[libdispatch-dev] Memory issues with libdispatch

[Daniel A. Steffen]

Aldrin,

how are you measuring this memory usage growth? I cannot reproduce it on Mac OS X with the 'heap' tool

You might be seeing the temporary effects of the libdispatch continuation cache, these are small buffers that get allocated for each dispatch_async() and cached on a per-thread basis for speed. That cache is freed once a temporary dispatch worker thread exits ( a couple of seconds after SIGHUP in your example, on Mac OS X at least)

Also note that there is no need to dispatch_async() from your source event handler since you are already on the main queue at that point (the target queue of the source)

Daniel

On Apr 29, 2012, at 23:09, Aldrin Martoq Ahumada <aldrin.martoq at gmail.com> wrote:

> Hi, I have been testing sample code from the wiki and found that libdispatch is alloc'ing a lot of memory without releasing it, both in OS X (Lion 10.7.3, Xcode 4.3.2) and Linux (manually compiled and installed).
> 
> The code creates a SIGHUP signal source, with a handler that calls 100_000 writes to a logfile. The write to a log is queued in a serial queue.
> 
> The first run shows normal memory usage (8-9 MiB both Linux and OS X). After sending a "kill -1 <pid>" memory usage increases 1-20MiB every time I send the SIGHUP signal.
> 
> I have tried compiling with -fobj-arc and without it, but the result is the same. I removed the NSString usage in the br_log function, but the leak is not there: it is somewhere inside libdispatch.
> 
> I tried both valgrind and Xcode Instruments, but no leaks are found. Thanks in advance,
> 
> 
> ---- ini ----
> //
> //  main.m
> //  test02
> //
> //  Created by Aldrin Martoq on 4/29/12.
> //  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
> //
> 
> #include <unistd.h>
> #import <Foundation/Foundation.h>
> #import <dispatch/dispatch.h>
> 
> static FILE *log_file = NULL;
> static NSString *log_filename = @"/tmp/br.log";
> static dispatch_queue_t log_queue;
> 
> 
> void br_log(NSString *format, ...) {
>     @autoreleasepool {
>         va_list ap;
>         va_start(ap, format);
>         NSString *s = [[NSString alloc] initWithFormat:format arguments:ap];
>         va_end(ap);
>         
>         if (log_file == NULL) {
>             log_queue = dispatch_queue_create("cl.martoq.log_queue", NULL);
>             
>             log_file = fopen([log_filename cStringUsingEncoding:NSUTF8StringEncoding], "a");
>             NSLog(@"Log file created: %@", log_filename);
>         }
>         
>         dispatch_async(log_queue, ^{
>             @autoreleasepool {
>                 const char *c = [s cStringUsingEncoding:NSUTF8StringEncoding];
>                 fputs(c, log_file);
>                 fputs("\n", log_file);
>                 fflush(log_file);
>                 [s release];
>             }
>         });
>     }
> }
> 
> void br_setup() {
>     signal(SIGHUP, SIG_IGN);
>     dispatch_source_t sig_src = dispatch_source_create(DISPATCH_SOURCE_TYPE_SIGNAL, SIGHUP, 0, dispatch_get_main_queue());
>     dispatch_source_set_event_handler(sig_src, ^{
>         dispatch_async(dispatch_get_main_queue(), ^{
>             printf("Caught SIGHUP\n");
>             for (int i = 0; i < 100000; i++) {
>                 br_log(@"prueba: %d", i);
>             }
>         });
>     });
>     dispatch_resume(sig_src);
> }
> 
> 
> int main(int argc, const char * argv[]) {
>     @autoreleasepool {
>         // insert code here...
>         NSLog(@"Hello, World!");
>         br_setup();
>         dispatch_main();
>     }
>     return 0;
> }
> ---- fini ----
> 
> 
> 
> Aldrin Martoq A.
> http://aldrin.martoq.cl/
> 
> _______________________________________________
> libdispatch-dev mailing list
> libdispatch-dev at lists.macosforge.org
> http://lists.macosforge.org/mailman/listinfo.cgi/libdispatch-dev

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