[libc-commits] [PATCH] D98467: This introduces gmtime to LLVM libc, based on C99/C2X/Single Unix Spec.

[Siva Chandra via Phabricator via libc-commits]

sivachandra added inline comments.


================
Comment at: libc/src/time/gmtime.cpp:18
+LLVM_LIBC_FUNCTION(struct tm *, gmtime, (const time_t *timer)) {
+  // TODO(rtenneti): This method is not thread safe.
+  static struct tm tm_out;
----------------
jeffbailey wrote:
> sivachandra wrote:
> > Does any standard require thread safety? If yes, will making the below declaration thread-local solve the problem?
> C20 introduces gmtime_r (and the family of _r time functions).
> 
> In 7.27.3:
> 
> " Execution of any of the functions that return a pointer to one of these static
> objects may overwrite the information returned from any previous call to one of these functions that
> uses the same object. "
> 
> But what's not clear to me is for the non-reentrant versions, is doing a thread-local OK? I'm not seeing anything in the standard discussing static buffers and the use of thread-locals to store them (it only's mentioned in the definition of errno)
> 
Whether thread-local is OK or not depends on the supported uses cases. For example, if a change in value in one thread is to be visible from another thread, then making it a thread-local is not a good idea. If it is unclear from the standards, I would say just leave it as you have it here.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D98467/new/

https://reviews.llvm.org/D98467