gh-134745: Change PyThread_allocate_lock() implementation to PyMutex (#134747)

Co-authored-by: Sam Gross <colesbury@gmail.com>

Author: vstinner

Include/internal/pycore_lock.h

@@ -48,6 +48,9 @@ typedef enum _PyLockFlags {
 
     // Handle signals if interrupted while waiting on the lock.
     _PY_LOCK_HANDLE_SIGNALS = 2,
+
+    // Fail if interrupted by a signal while waiting on the lock.
+    _PY_FAIL_IF_INTERRUPTED = 4,
 } _PyLockFlags;
 
 // Lock a mutex with an optional timeout and additional options. See

Lib/test/test_sys.py

@@ -729,7 +729,7 @@ def test_thread_info(self):
         info = sys.thread_info
         self.assertEqual(len(info), 3)
         self.assertIn(info.name, ('nt', 'pthread', 'pthread-stubs', 'solaris', None))
-        self.assertIn(info.lock, ('semaphore', 'mutex+cond', None))
+        self.assertIn(info.lock, ('pymutex', None))
         if sys.platform.startswith(("linux", "android", "freebsd")):
             self.assertEqual(info.name, "pthread")
         elif sys.platform == "win32":

Misc/NEWS.d/next/C_API/2025-05-30-11-33-17.gh-issue-134745.GN-zk2.rst

@@ -0,0 +1,3 @@
+Change :c:func:`!PyThread_allocate_lock` implementation to ``PyMutex``.
+On Windows, :c:func:`!PyThread_acquire_lock_timed` now supports the *intr_flag*
+parameter: it can be interrupted. Patch by Victor Stinner.

Python/lock.c

@@ -119,6 +119,9 @@ _PyMutex_LockTimed(PyMutex *m, PyTime_t timeout, _PyLockFlags flags)
                 return PY_LOCK_INTR;
             }
         }
+        else if (ret == Py_PARK_INTR && (flags & _PY_FAIL_IF_INTERRUPTED)) {
+            return PY_LOCK_INTR;
+        }
         else if (ret == Py_PARK_TIMEOUT) {
             assert(timeout >= 0);
             return PY_LOCK_FAILURE;

Python/thread.c

@@ -39,7 +39,8 @@
 const long long PY_TIMEOUT_MAX = PY_TIMEOUT_MAX_VALUE;
 
 
-static void PyThread__init_thread(void); /* Forward */
+/* Forward declaration */
+static void PyThread__init_thread(void);
 
 #define initialized _PyRuntime.threads.initialized
 
@@ -71,6 +72,79 @@ PyThread_init_thread(void)
 #endif
 
 
+/*
+ * Lock support.
+ */
+
+PyThread_type_lock
+PyThread_allocate_lock(void)
+{
+    if (!initialized) {
+        PyThread_init_thread();
+    }
+
+    PyMutex *lock = (PyMutex *)PyMem_RawMalloc(sizeof(PyMutex));
+    if (lock) {
+        *lock = (PyMutex){0};
+    }
+
+    return (PyThread_type_lock)lock;
+}
+
+void
+PyThread_free_lock(PyThread_type_lock lock)
+{
+    PyMem_RawFree(lock);
+}
+
+PyLockStatus
+PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
+                            int intr_flag)
+{
+    PyTime_t timeout;  // relative timeout
+    if (microseconds >= 0) {
+        // bpo-41710: PyThread_acquire_lock_timed() cannot report timeout
+        // overflow to the caller, so clamp the timeout to
+        // [PyTime_MIN, PyTime_MAX].
+        //
+        // PyTime_MAX nanoseconds is around 292.3 years.
+        //
+        // _thread.Lock.acquire() and _thread.RLock.acquire() raise an
+        // OverflowError if microseconds is greater than PY_TIMEOUT_MAX.
+        timeout = _PyTime_FromMicrosecondsClamp(microseconds);
+    }
+    else {
+        timeout = -1;
+    }
+
+    _PyLockFlags flags = _Py_LOCK_DONT_DETACH;
+    if (intr_flag) {
+        flags |= _PY_FAIL_IF_INTERRUPTED;
+    }
+
+    return _PyMutex_LockTimed((PyMutex *)lock, timeout, flags);
+}
+
+void
+PyThread_release_lock(PyThread_type_lock lock)
+{
+    PyMutex_Unlock((PyMutex *)lock);
+}
+
+int
+_PyThread_at_fork_reinit(PyThread_type_lock *lock)
+{
+    _PyMutex_at_fork_reinit((PyMutex *)lock);
+    return 0;
+}
+
+int
+PyThread_acquire_lock(PyThread_type_lock lock, int waitflag)
+{
+    return PyThread_acquire_lock_timed(lock, waitflag ? -1 : 0, /*intr_flag=*/0);
+}
+
+
 /* return the current thread stack size */
 size_t
 PyThread_get_stacksize(void)
@@ -261,11 +335,7 @@ PyThread_GetInfo(void)
 #ifdef HAVE_PTHREAD_STUBS
     value = Py_NewRef(Py_None);
 #elif defined(_POSIX_THREADS)
-#ifdef USE_SEMAPHORES
-    value = PyUnicode_FromString("semaphore");
-#else
-    value = PyUnicode_FromString("mutex+cond");
-#endif
+    value = PyUnicode_FromString("pymutex");
     if (value == NULL) {
         Py_DECREF(threadinfo);
         return NULL;

Python/thread_nt.h

@@ -300,98 +300,6 @@ PyThread_hang_thread(void)
     }
 }
 
-/*
- * Lock support. It has to be implemented as semaphores.
- * I [Dag] tried to implement it with mutex but I could find a way to
- * tell whether a thread already own the lock or not.
- */
-PyThread_type_lock
-PyThread_allocate_lock(void)
-{
-    PNRMUTEX mutex;
-
-    if (!initialized)
-        PyThread_init_thread();
-
-    mutex = AllocNonRecursiveMutex() ;
-
-    PyThread_type_lock aLock = (PyThread_type_lock) mutex;
-    assert(aLock);
-
-    return aLock;
-}
-
-void
-PyThread_free_lock(PyThread_type_lock aLock)
-{
-    FreeNonRecursiveMutex(aLock) ;
-}
-
-// WaitForSingleObject() accepts timeout in milliseconds in the range
-// [0; 0xFFFFFFFE] (DWORD type). INFINITE value (0xFFFFFFFF) means no
-// timeout. 0xFFFFFFFE milliseconds is around 49.7 days.
-const DWORD TIMEOUT_MS_MAX = 0xFFFFFFFE;
-
-/*
- * Return 1 on success if the lock was acquired
- *
- * and 0 if the lock was not acquired. This means a 0 is returned
- * if the lock has already been acquired by this thread!
- */
-PyLockStatus
-PyThread_acquire_lock_timed(PyThread_type_lock aLock,
-                            PY_TIMEOUT_T microseconds, int intr_flag)
-{
-    assert(aLock);
-
-    /* Fow now, intr_flag does nothing on Windows, and lock acquires are
-     * uninterruptible.  */
-    PyLockStatus success;
-    PY_TIMEOUT_T milliseconds;
-
-    if (microseconds >= 0) {
-        milliseconds = microseconds / 1000;
-        // Round milliseconds away from zero
-        if (microseconds % 1000 > 0) {
-            milliseconds++;
-        }
-        if (milliseconds > (PY_TIMEOUT_T)TIMEOUT_MS_MAX) {
-            // bpo-41710: PyThread_acquire_lock_timed() cannot report timeout
-            // overflow to the caller, so clamp the timeout to
-            // [0, TIMEOUT_MS_MAX] milliseconds.
-            //
-            // _thread.Lock.acquire() and _thread.RLock.acquire() raise an
-            // OverflowError if microseconds is greater than PY_TIMEOUT_MAX.
-            milliseconds = TIMEOUT_MS_MAX;
-        }
-        assert(milliseconds != INFINITE);
-    }
-    else {
-        milliseconds = INFINITE;
-    }
-
-    if (EnterNonRecursiveMutex((PNRMUTEX)aLock,
-                               (DWORD)milliseconds) == WAIT_OBJECT_0) {
-        success = PY_LOCK_ACQUIRED;
-    }
-    else {
-        success = PY_LOCK_FAILURE;
-    }
-
-    return success;
-}
-int
-PyThread_acquire_lock(PyThread_type_lock aLock, int waitflag)
-{
-    return PyThread_acquire_lock_timed(aLock, waitflag ? -1 : 0, 0);
-}
-
-void
-PyThread_release_lock(PyThread_type_lock aLock)
-{
-    assert(aLock);
-    (void)LeaveNonRecursiveMutex((PNRMUTEX) aLock);
-}
 
 /* minimum/maximum thread stack sizes supported */
 #define THREAD_MIN_STACKSIZE    0x8000          /* 32 KiB */