[pthread] pthread+printf may have bugs

[pthread] pthread+printf may have bugs

[陈晓晖]

Hi,

    I found that pthread may stop work if using printf in thread.
I'm not sure that printf is thread safe or not, so I tried to wrap the
printf with a mutex, but the problem still exists.
After I removed all printfs, everything is OK.

The testing environment:
$ uname -a
CYGWIN_NT-5.1 compname 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwin
Windows XP SP3 ( ver 2600 )

The testing code:


#include <pthread.h>
#include <stdio.h>
#include <semaphore.h>
#include <stdlib.h>
#include <stdarg.h>


pthread_mutex_t m;

void my_printf( const char *fmt, ... )
{
    va_list va;
    va_start( va, fmt );
    pthread_mutex_lock( &m );
    vprintf( fmt, va );
    pthread_mutex_unlock( &m );
    va_end( va );
}

void *thread_entry( void *data )
{
    my_printf( "in thread_entry %d\n", __LINE__ );
    my_printf( "in thread_entry %d\n", __LINE__ );
    my_printf( "in thread_entry %d\n", __LINE__ );
    return NULL;
}

void create_thread( pthread_t *thread_id )
{
    my_printf( "before thread create\n" );

    if ( pthread_create(
        thread_id,
        NULL,
        &thread_entry,
        NULL
        ) != 0 )
    {
        my_printf( "error" );
        exit( 0 );
    }

    my_printf( "after thread create\n" );
    my_printf( "before create_thread return\n" );
}



int main( )
{
#define N 30

    int i;
    pthread_t threads[N];

    pthread_mutex_init( &m, NULL );
    printf( "create threads\n" );
    for( i = 0; i < N; ++i )
        create_thread( &threads[i] );

    printf( "wait threads\n" );
    for( i = 0; i < N; ++i )
        pthread_join( threads[i], NULL );

    pthread_mutex_destroy( &m );
    printf( "exit...\n" );
    return 0;
}

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Re: [pthread] pthread+printf may have bugs

[陈晓晖]

It is strange that the error disappeared if replacing any cygwin1.dll
on the snapshot page
    http://cygwin.com/snapshots/
For these versions, I see a more line "Huh?  No /etc/fstab file?
Using default root and cygdrive prefix..." was printed.

By the way, does anybody know where can I find the pthread source for
cygwin? is it pthread-win32? Thanks ..
I want to look into it.


2008/12/24 陈晓晖 <xhchen8018@gmail.com>:
> Hi,
>
>    I found that pthread may stop work if using printf in thread.
> I'm not sure that printf is thread safe or not, so I tried to wrap the
> printf with a mutex, but the problem still exists.
> After I removed all printfs, everything is OK.
>

Re: [pthread] pthread+printf may have bugs

[Christopher Faylor]

On Thu, Dec 25, 2008 at 10:52:14AM +0800, "?????????" wrote:
>It is strange that the error disappeared if replacing any cygwin1.dll
>on the snapshot page
>    http://cygwin.com/snapshots/
>For these versions, I see a more line "Huh?  No /etc/fstab file?  Using
>default root and cygdrive prefix..." was printed.

The snapshots are based on version 1.7 of the Cygwin DLL:

http://cygwin.com/ml/cygwin-announce/2008-12/msg00028.html

This version has a few pthreads fixes.

>By the way, does anybody know where can I find the pthread source for
>cygwin? is it pthread-win32? Thanks ..
>I want to look into it.

The source code for the snapshots is available at the same place where
you downloaded the snapshot.  The source code for Cygwin 1.5.25 is
available for download via setup.exe.

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