Fix signals delivery fail in find-leak mode if init from non-main thread

Issue #542 (bdwgc).

The scenario of the failure (on Linux):
- Find-leak mode is on
- pthread_create/join primitives are not redirected
- GC is initialized from a thread other than primordial
- that thread is terminated (but not unregistered as the 1st one in GC)
- the primordial thread exits and launches GC_exit_check
- GC_gcollect tries to suspend the terminated thread by sending a signal
- the signal is not delivered but pthread_kill just returns zero
- the signal sending is retried until aborting with the proper message.

The proposed solution (workaround) is not to call GC_gcollect at
the process exit (in the find-leak mode) if GC_init was called from
a thread other than primordial one.

Check in GC_exit_check() (which is called if GC_find_leak) that the
thread executing at-exit functions is the same as the one performed
the GC initialization, otherwise the latter thread might already be
dead but still registered and this, as a consequence, might cause
a signal delivery fail when suspending the threads on platforms that
do not guarantee ESRCH returned if the signal is not delivered (as
observed on Ubuntu 22).

* include/private/gc_priv.h [THREADS && !DONT_USE_ATEXIT]
(GC_is_main_thread): Declare GC_INNER function.
* include/private/pthread_support.h [GC_WIN32_THREADS
&& !DONT_USE_ATEXIT] (GC_main_thread_id): Declare variable.
* include/private/pthread_support.h [GC_WIN32_THREADS
&& !GC_NO_THREADS_DISCOVERY] (GC_main_thread_id): Do not depend on
GC_ASSERTIONS.
* misc.c [!DONT_USE_ATEXIT && THREADS] (GC_exit_check): If not
GC_is_main_thread() or not GC_thread_is_registered() then do not call
GC_gcollect(); add comment; do not set and clear GC_in_thread_creation.
* pthread_support.c [!GC_NO_THREADS_DISCOVERY && GC_WIN32_THREADS
|| !DONT_USE_ATEXIT] (GC_main_thread_id): Define variable.
* pthread_support.c [!DONT_USE_ATEXIT] (GC_is_main_thread): Implement.
* pthread_support.c [!GC_WIN32_THREADS] (GC_thr_init): Define self_id
local variable.
* pthread_support.c [!GC_WIN32_THREADS && !DONT_USE_ATEXIT]
(GC_thr_init): Set GC_main_thread_id.
* win32_threads.c [!DONT_USE_ATEXIT] (GC_thr_init): Likewise.
* win32_threads.c [!GC_NO_THREADS_DISCOVERY] (GC_main_thread_id): Do
not define variable.

1 files changed, 18 insertions, 1 deletions

diff --git a/pthread_support.c b/pthread_support.c
index 7e42b1bc..30addcbe 100644
--- a/pthread_support.c
+++ b/pthread_support.c
@@ -1489,6 +1489,19 @@ GC_INNER_WIN32THREAD void GC_record_stack_base(GC_stack_context_t crtn,
 # endif
 }
 
+#if !defined(GC_NO_THREADS_DISCOVERY) && defined(GC_WIN32_THREADS) \
+    || !defined(DONT_USE_ATEXIT)
+  GC_INNER_WIN32THREAD thread_id_t GC_main_thread_id;
+#endif
+
+#ifndef DONT_USE_ATEXIT
+  GC_INNER GC_bool GC_is_main_thread(void)
+  {
+    GC_ASSERT(GC_thr_initialized);
+    return thread_id_self() == GC_main_thread_id;
+  }
+#endif /* !DONT_USE_ATEXIT */
+
 #ifndef GC_WIN32_THREADS
 
 STATIC GC_thread GC_register_my_thread_inner(const struct GC_stack_base *sb,
@@ -1645,6 +1658,7 @@ GC_INNER void GC_thr_init(void)
     struct GC_stack_base sb;
     GC_thread me;
     GC_stack_context_t crtn;
+    thread_id_t self_id = thread_id_self();
 
     sb.mem_base = GC_stackbottom;
     GC_ASSERT(sb.mem_base != NULL);
@@ -1654,7 +1668,10 @@ GC_INNER void GC_thr_init(void)
       sb.reg_base = NULL;
 #   endif
     GC_ASSERT(NULL == GC_self_thread_inner());
-    me = GC_register_my_thread_inner(&sb, thread_id_self());
+    me = GC_register_my_thread_inner(&sb, self_id);
+#   ifndef DONT_USE_ATEXIT
+      GC_main_thread_id = self_id;
+#   endif
     me -> flags = DETACHED;
     /* Copy the alt-stack information if set. */
     crtn = me -> crtn;