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• Thread to receive the messages from serial port is not working using c#

  - by karthik

  I am using Serial port to receive the messages. The below function is running in a thread. When i debug i find that the thread is running properly. But "if (sp.IsOpen)" is always false, due to which the code is not executing inside the IF condition at all. It says the Port is closed. I will be having multiple serial ports in my system and i will not know, which port will receive the message. So i need to listen to all the ports in one Thread. How can i solve my problem here ? private void ListenerPorts() { log.Info("Listening Thread Started"); while (true) { //foreach (SerialPort sp in storeport) foreach (SerialPort sp in comPortsList) { if (sp.IsOpen) { sp.ReadTimeout = readTimeoutInMs; sp.WriteTimeout = writeTimeoutInMs; try { string msg = sp.ReadLine(); this.GetMessageRichTextBox("Message : " + msg + "\n"); sp.WriteLine(sp.PortName); if (msg.Contains("COM")) { // is AutoScan receiverPortName = sp.ReadLine(); this.updateLblStatusRichTextBox(sp.PortName + " is connected to " + msg + "\n"); } else { //standalone is uppercase ReceiverPortName = sp.ReadLine(); this.updateLblStatusRichTextBox(sp.PortName + " is connected to " + ReceiverPortName + "\n"); } } catch (Exception ex) { // no data System.Diagnostics.Debug.WriteLine(sp.PortName + " : " + ex.Message); } } } } }

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• Is Stream.Write thread-safe?

  - by Mike Spross

  I'm working on a client/server library for a legacy RPC implementation and was running into issues where the client would sometimes hang when waiting to a receive a response message to an RPC request message. It turns out the real problem was in my message framing code (I wasn't handling message boundaries correctly when reading data off the underlying NetworkStream), but it also made me suspicious of the code I was using to send data across the network, specifically in the case where the RPC server sends a large amount of data to a client as the result of a client RPC request. My send code uses a BinaryWriter to write a complete "message" to the underlying NetworkStream. The RPC protocol also implements a heartbeat algorithm, where the RPC server sends out PING messages every 15 seconds. The pings are sent out by a separate thread, so, at least in theory, a ping can be sent while the server is in the middle of streaming a large response back to a client. Suppose I have a Send method as follows, where stream is a NetworkStream: public void Send(Message message) { //Write the message to a temporary stream so we can send it all-at-once MemoryStream tempStream = new MemoryStream(); message.WriteToStream(tempStream); //Write the serialized message to the stream. //The BinaryWriter is a little redundant in this //simplified example, but here because //the production code uses it. byte[] data = tempStream.ToArray(); BinaryWriter bw = new BinaryWriter(stream); bw.Write(data, 0, data.Length); bw.Flush(); } So the question I have is, is the call to bw.Write (and by implication the call to the underlying Stream's Write method) atomic? That is, if a lengthy Write is still in progress on the sending thread, and the heartbeat thread kicks in and sends a PING message, will that thread block until the original Write call finishes, or do I have to add explicit synchronization to the Send method to prevent the two Send calls from clobbering the stream?

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• cancelPreviousPerformRequestWithTarget is not canceling my previously delayed thread started with pe

  - by jmurphy

  Hello, I've launched a delayed thread using performSelector but the user still has the ability to hit the back button on the current view causing dealloc to be called. When this happens my thread still seems to be called which causes my app to crash because the properties that thread is trying to write to have been released. To solve this I am trying to call cancelPreviousPerformRequestsWithTarget to cancel the previous request but it doesn't seem to be working. Below are some code snippets. - (void) viewDidLoad { [self performSelector:@selector(myStopUpdatingLocation) withObject:nil afterDelay:6]; } (void)viewWillDisappear:(BOOL)animated { [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(myStopUpdatingLocation) object:nil]; } Am I doing something incorrect here? The method myStopUpdatingLocation is defined in the same class that I'm calling the perform requests. A little more background. The function that I'm trying to implement is to find a users location, search google for some locations around that location and display several annotations on the map. On viewDidLoad I start updating the location with CLLocationManager. I've build in a timeout after 6 seconds if I don't get my desired accuracy within the timeout and I'm using a performSelector to do this. What can happen is the user clicks the back button in the view and this thread will still execute even though all my properties have been released causing a crash. Thanks in advance! James

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• different thread accessing MemoryStream

  - by Wayne

  There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately. This code works purposes 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem is that the memory.Position property suddenly returns zero instead of the appropriate value. However, code was added that checks for the 0 and throws an exception which include log of the MemoryStream properties like Position and Length in a separate method. Those return the correct value. Further addition shows that when this rare condition occurs, the memory.Position only has zero inside this particular method. Okay. Obviously, this must be a threading issue. But this code is well locked. However, the nature of this software is that it's organized by "tasks" with a scheduler and so any one of several actual O/S thread may run this code at any give time--but never more than one at a time. So it's my guess that ordinarily it so happens that the same thread keeps getting used for this method and then on a rare occasion a different thread get used. Then due to compiler optimizations, the different thread never gets the correct value. It gets a "stale" value. Ordinarily in a situation like this I would apply a "volatile" keyword to the variable in question. But that (those) variables are inside the MemoryStream object. Does anyone have any other idea? Or does this mean we have to implement our own MemoryStream object? (Just like we end up having to do with practically every collection in .NET?) It's a shame to have such an awesome platform as .NET and have virtually the entire system useless as-is for seriously parallelized applications. If I'm wrong or you have other ideas, please advise. Sincerely, Wayne

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• Terminal-based snake game: input thread manipulates output

  - by enlightened

  I'm writing a snake game for the terminal, i.e. output via print. The following works just fine: while status[snake_monad] do print to_string draw canvas, compose_all([ frame, specs, snake_to_hash(snake[snake_monad]) ]) turn! snake_monad, get_dir move! snake_monad, specs sleep 0.25 end But I don't want the turn!ing to block, of course. So I put it into a new Thread and let it loop: Thread.new do loop do turn! snake_monad, get_dir end end while status[snake_monad] do ... # no turn! here ... end Which also works logically (the snake is turning), but the output is somehow interspersed with newlines. As soon as I kill the input thread (^C) it looks normal again. So why and how does the thread have any effect on my output? And how do I work around this issue? (I don't know much about threads, even less about them in ruby. Input and output concurrently on the same terminal make the matter worse, I guess...) Also (not really important): Wanting my program as pure as possible, would it be somewhat easily possible to get the input non-blockingly while passing everything around? Thank you!

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• Thread mutex behaviour

  - by Alberteddu

  Hi there, I'm learning C. I'm writing an application with multiple threads; I know that when a variable is shared between two or more threads, it is better to lock/unlock using a mutex to avoid deadlock and inconsistency of variables. This is very clear when I want to change or view one variable. int i = 0; /** Global */ static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /** Thread 1. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); /** Thread 2. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); This is correct, I think. The variable i, at the end of the executions, contains the integer 2. Anyway, there are some situations in which I don't know exactly where to put the two function calls. For example, suppose you have a function obtain(), which returns a global variable. I need to call that function from within the two threads. I have also two other threads that call the function set(), defined with a few arguments; this function will set the same global variable. The two functions are necessary when you need to do something before getting/setting the var. /** (0) */ /** Thread 1, or 2, or 3... */ if(obtain() == something) { if(obtain() == somethingElse) { // Do this, sometimes obtain() and sometimes set(random number) (1) } else { // Do that, just obtain(). (2) } } else { // Do this and do that (3) // If # of thread * 3 > 10, then set(3*10) For example. (4) } /** (5) */ Where I have to lock, and where I have to unlock? The situation can be, I think, even more complex. I will appreciate an exhaustive answer. Thank you in advance. —Alberto

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• Creating Thread in Win32

  - by Dave18

  Does ThreadFunc() gets called two times here? sometimes I notice a single call and sometimes none at all. #include <windows.h> #include <stdio.h> DWORD WINAPI ThreadFunc(LPVOID); int main() { HANDLE hThread; DWORD threadld; hThread = CreateThread(NULL, 0, ThreadFunc, 0, 0, &threadld ); printf("Thread is running\n"); } DWORD WINAPI ThreadFunc(LPVOID p) { printf("In ThreadFunc\n"); return 0; } Output 1 Thread is running In ThreadFunc In ThreadFunc Press any key to continue . . . Output 2 Thread is running In ThreadFunc Press any key to continue . . . Output 3 Thread is running Press any key to continue . . .

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• Strange thread behavior in Perl

  - 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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• how to slove error when using thread?

  - by ChandreshKanetiya

  I have following error msg in console when using NSThread "Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now..." I have submit my sample code here - (void)viewDidLoad { appDeleg = (NewAshley_MedisonAppDelegate *)[[UIApplication sharedApplication] delegate]; [[self tblView1] setRowHeight:80.0]; [super viewDidLoad]; self.title = @"Under Ground"; [UIApplication sharedApplication].networkActivityIndicatorVisible = YES; [NSThread detachNewThreadSelector:@selector(CallParser) toTarget:self withObject:nil]; } -(void)CallParser { Parsing *parsing = [[Parsing alloc] init]; [parsing DownloadAndParseUnderground]; [parsing release]; [self Update_View]; //[myIndicator stopAnimating]; [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; } here "DownloadAndParseUnderground" is the method of downloding data from the rss feed and -(void) Update_View{ [self.tblView1 reloadData]; } when Update_View method is called the tableView reload Data and in the cellForRowAtIndexPath create error and not display custom cell - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; CustomTableviewCell *cell = (CustomTableviewCell *) [tblView1 dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { [[NSBundle mainBundle] loadNibNamed:@"customCell" owner:self options:nil]; cell = objCustCell; objCustCell = nil; }

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• Accessing Instance Attributes from Secondary Thread (iPhone-SDK)

  - by Travis

  I have a class with an NSDictionary attribute. Inside this class I dispatch another thread to handle NSXMLParser handling. Inside my -didStartElement, I access the dictionary in the class (to compare an element found in the XML to one in the dictionary). At this point I get undefined results. Using NSLog (I'm not advanced in XCode debugging), I see that it bombs around access of the NSDictionary. I tried just iterating the dictionary and dumping the key/values inside the didStartElement and this bombs at different keys each time. The only thing I can conclude is that something is not kosher that I'm doing with regards to accessing main thread attributes from the secondary thread. I'm somewhat new to multithreading and am not sure what the best protocol is safely access attributes from additional threads. Thanks all.

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• Oracle Linux and Oracle VM pricing guide

  - by wcoekaer

  A few days ago someone showed me a pricing guide from a Linux vendor and I was a bit surprised at the complexity of it. Especially when you look at larger servers (4 or 8 sockets) and when adding virtual machine use into the mix. I think we have a very compelling and simple pricing model for both Oracle Linux and Oracle VM. Let me see if I can explain it in 1 page, not 10 pages. This pricing information is publicly available on the Oracle store, I am using the current public list prices. Also keep in mind that this is for customers using non-oracle x86 servers. When a customer purchases an Oracle x86 server, the annual systems support includes full use (all you can eat) of Oracle Linux, Oracle VM and Oracle Solaris (no matter how many VMs you run on that server, in case you deploy guests on a hypervisor). This support level is the equivalent of premier support in the list below. Let's start with Oracle VM (x86) : Oracle VM support subscriptions are per physical server on which you deploy the Oracle VM Server product. (1) Oracle VM Premier Limited - 1- or 2 socket server : $599 per server per year (2) Oracle VM Premier - more than 2 socket server (4, or 8 or whatever more) : $1199 per server per year The above includes the use of Oracle VM Manager and Oracle Enterprise Manager Cloud Control's Virtualization management pack (including self service cloud portal, etc..) 24x7 support, access to bugfixes, updates and new releases. It also includes all options, live migrate, dynamic resource scheduling, high availability, dynamic power management, etc If you want to play with the product, or even use the product without access to support services, the product is freely downloadable from edelivery. Next, Oracle Linux : Oracle Linux support subscriptions are per physical server. If you plan to run Oracle Linux as a guest on Oracle VM, VMWare or Hyper-v, you only have to pay for a single subscription per system, we do not charge per guest or per number of guests. In other words, you can run any number of Oracle Linux guests per physical server and count it as just a single subscription. (1) Oracle Linux Network Support - any number of sockets per server : $119 per server per year Network support does not offer support services. It provides access to the Unbreakable Linux Network and also offers full indemnification for Oracle Linux. (2) Oracle Linux Basic Limited Support - 1- or 2 socket servers : $499 per server per year This subscription provides 24x7 support services, access to the Unbreakable Linux Network and the Oracle Support portal, indemnification, use of Oracle Clusterware for Linux HA and use of Oracle Enterprise Manager Cloud control for Linux OS management. It includes ocfs2 as a clustered filesystem. (3) Oracle Linux Basic Support - more than 2 socket server (4, or 8 or more) : $1199 per server per year This subscription provides 24x7 support services, access to the Unbreakable Linux Network and the Oracle Support portal, indemnification, use of Oracle Clusterware for Linux HA and use of Oracle Enterprise Manager Cloud control for Linux OS management. It includes ocfs2 as a clustered filesystem (4) Oracle Linux Premier Limited Support - 1- or 2 socket servers : $1399 per server per year This subscription provides 24x7 support services, access to the Unbreakable Linux Network and the Oracle Support portal, indemnification, use of Oracle Clusterware for Linux HA and use of Oracle Enterprise Manager Cloud control for Linux OS management, XFS filesystem support. It also offers Oracle Lifetime support, backporting of patches for critical customers in previous versions of package and ksplice zero-downtime updates. (5) Oracle Linux Premier Support - more than 2 socket servers : $2299 per server per year This subscription provides 24x7 support services, access to the Unbreakable Linux Network and the Oracle Support portal, indemnification, use of Oracle Clusterware for Linux HA and use of Oracle Enterprise Manager Cloud control for Linux OS management, XFS filesystem support. It also offers Oracle Lifetime support, backporting of patches for critical customers in previous versions of package and ksplice zero-downtime updates. (6) Freely available Oracle Linux - any number of sockets You can freely download Oracle Linux, install it on any number of servers and use it for any reason, without support, without right to use of these extra features like Oracle Clusterware or ksplice, without indemnification. However, you do have full access to all errata as well. Need support? then use options (1)..(5) So that's it. Count number of 2 socket boxes, more than 2 socket boxes, decide on basic or premier support level and you are done. You don't have to worry about different levels based on how many virtual instance you deploy or want to deploy. A very simple menu of choices. We offer, inclusive, Linux OS clusterware, Linux OS Management, provisioning and monitoring, cluster filesystem (ocfs), high performance filesystem (xfs), dtrace, ksplice, ofed (infiniband stack for high performance networking). No separate add-on menus. NOTE : socket/cpu can have any number of cores. So whether you have a 4,6,8,10 or 12 core CPU doesn't matter, we count the number of physical CPUs.

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• Algorithm to determine thread "hotness"

  - by nickf

  I'm trying to come up with a way to determine how "hot" certain threads are in a forum. What criteria would you use and why? How would these come together to give a hotness score? The criteria I'm thinking of include: how many replies how long since the last reply average time between replies The problems this algorithm must solve: A thread which has 500 replies is clearly hot, unless the last reply was over a year ago. A thread with 500 replies that was replied to a second ago is clearly hot, unless it's taken 4 years to reach 500 replies. A thread with 15 replies in the last 4 minutes is really hot! Any ideas, thoughts or complete solutions out there?

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• Creating an independent draw thread using pthreads (C++)

  - by sagekilla

  Hi all, I'm working on a graphical application which looks something like this: while (Simulator.simulating) { Simulator.update(); InputManager.processInput(); VideoManager.draw(); } I do this several times a second, and in the vast majority of cases my computation will be taking up 90 - 99% of my processing time. What I would like to do is take out the processInput and draw functions and have each one run independently. That way, I can have the input thread always checking for input (at a reasonable rate), and the draw thread attempting to redraw at a given frame rate. My issue is I'm not sure how I can properly do this. How would I properly initialize my pthread_t and associated pthread_attr_t so that the thread runs without blocking what I'm doing? Any help or even a link is appreciated, thanks!

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• No Hibernate Session bound to thread grails

  - by naresh

  Actually we've lot of quartz jobs in our application. For some time all of the jobs work fine. After some time all jobs are throwing the following exception. org.quartz.JobExecutionException: No Hibernate Session bound to thread, and configuration does not allow creation of non-transactional one here [See nested exception: java.lang.IllegalStateException: No Hibernate Session bound to thread, and configuration does not allow creation of non-transactional one here] at grails.plugins.quartz.QuartzDisplayJob.execute(QuartzDisplayJob.groovy:37) at org.quartz.core.JobRunShell.run(JobRunShell.java:202) at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573) Caused by: java.lang.IllegalStateException: No Hibernate Session bound to thread, and configuration does not allow creation of non-transactional one here at grails.plugins.quartz.QuartzDisplayJob.execute(QuartzDisplayJob.groovy:29) ... 2 more

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• Why Does Thread.CurrentThread.CurrentCulture Change between Page Rendering and HttpModule.PostReques

  - by Chad

  I'm creating an HttpModule that needs to know the value of Thread.CurrentThread.CurrentCulture as set in an MVC application. That value is currently being set by the BaseController, but when my HttpModule.PostRequestHandlerExecute() method fires, it reverts to what the Culture was prior to page rendering. I have duplicated this by creating a simple web app with these steps: Module.PreRequestHandlerExecute: Set culture to A Page_Load: Culture is currently A. Set culture to B Module.PostRequestHandlerExecute: Current thread culture is A. I expected it to be B but it was changed between page rendering and PostRequestHandlerExecute Any idea why .Net changes this value or how I could get around it? The thread is the same, so something in .Net must be explicitly reverting the culture.

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• DataTable.WriteXml on background thread

  - by Sheraz KHan

  I am trying to serealize DataTables in a background thread and it's failing. Any idea [Test] public void Async_Writing_DataTables() { string path = @"C:\Temp\SerialzeData"; if (!Directory.Exists(path)) { Directory.CreateDirectory(path); } Assert.IsTrue(Directory.Exists(path)); Thread thread1 = new Thread(new ThreadStart(delegate { object lockObject = new object(); for (int index = 0; index < 10; index++) { lock (lockObject) { DataTable table = new DataTable("test"); table.WriteXml(Path.Combine(path, table.TableName + index + ".xml")); } } })); thread1.Start(); }

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• How to simulate different CPU frequency and limit RAM

  - by user351103

  Hi I have to build a simulator with C#. This simulator should be able to run a second thread with configureable CPU speed and limited RAM size, e.g. 144MHz and 50 MB. Of course I know that a simulator can never be as accurate as the real hardware. But I try to get almost similar performance. At the moment I'm thinking about creating a thread which I will stop/sleep from time to time. Depending on the desired CPU speed the simulator should adjust the sleep time of this thread and therefore simulate different cpu frequency. To measure the achieved speed I though about using PerformanceCounters. But with this approach I have the problem that I don't know how to limit the RAM size the thread could use. Do you have any ideas how to realize such a simulator? Thanks in advance!!

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• Multithreaded program in C: calculating thread stack space

  - by SlappyTheFish

  Situation: I am writing a program in C that maintains a number of threads. Once a thread ends, a new one is created. Each thread forks - the child runs a PHP process via exec() and the parent waits for it to finish. Each PHP process takes the next item from a queue, processes it and exits. Basic code: http://www.4pmp.com/2010/03/multitasking-php-in-parallel/ Problem: The PHP processes are Symfony tasks and Symfony requires a fairly huge amount of memory. How can I safely calculate the required stack space for each thread so that PHP processes will have enough memory? The memory limit set in php.ini is 128Mb so should I allocate this much space in the stack?

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• Controllers and threads

  - by user72185

  Hi, I'm seeing this code in a project and I wonder if it is safe to do: (ASP.NET MVC 2.0) class MyController { void ActionResult SomeAction() { System.Threading.Thread newThread = new System.Threading.Thread(AsyncFunc); newThread.Start(); } void AsyncFunc() { string someString = HttpContext.Request.UrlReferrer.Authority + Url.Action("Index", new { controller = "AnotherAction" } ); } } Is the controller reused, possibly changing the content of HttpContext.Request and Url, or is this fine (except for not using the thread pool). Thanks for info!

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• BackgroundWorker vs background Thread

  - by freddy smith

  I have a stylistic question about the choice of background thread implementation I should use on a windows form app. Currently I have a BackgroundWorker on a form that has an infinite (while(true)) loop. In this loop I use WaitHandle.WaitAny to keep the thread snoozing until something of interest happens. One of the event handles I wait on is a "stopthread" event so that I can break out of the loop. This event is signaled when from my overridden Form.Dispose(). I read somewhere that BackgroundWorker is really intended for operations that you dont want to tie up the UI with and have an finite end - like downloading a file, or processing a sequence of items. In this case the "end" is unknown and only when the window is closed. Therefore would it be more appropriate for me to use a background Thread instead of BackgroundWorker for this purpose?

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• How to re-use a thread in Java ?

  - by David

  I am a building a console Sudoku Solver where the main objective is raw speed. I now have a ManagerThread that starts WorkerThreads to compute the neibhbors of each cell. So one WorkerThread is started for each cell right now. How can I re-use an existing thread that has completed its work? The Thread Pool Pattern seems to be the solution, but I don't understand what to do to prevent the thread from dying once its job has been completed. ps : I do not expect to gain much performance for this particular task, just want to experiment how multi-threading works before applying it to the more complex parts of the code. Thanks

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• Android - Question on postDelayed and Threads

  - by Chris

  I have a question about postDelayed. The android docs say that it adds the runnable to the queue and it runs in the UI thread. What does this mean? So, for example, the same thread I use to create my layout is used to run the Runnable? What if I want it as an independent thread that executes while I am creating my layout and defining my activity? Thanks Chris

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• How to pause a thread in java?

  - by mithun1538

  Consider the following code: while(true) { someFunction(); Thread.sleep(1000); } What I want is that, someFunction() be called once every 10 seconds. But this is not the case. It is being called every second. I tried Thread.wait(1000), but even that doesnt help. I removed of the while part, just kept the body, and at the end wrote : Thread.start(); But it throwed an exception. Is there any other solution to this?

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• Am I correct in my assumption about synchronized block?

  - by kunjaan

  I have a method shout() with a synchronized block. private void shout(){ System.out.println("SHOUT " + Thread.currentThread().getName()); synchronized(this){ System.out.println("Synchronized Shout" + Thread.currentThread().getName()); try { Thread.sleep(50); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Synchronized Shout" + Thread.currentThread().getName()); } } If I have two Threads that run this method, am I correct in assuming that the two "Synchronized Shout" will always appear one after the other? There can be no other statements in between the "Synchronized Shout"?

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• Accidental Complexity in OpenSSL HMAC functions

  - by Hassan Syed

  SSL Documentation Analaysis This question is pertaining the usage of the HMAC routines in OpenSSL. Since Openssl documentation is a tad on the weak side in certain areas, profiling has revealed that using the: unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len, const unsigned char *d, int n, unsigned char *md, unsigned int *md_len); From here, shows 40% of my library runtime is devoted to creating and taking down **HMAC_CTX's behind the scenes. There are also two additional function to create and destroy a HMAC_CTX explicetly: HMAC_CTX_init() initialises a HMAC_CTX before first use. It must be called. HMAC_CTX_cleanup() erases the key and other data from the HMAC_CTX and releases any associated resources. It must be called when an HMAC_CTX is no longer required. These two function calls are prefixed with: The following functions may be used if the message is not completely stored in memory My data fits entirely in memory, so I choose the HMAC function -- the one whose signature is shown above. The context, as described by the man page, is made use of by using the following two functions: HMAC_Update() can be called repeatedly with chunks of the message to be authenticated (len bytes at data). HMAC_Final() places the message authentication code in md, which must have space for the hash function output. The Scope of the Application My application generates a authentic (HMAC, which is also used a nonce), CBC-BF encrypted protocol buffer string. The code will be interfaced with various web-servers and frameworks Windows / Linux as OS, nginx, Apache and IIS as webservers and Python / .NET and C++ web-server filters. The description above should clarify that the library needs to be thread safe, and potentially have resumeable processing state -- i.e., lightweight threads sharing a OS thread (which might leave thread local memory out of the picture). The Question How do I get rid of the 40% overhead on each invocation in a (1) thread-safe / (2) resume-able state way ? (2) is optional since I have all of the source-data present in one go, and can make sure a digest is created in place without relinquishing control of the thread mid-digest-creation. So, (1) can probably be done using thread local memory -- but how do I resuse the CTX's ? does the HMAC_final() call make the CTX reusable ?. (2) optional: in this case I would have to create a pool of CTX's. (3) how does the HMAC function do this ? does it create a CTX in the scope of the function call and destroy it ? Psuedocode and commentary will be useful.

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