

  I have started using Guice to do some dependency injection on a project, primarily because I need to inject mocks (using JMock currently) a layer away from the unit test, which makes manual injection very awkward. My question is what is the best approach for introducing a mock? What I currently have is to make a new module in the unit test that satisfies the dependencies and bind them with a provider that looks like this: public class JMockProvider<T> implements Provider<T> { private T mock; public JMockProvider(T mock) { this.mock = mock; } public T get() { return mock; } } Passing the mock in the constructor, so a JMock setup might look like this: final CommunicationQueue queue = context.mock(CommunicationQueue.class); final TransactionRollBack trans = context.mock(TransactionRollBack.class); Injector injector = Guice.createInjector(new AbstractModule() { @Override protected void configure() { bind(CommunicationQueue.class).toProvider(new JMockProvider<QuickBooksCommunicationQueue>(queue)); bind(TransactionRollBack.class).toProvider(new JMockProvider<TransactionRollBack>(trans)); } }); context.checking(new Expectations() {{ oneOf(queue).retrieve(with(any(int.class))); will(returnValue(null)); never(trans); }}); injector.getInstance(RunResponse.class).processResponseImpl(-1); Is there a better way? I know that AtUnit attempts to address this problem, although I'm missing how it auto-magically injects a mock that was created locally like the above, but I'm looking for either a compelling reason why AtUnit is the right answer here (other than its ability to change DI and mocking frameworks around without changing tests) or if there is a better solution to doing it by hand.

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