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Issues with struct timespec
- From: Mark Pizzolato - pthreads - win32 <MarkPizzolato-pthreads-win32 at subscriptions dot pizzolato dot net>
- To: "pthreads-win32 at sourceware dot org" <pthreads-win32 at sourceware dot org>
- Date: Thu, 12 Jan 2012 13:06:31 -0800
- Subject: Issues with struct timespec
In the older versions of pthreads-win32 struct timespec had a tv_sec member which was of type long.
In the current CVS code base this member has been changed to be of type time_t.
The only reason struct timespec exists in pthreads-win32 is to support pthread_cond_timedwait(). Pthread.h is providing a definition for struct timespec since, in general there is no other use of that structure in a win32 programming environment. It is unique to pthreads.
A problem exists for an application which may use the provided struct timespec definition with pthread_cond_timedwait(). If that application is linking against a prebuilt version of the pthreads code (the most common case), the pthreads library will have been built with a time_t type which is whatever the current compiler/build default size for that type (64bits these days, but 32bits in the past). Meanwhile, the application using pthreads can have a time_t type which could be 32 or 64 bits completely depending on compile time defines. Calls to pthread_cond_timedwait() will be passing a struct timespec which may or may not have a time_t element size consistent with the time_t in use when the pthread library was built.
I would suggest that struct timespec should use a non variable sized type for the tv_sec member. A type of long should be just fine for normal uses of pthread_cond_timedwait() for most of the next 36 years. A 64bit type could just as well be used if all of the pthread-win32 target platforms support 64bit numbers, or it could be a fixed size but be specific to the platform as needed.
While we're here, anyone who uses a struct timespec passed to pthread_cond_timedwait() actually needs to construct the contents of that structure in some way. We may want to provide a clock_gettime() implementation as part of pthreads-win32 to make the use of this API a little more natural and/or portable.
I'll be glad to suggest specific code for these ideas depending on what others think of the issue.
Looking forward to a discussion.
- Mark Pizzolato