Move pthread_cancel to native code. NFC. (#15603)

Author: kleisauke

src/library_pthread.js

@@ -408,6 +408,11 @@ var LibraryPThread = {
   },
 
   __emscripten_thread_cleanup: function(thread) {
+    // Called when a thread needs to be cleaned up so it can be reused.
+    // A thread is considered reusable when it either returns from its
+    // entry point, calls pthread_exit, or acts upon a cancellation.
+    // Detached threads are responsible for calling this themselves,
+    // otherwise pthread_join is responsible for calling this.
     if (!ENVIRONMENT_IS_PTHREAD) cleanupThread(thread);
     else postMessage({ 'cmd': 'cleanupThread', 'thread': thread });
   },
@@ -751,12 +756,12 @@ var LibraryPThread = {
 #endif
   },
 
-  pthread_kill__deps: ['$killThread', 'emscripten_main_browser_thread_id'],
+  pthread_kill__deps: ['emscripten_main_browser_thread_id'],
   pthread_kill: function(thread, signal) {
     if (signal < 0 || signal >= 65/*_NSIG*/) return {{{ cDefine('EINVAL') }}};
     if (thread === _emscripten_main_browser_thread_id()) {
       if (signal == 0) return 0; // signal == 0 is a no-op.
-      err('Main thread (id=' + thread + ') cannot be killed with pthread_kill!');
+      err('Main thread (id=0x' + thread.toString(16) + ') cannot be killed with pthread_kill!');
       return {{{ cDefine('ESRCH') }}};
     }
     if (!thread) {
@@ -765,38 +770,19 @@ var LibraryPThread = {
     }
     var self = {{{ makeGetValue('thread', C_STRUCTS.pthread.self, 'i32') }}};
     if (self !== thread) {
-      err('pthread_kill attempted on thread ' + thread + ', which does not point to a valid thread, or does not exist anymore!');
+      err('pthread_kill attempted on thread 0x' + thread.toString(16) + ', which does not point to a valid thread, or does not exist anymore!');
       return {{{ cDefine('ESRCH') }}};
     }
-    if (signal != 0) {
+    if (signal === {{{ cDefine('SIGCANCEL') }}}) { // Used by pthread_cancel in musl
+      if (!ENVIRONMENT_IS_PTHREAD) cancelThread(thread);
+      else postMessage({ 'cmd': 'cancelThread', 'thread': thread });
+    } else if (signal != 0) {
       if (!ENVIRONMENT_IS_PTHREAD) killThread(thread);
-      else postMessage({ 'cmd': 'killThread', 'thread': thread});
+      else postMessage({ 'cmd': 'killThread', 'thread': thread });
     }
     return 0;
   },
 
-  pthread_cancel__deps: ['$cancelThread', 'emscripten_main_browser_thread_id'],
-  pthread_cancel: function(thread) {
-    if (thread === _emscripten_main_browser_thread_id()) {
-      err('Main thread (id=' + thread + ') cannot be canceled!');
-      return {{{ cDefine('ESRCH') }}};
-    }
-    if (!thread) {
-      err('pthread_cancel attempted on a null thread pointer!');
-      return {{{ cDefine('ESRCH') }}};
-    }
-    var self = {{{ makeGetValue('thread', C_STRUCTS.pthread.self, 'i32') }}};
-    if (self !== thread) {
-      err('pthread_cancel attempted on thread ' + thread + ', which does not point to a valid thread, or does not exist anymore!');
-      return {{{ cDefine('ESRCH') }}};
-    }
-    // Signal the thread that it needs to cancel itself.
-    Atomics.store(HEAPU32, (thread + {{{ C_STRUCTS.pthread.cancel }}}) >> 2, 1);
-    if (!ENVIRONMENT_IS_PTHREAD) cancelThread(thread);
-    else postMessage({ 'cmd': 'cancelThread', 'thread': thread});
-    return 0;
-  },
-
   // Returns 0 on success, or one of the values -ETIMEDOUT, -EWOULDBLOCK or -EINVAL on error.
   _emscripten_futex_wait_non_blocking__deps: ['emscripten_main_thread_process_queued_calls'],
   _emscripten_futex_wait_non_blocking: function(addr, val, timeout) {

src/struct_info_internal.json

@@ -29,7 +29,10 @@
                 "timeSpentInStatus",
                 "name"
             ]
-        }
+        },
+        "defines": [
+          "SIGCANCEL"
+        ]
     },
     {
         "file": "dynlink.h",

system/lib/libc/musl/src/thread/pthread_cancel.c

@@ -3,6 +3,7 @@
 #include "pthread_impl.h"
 #include "syscall.h"
 
+#ifndef __EMSCRIPTEN__
 hidden long __cancel(), __syscall_cp_asm(), __syscall_cp_c();
 
 long __cancel()
@@ -83,14 +84,17 @@ static void init_cancellation()
 	memset(&sa.sa_mask, -1, _NSIG/8);
 	__libc_sigaction(SIGCANCEL, &sa, 0);
 }
+#endif
 
 int pthread_cancel(pthread_t t)
 {
+#ifndef __EMSCRIPTEN__
 	static int init;
 	if (!init) {
 		init_cancellation();
 		init = 1;
 	}
+#endif
 	a_store(&t->cancel, 1);
 	if (t == pthread_self()) {
 		if (t->canceldisable == PTHREAD_CANCEL_ENABLE && t->cancelasync)

tests/reference_struct_info.json

@@ -322,6 +322,7 @@
         "SEEK_END": 2,
         "SEEK_SET": 0,
         "SIGALRM": 14,
+        "SIGCANCEL": 33,
         "SOCK_CLOEXEC": 524288,
         "SOCK_DGRAM": 2,
         "SOCK_NONBLOCK": 2048,

tools/system_libs.py

@@ -823,7 +823,6 @@ def get_files(self):
         # TODO: Support this. See #12216.
         'pthread_setname_np.c',
         # TODO: These could be moved away from JS in the upcoming musl upgrade.
-        'pthread_cancel.c',
         'pthread_join.c', 'pthread_testcancel.c',
       ]
       libc_files += files_in_path(