GH-110829: Ensure Thread.join() joins the OS thread (#110848)

Joining a thread now ensures the underlying OS thread has exited. This is required for safer fork() in multi-threaded processes.

---------

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Python/thread_nt.h

@@ -182,9 +182,9 @@ bootstrap(void *call)
     return 0;
 }
 
-unsigned long
-PyThread_start_new_thread(void (*func)(void *), void *arg)
-{
+int
+PyThread_start_joinable_thread(void (*func)(void *), void *arg,
+                               PyThread_ident_t* ident, PyThread_handle_t* handle) {
     HANDLE hThread;
     unsigned threadID;
     callobj *obj;
@@ -194,7 +194,7 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
 
     obj = (callobj*)HeapAlloc(GetProcessHeap(), 0, sizeof(*obj));
     if (!obj)
-        return PYTHREAD_INVALID_THREAD_ID;
+        return -1;
     obj->func = func;
     obj->arg = arg;
     PyThreadState *tstate = _PyThreadState_GET();
@@ -207,22 +207,51 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
         /* I've seen errno == EAGAIN here, which means "there are
          * too many threads".
          */
-        int e = errno;
-        threadID = (unsigned)-1;
         HeapFree(GetProcessHeap(), 0, obj);
+        return -1;
     }
-    else {
-        CloseHandle(hThread);
+    *ident = threadID;
+    // The cast is safe since HANDLE is pointer-sized
+    *handle = (PyThread_handle_t) hThread;
+    return 0;
+}
+
+unsigned long
+PyThread_start_new_thread(void (*func)(void *), void *arg) {
+    PyThread_handle_t handle;
+    PyThread_ident_t ident;
+    if (PyThread_start_joinable_thread(func, arg, &ident, &handle)) {
+        return PYTHREAD_INVALID_THREAD_ID;
     }
-    return threadID;
+    CloseHandle((HANDLE) handle);
+    // The cast is safe since the ident is really an unsigned int
+    return (unsigned long) ident;
+}
+
+int
+PyThread_join_thread(PyThread_handle_t handle) {
+    HANDLE hThread = (HANDLE) handle;
+    int errored = (WaitForSingleObject(hThread, INFINITE) != WAIT_OBJECT_0);
+    CloseHandle(hThread);
+    return errored;
+}
+
+int
+PyThread_detach_thread(PyThread_handle_t handle) {
+    HANDLE hThread = (HANDLE) handle;
+    return (CloseHandle(hThread) == 0);
+}
+
+void
+PyThread_update_thread_after_fork(PyThread_ident_t* ident, PyThread_handle_t* handle) {
 }
 
 /*
  * Return the thread Id instead of a handle. The Id is said to uniquely identify the
  * thread in the system
  */
-unsigned long
-PyThread_get_thread_ident(void)
+PyThread_ident_t
+PyThread_get_thread_ident_ex(void)
 {
     if (!initialized)
         PyThread_init_thread();
@@ -230,6 +259,13 @@ PyThread_get_thread_ident(void)
     return GetCurrentThreadId();
 }
 
+unsigned long
+PyThread_get_thread_ident(void)
+{
+    return (unsigned long) PyThread_get_thread_ident_ex();
+}
+
+
 #ifdef PY_HAVE_THREAD_NATIVE_ID
 /*
  * Return the native Thread ID (TID) of the calling thread.

Python/thread_pthread.h

@@ -235,8 +235,8 @@ pythread_wrapper(void *arg)
     return NULL;
 }
 
-unsigned long
-PyThread_start_new_thread(void (*func)(void *), void *arg)
+static int
+do_start_joinable_thread(void (*func)(void *), void *arg, pthread_t* out_id)
 {
     pthread_t th;
     int status;
@@ -252,7 +252,7 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
 
 #if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
     if (pthread_attr_init(&attrs) != 0)
-        return PYTHREAD_INVALID_THREAD_ID;
+        return -1;
 #endif
 #if defined(THREAD_STACK_SIZE)
     PyThreadState *tstate = _PyThreadState_GET();
@@ -261,7 +261,7 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
     if (tss != 0) {
         if (pthread_attr_setstacksize(&attrs, tss) != 0) {
             pthread_attr_destroy(&attrs);
-            return PYTHREAD_INVALID_THREAD_ID;
+            return -1;
         }
     }
 #endif
@@ -272,7 +272,7 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
     pythread_callback *callback = PyMem_RawMalloc(sizeof(pythread_callback));
 
     if (callback == NULL) {
-      return PYTHREAD_INVALID_THREAD_ID;
+      return -1;
     }
 
     callback->func = func;
@@ -292,11 +292,34 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
 
     if (status != 0) {
         PyMem_RawFree(callback);
+        return -1;
+    }
+    *out_id = th;
+    return 0;
+}
+
+int
+PyThread_start_joinable_thread(void (*func)(void *), void *arg,
+                               PyThread_ident_t* ident, PyThread_handle_t* handle) {
+    pthread_t th = (pthread_t) 0;
+    if (do_start_joinable_thread(func, arg, &th)) {
+        return -1;
+    }
+    *ident = (PyThread_ident_t) th;
+    *handle = (PyThread_handle_t) th;
+    assert(th == (pthread_t) *ident);
+    assert(th == (pthread_t) *handle);
+    return 0;
+}
+
+unsigned long
+PyThread_start_new_thread(void (*func)(void *), void *arg)
+{
+    pthread_t th = (pthread_t) 0;
+    if (do_start_joinable_thread(func, arg, &th)) {
         return PYTHREAD_INVALID_THREAD_ID;
     }
-
     pthread_detach(th);
-
 #if SIZEOF_PTHREAD_T <= SIZEOF_LONG
     return (unsigned long) th;
 #else
@@ -304,20 +327,46 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
 #endif
 }
 
+int
+PyThread_join_thread(PyThread_handle_t th) {
+    return pthread_join((pthread_t) th, NULL);
+}
+
+int
+PyThread_detach_thread(PyThread_handle_t th) {
+    return pthread_detach((pthread_t) th);
+}
+
+void
+PyThread_update_thread_after_fork(PyThread_ident_t* ident, PyThread_handle_t* handle) {
+    // The thread id might have been updated in the forked child
+    pthread_t th = pthread_self();
+    *ident = (PyThread_ident_t) th;
+    *handle = (PyThread_handle_t) th;
+    assert(th == (pthread_t) *ident);
+    assert(th == (pthread_t) *handle);
+}
+
 /* XXX This implementation is considered (to quote Tim Peters) "inherently
    hosed" because:
      - It does not guarantee the promise that a non-zero integer is returned.
      - The cast to unsigned long is inherently unsafe.
      - It is not clear that the 'volatile' (for AIX?) are any longer necessary.
 */
-unsigned long
-PyThread_get_thread_ident(void)
-{
+PyThread_ident_t
+PyThread_get_thread_ident_ex(void) {
     volatile pthread_t threadid;
     if (!initialized)
         PyThread_init_thread();
     threadid = pthread_self();
-    return (unsigned long) threadid;
+    assert(threadid == (pthread_t) (PyThread_ident_t) threadid);
+    return (PyThread_ident_t) threadid;
+}
+
+unsigned long
+PyThread_get_thread_ident(void)
+{
+    return (unsigned long) PyThread_get_thread_ident_ex();
 }
 
 #ifdef PY_HAVE_THREAD_NATIVE_ID

Python/thread_pthread_stubs.h

@@ -94,6 +94,15 @@ pthread_detach(pthread_t thread)
     return 0;
 }
 
+int
+pthread_join(pthread_t thread, void** value_ptr)
+{
+    if (value_ptr) {
+        *value_ptr = NULL;
+    }
+    return 0;
+}
+
 PyAPI_FUNC(pthread_t) pthread_self(void)
 {
     return 0;