[PATCH]: Thread safe stdio with cygwin

Jeff Johnston jjohnstn@redhat.com
Thu Jan 15 16:38:00 GMT 2004

Thomas Pfaff wrote:

> Jeff,
> memset makes only sure that _lock does not contain random data before 
> __lock_init_recursive. __lock_init_recursive is called later when the 
> file is really opened.

I assumed you were worried about something accessing the file pointer 
before fopen/freopen returned the file pointer so it would then make 
sense just to initialize it earlier.  Otherwise, the 
__lock_init_recursive should initialize the lock without need for 

> __sbprintf is a special case because it generates a fake FILE pointer 
> and its associated buf on the stack, therefore there is no need to 
> lock it fo thread safety.

There may be no need to lock, but the VFPRINTF code attempts a lock and 
unlock anyway.  It then makes sense to ensure that the lock is validly 
initialized/closed for any platform's lock implementation. 

-- Jeff J.

> Thomas
> Jeff Johnston wrote:
>> Thomas,
>>  You should be using __lock_init_recursive to initialize the locks 
>> rather than zeroing them out.
>> The code in __sbprintf should probably be closing the lock after the 
>> call to VFPRINTF as well.
>> -- Jeff J.
>> Thomas Pfaff wrote:
>>> This patch adds support for thread safe stdio for Cygwin.
>>> Cygwin uses dynamic mutexes for locking, therefore it is
>>> necessary to:
>>> 1. Initialize FILE pointers _lock properly.
>>> 2. Destroy the lock when it is no longer needed.
>>> Regards,
>>> Thomas
>>> 2004-01-12  Thomas Pfaff  <tpfaff@gmx.net>
>>>     * libc/stdio/fclose.c: Include sys/lock.h.
>>>     (fclose): Destroy lock when file is closed.
>>>     * libc/stdio/findfp.c (__sfp): Initialize file pointers _lock
>>>     member.
>>>     * libc/stdio/freopen.c: Include sys/lock.h.
>>>     (_freopen_r): Destroy lock when file is closed.
>>>     * libc/stdio/vfprintf.c (__sbprintf): Initialize file pointers
>>>     _lock member.

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