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Date: Sun, 28 Sep 2008 17:49:30 +0200
From: =?UTF-8?B?VsOhY2xhdiBIYWlzbWFu?= <v DOT haisman AT sh DOT cvut DOT cz>
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To: cygwin AT cygwin DOT com
Subject: Re: crash if fork(2) from another thread
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Christopher Faylor wrote, On 28.9.2008 17:25:
> On Sun, Sep 28, 2008 at 09:32:39AM +0200, V??clav Haisman wrote:
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>> Hirokazu Yamamoto wrote, On 28.9.2008 4:16:
>>> # I've post mail, but it didn't show up in
>>> http://www.nabble.com/Cygwin-f12165.html.
>>> # Maybe it was not good to attach a file. So try again...
>>>
>>> I'm not familiar with pthread & fork, but I think following code should not
>>> crash. Is this expected behavior?
>>>
>>> #include <stdio.h>
>>> #include <stdlib.h>
>>> #include <pthread.h>
>>> #include <assert.h>
>>>
>>> void *thread_func(void* args)
>>> {
>>>     int ret;
>>>     pid_t pid;
>>>     pthread_t thread;
>>>
>>>     puts("thread_func");
>>>
>>>     pid = fork();
>>>
>>>     assert(pid != (pid_t)-1);
>>>
>>>     if (pid != 0) /* parent process */
>>>     {
>>>         int status;
>>>
>>>         printf("parent process (child pid = %d)\n", pid);
>>>
>>>         waitpid(pid, &status, 0);
>>>
>>>         puts("parent process end");
>>>     }
>>>     else /* child process */
>>>     {
>>>         puts("child process"); /* crash here */
>> I think this is not allowed in here.  You can only do async-signal-safe
>> stuff in the child.  IO is AFAIK not in that category.  Basically, the
>> only thing you can safely do in the child process is to call exec().
> 
> I don't see any reason why this shouldn't be allowed.  You should
> be able to do anything you want in a child process.
I do not think that is true. As per
<http://www.opengroup.org/onlinepubs/009695399/functions/fork.html>,
RATIONALE, the penultimate paragraph, it is basically undefined behaviour.


- --
VH
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