Move __cxa_thread_atexit to native code

Rather than using a separate JS array use pthread TLS key which get
cleaned during `__pthread_tsd_run_dtors`.

Followup to #14484 and #14464 which both move more of the cleanup
handling for threads and processes onto the native side.

Author: sbc100

src/library_pthread.js

@@ -52,7 +52,6 @@ var LibraryPThread = {
     },
     // Maps pthread_t to pthread info objects
     pthreads: {},
-    threadExitHandlers: [], // An array of C functions to run when this thread exits.
 
 #if PTHREADS_PROFILING
     createProfilerBlock: function(pthreadPtr) {
@@ -985,39 +984,12 @@ var LibraryPThread = {
     return 0;
   },
 
-  __pthread_exit_run_handlers__deps: ['exit'],
-  __pthread_exit_run_handlers: function(status) {
-    // Called from pthread_exit, either when called explicitly called
-    // by programmer, or implicitly when leaving the thread main function.
-    //
-    // Note: in theory we would like to return any offscreen canvases back to
-    // the main thread, but if we ever fetched a rendering context for them that
-    // would not be valid, so we don't try.
-
-#if PTHREADS_DEBUG
-    var tb = _pthread_self();
-    assert(tb);
-    err('Pthread 0x' + tb.toString(16) + ' exited.');
-#endif
-
-    while (PThread.threadExitHandlers.length > 0) {
-      PThread.threadExitHandlers.pop()();
-    }
-  },
-
   __pthread_detached_exit: function() {
     // Called at the end of pthread_exit (which occurs also when leaving the
     // thread main function) if an only if the thread is in a detached state.
     postMessage({ 'cmd': 'detachedExit' });
   },
 
-  __cxa_thread_atexit__sig: 'vii',
-  __cxa_thread_atexit: function(routine, arg) {
-    PThread.threadExitHandlers.push(function() { {{{ makeDynCall('vi', 'routine') }}}(arg) });
-  },
-  __cxa_thread_atexit_impl: '__cxa_thread_atexit',
-
-
   // Returns 0 on success, or one of the values -ETIMEDOUT, -EWOULDBLOCK or -EINVAL on error.
   emscripten_futex_wait__deps: ['emscripten_main_thread_process_queued_calls'],
   emscripten_futex_wait: function(addr, val, timeout) {

system/lib/libcxxabi/src/cxa_thread_atexit.cpp

@@ -112,9 +112,14 @@ extern "C" {
 #ifdef HAVE___CXA_THREAD_ATEXIT_IMPL
     return __cxa_thread_atexit_impl(dtor, obj, dso_symbol);
 #else
+#ifndef __EMSCRIPTEN__
+    // Emscripten doesn't supported fully support weak undefined symbols yet
+    // https://github.com/emscripten-core/emscripten/issues/12819
     if (__cxa_thread_atexit_impl) {
       return __cxa_thread_atexit_impl(dtor, obj, dso_symbol);
-    } else {
+    } else
+#endif
+    {
       // Initialize the dtors std::__libcpp_tls_key (uses __cxa_guard_*() for
       // one-time initialization and __cxa_atexit() for destruction)
       static DtorsManager manager;

system/lib/pthread/library_pthread.c

@@ -6,8 +6,7 @@
  */
 
 #define _GNU_SOURCE
-#include "../internal/libc.h"
-#include "../internal/pthread_impl.h"
+
 #include <assert.h>
 #include <dirent.h>
 #include <errno.h>
@@ -34,6 +33,9 @@
 #include <emscripten.h>
 #include <emscripten/threading.h>
 
+#include "libc.h"
+#include "pthread_impl.h"
+
 // Extra pthread_attr_t field:
 #define _a_transferredcanvases __u.__s[9]
 

system/lib/pthread/pthread_create.c

@@ -22,7 +22,6 @@
 extern int __cxa_thread_atexit(void (*)(void *), void *, void *);
 extern int __pthread_create_js(struct pthread *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg);
 extern void _emscripten_thread_init(int, int, int);
-extern void __pthread_exit_run_handlers();
 extern void __pthread_detached_exit();
 extern void* _emscripten_tls_base();
 extern int8_t __dso_handle;
@@ -126,10 +125,6 @@ void _emscripten_thread_exit(void* result) {
   // Run any handlers registered with pthread_cleanup_push
   __run_cleanup_handlers();
 
-  // Run any JS thread exit handlers (for C++ programs this includes any
-  // functions registered with __cxa_thread_atexit).
-  __pthread_exit_run_handlers();
-
   // Call into the musl function that runs destructors of all thread-specific data.
   __pthread_tsd_run_dtors();
 

tools/system_libs.py

@@ -986,6 +986,7 @@ def get_files(self):
       'cxa_guard.cpp',
       'cxa_handlers.cpp',
       'cxa_virtual.cpp',
+      'cxa_thread_atexit.cpp',
       'fallback_malloc.cpp',
       'stdlib_new_delete.cpp',
       'stdlib_exception.cpp',