Fix error reporting from pthread_join (#15417)

pthread_join should check for thread validity and for detached state
before it checks for joining self (i.e. deadlock).

Needed for (split out from) #13006.

Author: sbc100

src/library_pthread.js

@@ -878,25 +878,24 @@ var LibraryPThread = {
       err('pthread_join attempted on a null thread pointer!');
       return {{{ cDefine('ESRCH') }}};
     }
-    if (ENVIRONMENT_IS_PTHREAD && _pthread_self() == thread) {
-      err('PThread ' + thread + ' is attempting to join to itself!');
-      return {{{ cDefine('EDEADLK') }}};
-    }
-    else if (!ENVIRONMENT_IS_PTHREAD && _emscripten_main_browser_thread_id() == thread) {
-      err('Main thread ' + thread + ' is attempting to join to itself!');
-      return {{{ cDefine('EDEADLK') }}};
-    }
     var self = {{{ makeGetValue('thread', C_STRUCTS.pthread.self, 'i32') }}};
     if (self !== thread) {
       err('pthread_join attempted on thread ' + thread + ', which does not point to a valid thread, or does not exist anymore!');
       return {{{ cDefine('ESRCH') }}};
     }
-
     var detached = Atomics.load(HEAPU32, (thread + {{{ C_STRUCTS.pthread.detached }}} ) >> 2);
     if (detached) {
       err('Attempted to join thread ' + thread + ', which was already detached!');
       return {{{ cDefine('EINVAL') }}}; // The thread is already detached, can no longer join it!
     }
+    if (ENVIRONMENT_IS_PTHREAD && _pthread_self() == thread) {
+      err('PThread ' + thread + ' is attempting to join to itself!');
+      return {{{ cDefine('EDEADLK') }}};
+    }
+    else if (!ENVIRONMENT_IS_PTHREAD && _emscripten_main_browser_thread_id() == thread) {
+      err('Main thread ' + thread + ' is attempting to join to itself!');
+      return {{{ cDefine('EDEADLK') }}};
+    }
 
 #if ASSERTIONS || IN_TEST_HARNESS || !MINIMAL_RUNTIME || !ALLOW_BLOCKING_ON_MAIN_THREAD
     if (block) {

tests/other/test_pthread_self_join_detach.c

@@ -2,21 +2,41 @@
 #include <errno.h>
 #include <pthread.h>
 #include <stdio.h>
+#include <string.h>
 
 #include <emscripten/threading.h>
 
 int main() {
+  /*
+   * When running in PROXY_TO_PTHREAD mode the main thread
+   * is already detached
+   */
+  int is_detached = !emscripten_is_main_browser_thread();
   pthread_t self = pthread_self();
 
-  /* Join the calling thread. This should fail with EDEADLK. */
-  assert(pthread_join(self, NULL) == EDEADLK);
+  /*
+   * Attempts to join the current thread will either generate
+   * EDEADLK or EINVAL depending on whether has already been
+   * detached
+   */
+  int ret = pthread_join(self, NULL);
+  if (is_detached) {
+    assert(ret == EINVAL);
+  } else {
+    assert(ret == EDEADLK);
+  }
 
-  /* We should be able to detach the main thread,
-   * but not the proxied main thread (as that one
-   * is already detached).
+  /*
+   * Attempts to detach the main thread will either succeed
+   * or cause EINVAL if its already been detached.
    */
-  int ret = emscripten_is_main_browser_thread() ? 0 : EINVAL;
-  assert(pthread_detach(self) == ret);
+  ret = pthread_detach(self);
+  printf("pthread_detach(self) -> %s\n", strerror(ret));
+  if (is_detached) {
+    assert(ret == EINVAL);
+  } else {
+    assert(ret == 0);
+  }
 
   puts("passed");