* cygthread.cc (cygthread::stub): Detect if thread function wants to release

itself here, to avoid a race.
(cygthread::release): Clear more stuff.  Add a diagnostic for an internal
error.
* cygthread.h (auto_release): New function.
* pinfo.h (pinfo::remember): Add an argument to denote whether child is
detached.
* fork.cc (fork_parent): Reflect change in arguments to pinfo::remember.
* pinfo.cc (_pinfo::exit): Signal exit more forcibly.
(proc_waiter): Use cygthread::auto_release to signify that cygthread::stub
should release the thread.  This should avoid a race.
(pinfo::alert_parent): Don't signify an error when wr_proc_pipe == NULL.
* sigproc.cc (proc_subproc): Add support for PROC_DETACHED_CHILD.
* sigproc.h: Ditto.
* spawn.cc (spawn_guts): Specify whether child is detached or not when calling
pinfo::remember.

winsup/cygwin/fork.cc

@@ -413,7 +413,7 @@ fork_parent (HANDLE& hParent, dll *&first_dll,
      it in afterwards.  This requires more bookkeeping than I like, though,
      so we'll just do it the easy way.  So, terminate any child process if
      we can't actually record the pid in the internal table. */
-  if (!child.remember ())
+  if (!child.remember (false))
     {
       TerminateProcess (pi.hProcess, 1);
       set_errno (EAGAIN);