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gh-114271: Make _thread.ThreadHandle thread-safe in free-threaded builds (GH-115190)

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Make `_thread.ThreadHandle` thread-safe in free-threaded builds

We protect the mutable state of `ThreadHandle` using a `_PyOnceFlag`.
Concurrent operations (i.e. `join` or `detach`) on `ThreadHandle` block
until it is their turn to execute or an earlier operation succeeds.
Once an operation has been applied successfully all future operations
complete immediately.

The `join()` method is now idempotent. It may be called multiple times
but the underlying OS thread will only be joined once. After `join()`
succeeds, any future calls to `join()` will succeed immediately.

The internal thread handle `detach()` method has been removed.
This commit is contained in:
mpage 2024-03-01 13:43:12 -08:00 • committed by GitHub
parent 5e0c7bc1d3
commit 9e88173d36
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5 changed files with 230 additions and 106 deletions
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13
Include/internal/pycore_lock.h
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@ -136,6 +136,10 @@ typedef struct {
uint8_t v;
} PyEvent;
// Check if the event is set without blocking. Returns 1 if the event is set or
// 0 otherwise.
PyAPI_FUNC(int) _PyEvent_IsSet(PyEvent *evt);
// Set the event and notify any waiting threads.
// Export for '_testinternalcapi' shared extension
PyAPI_FUNC(void) _PyEvent_Notify(PyEvent *evt);
@ -149,6 +153,15 @@ PyAPI_FUNC(void) PyEvent_Wait(PyEvent *evt);
// and 0 if the timeout expired or thread was interrupted.
PyAPI_FUNC(int) PyEvent_WaitTimed(PyEvent *evt, PyTime_t timeout_ns);
// A one-time event notification with reference counting.
typedef struct _PyEventRc {
PyEvent event;
Py_ssize_t refcount;
} _PyEventRc;
_PyEventRc *_PyEventRc_New(void);
void _PyEventRc_Incref(_PyEventRc *erc);
void _PyEventRc_Decref(_PyEventRc *erc);
// _PyRawMutex implements a word-sized mutex that that does not depend on the
// parking lot API, and therefore can be used in the parking lot