K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2020-02-13T23:22:12.397837Z
K 7
svn:log
V 958
Return success, instead of ESRCH, from pthread_cancel(3) applied to the
exited but not yet joined thread.

Before, if the thread exited but was not yet joined, we returned
ESRCH.

According to IEEE Std 1003.1™-2017 recommendation in the
description of pthread_cancel(3):
  If an implementation detects use of a thread ID after the end of its
  lifetime, it is recommended that the function should fail and report
  an [ESRCH] error.
So it seems desirable to not return ESRCH until the lifetime of the
thread ID ends.  According to the section 2.9.2 Thread IDs,
  The lifetime of a thread ID ends after the thread terminates if it
  was created with the detachstate attribute set to
  PTHREAD_CREATE_DETACHED or if pthread_detach() or pthread_join()
  has been called for that thread.
In other words, lifetime for thread ID of exited but not yet joined thread
did not ended yet.

Prompted by:	cperciva
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

END