XS: free() outside of the main thread causes crash on Windows

OlegG has asked for the wisdom of the Perl Monks concerning the following question:

Crash occures only on Windows.
Here is a simple example

My.xs

#include <pthread.h>
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "ppport.h"

void *thread(void *arg) {
    char *msg = (char*)arg;
    printf("thread: %s\n", msg);
    free(msg);
    return NULL;
}

MODULE = My    PACKAGE = My

void
test_thread(char *msg)
    PPCODE:
        char *thread_arg = malloc((strlen(msg)+1)*sizeof(char));
        strcpy(thread_arg, msg);
        pthread_t tid;
        pthread_create(&tid, NULL, thread, (void*)thread_arg);
        
        void *rv;
        pthread_join(tid, &rv);
[download]

lib/My.pm

package My;

use strict;
use XSLoader();
our $VERSION = 0.01;

XSLoader::load('My', $VERSION);

1;
[download]

Makefile.PL

use ExtUtils::MakeMaker;

WriteMakefile(
    NAME           => 'My',
    VERSION_FROM   => 'lib/My.pm',
    LIBS           => ['-lpthread'],
);
[download]

t.pl

use blib;
use My;

My::test_thread("Just another XS hacker");
[download]

This works on Linux and crashes on Windows. If I'll comment free(msg) it will also work on Windows.
What's wrong here?

UPD:
All files of the example in one place: https://github.com/olegwtf/sandbox/tree/master/xs-free-windows-problem

Comment on XS: free() outside of the main thread causes crash on Windows Select or Download Code

Replies are listed 'Best First'.
Re: XS: free() outside of the main thread causes crash on Windows by BrowserUk (Patriarch) on Sep 25, 2014 at 07:01 UTC
This works on Linux and crashes on Windows. I'm very surprised that it even builds on Windows given that Windows doesn't support pthreads. How is it resolving `#include <pthread.h>`; and therefore `pthread_create()` & `pthread_join()`? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^2: XS: free() outside of the main thread causes crash on Windows by OlegG (Monk) on Sep 25, 2014 at 07:21 UTC
Some perl distributions for windows includes pthreads-win32 implementation of pthreads. Strawberry Perl, I think. And for others I built pthreads-win32 myself and changed Makefile.PL a little bit. You can find fully compilable version for both windows and others OS here: https://github.com/olegwtf/sandbox/tree/master/xs-free-windows-problem	[reply]
Re^3: XS: free() outside of the main thread causes crash on Windows by BrowserUk (Patriarch) on Sep 25, 2014 at 07:32 UTC
I strongly suggest that you should compile your code with /E or equivalent to produce the post-preprocessor code and take a look at what is actually being call for malloc() and free(); because it almost certainly isn't the appropriate CRT routines. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^4: XS: free() outside of the main thread causes crash on Windows by OlegG (Monk) on Sep 25, 2014 at 07:56 UTC
Re^5: XS: free() outside of the main thread causes crash on Windows by BrowserUk (Patriarch) on Sep 25, 2014 at 08:32 UTC
Re^5: XS: free() outside of the main thread causes crash on Windows by Anonymous Monk on Sep 25, 2014 at 08:07 UTC
Some notes below your chosen depth have not been shown here
Re^4: XS: free() outside of the main thread causes crash on Windows by Anonymous Monk on Sep 25, 2014 at 07:58 UTC
Re^5: XS: free() outside of the main thread causes crash on Windows by BrowserUk (Patriarch) on Sep 25, 2014 at 08:41 UTC
Some notes below your chosen depth have not been shown here
Re^3: XS: free() outside of the main thread causes crash on Windows by Anonymous Monk on Sep 25, 2014 at 07:26 UTC
Have you heard of perlclib? It advocates using Newx() and Safefree() instead of malloc/free	[reply]
Re^4: XS: free() outside of the main thread causes crash on Windows by OlegG (Monk) on Sep 25, 2014 at 07:45 UTC
Re^2: XS: free() outside of the main thread causes crash on Windows (mingw) by Anonymous Monk on Sep 25, 2014 at 07:09 UTC
mingw as always `citrusperl\mingw\mingw32\pthreads-win32\i686-w64-mingw32\lib\libpthrea +d.a citrusperl\mingw\mingw32\pthreads-win32\i686-w64-mingw32\include\pthre +ad.h` [download]	[reply] [d/l]
Re: XS: free() outside of the main thread causes crash on Windows by syphilis (Archbishop) on Sep 25, 2014 at 08:43 UTC
For standalone testing purposes, you can run this as an Inline::C script: use strict; use warnings; use Inline C => Config => USING => 'ParseRegExp', BUILD_NOISY => 1, ; use Inline C => <<'EOC'; #include <pthread.h> void thread(void arg) { char msg = (char)arg; printf("thread: %s\n", msg); free(msg); return NULL; } void test_thread(char msg) { char thread_arg = malloc((strlen(msg)+1)sizeof(char)); strcpy(thread_arg, msg); pthread_t tid; pthread_create(&tid, NULL, thread, (void)thread_arg); void *rv; pthread_join(tid, &rv); } EOC test_thread("Just another XS hacker"); [download] Like you say, that crashes on Windows unless "free(msg;" is commented out. At least that's what I'm seeing on Strawberry-5.20.0. But it looks to me that the memory for "msg" has not been dynamically allocated, and therefore shouldn't be set free(). If you want to free() the memory what was malloc()'ed you can `free(thread_arg);` at the end of the test_thread() sub. However, I'm guessing that defeats the purpose of the demo. (Sorry - complete threads-idiot, here. Does the memory have to be free()'d in the thread sub ?) Cheers, Rob	[reply] [d/l] [select]
Re: XS: free() outside of the main thread causes crash on Windows by OlegG (Monk) on Sep 25, 2014 at 11:46 UTC
Just for the record. Here is how I finished with this problem: https://github.com/olegwtf/p5-Net-DNS-Native/blob/c8649041010076f57763e507ee7b9c71665afabe/Native.xs#L9 Line 9-15	[reply]
Re^2: XS: free() outside of the main thread causes crash on Windows by ikegami (Patriarch) on Sep 25, 2014 at 14:54 UTC
	[reply]
Re: XS: free() outside of the main thread causes crash on Windows by ikegami (Patriarch) on Sep 25, 2014 at 14:25 UTC
XS is Perl-aware glue, and as such, Perl redefines certain functions to Perl-aware functions. I'd start by separating your Perl-incompatible stuff (non-Perl threads, and the non-Perl memory allocation) from XS. A separate file would be good, but the following might suffice. `#include <pthread.h> void thread(void arg) { char msg = (char)arg; printf("thread: %s\n", msg); free(msg); return NULL; } void test_thread(const char msg) { char thread_arg = malloc((strlen(msg)+1)sizeof(char)); strcpy(thread_arg, msg); pthread_t tid; pthread_create(&tid, NULL, thread, (void)thread_arg); void rv; pthread_join(tid, &rv); } #include "EXTERN.h" #include "perl.h" #include "XSUB.h" #include "ppport.h" MODULE = My PACKAGE = My void test_thread(const char msg)` [download] Note that mid-block variable declarations (like `thread_arg`, `tid` and `rv` in your code, and the latter two in mine) aren't legal C89 which Perl supports. Of course, it doesn't mean you have to support it.	[reply] [d/l] [select]