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gh-113743: Make the MRO cache thread-safe in free-threaded builds (#113930)

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Makes _PyType_Lookup thread safe, including:
    Thread safety of the underlying cache.
    Make mutation of mro and type members thread safe
    Also _PyType_GetMRO and _PyType_GetBases are currently returning borrowed references which aren't safe.
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Dino Viehland 2024-02-15 10:54:57 -08:00 • committed by GitHub
parent e74fa294c9
commit ae460d450a
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11 changed files with 500 additions and 80 deletions
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71
Python/lock.c
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@ -459,3 +459,74 @@ _PyRWMutex_Unlock(_PyRWMutex *rwmutex)
_PyParkingLot_UnparkAll(&rwmutex->bits);
}
}
#define SEQLOCK_IS_UPDATING(sequence) (sequence & 0x01)
void _PySeqLock_LockWrite(_PySeqLock *seqlock)
{
// lock the entry by setting by moving to an odd sequence number
uint32_t prev = _Py_atomic_load_uint32_relaxed(&seqlock->sequence);
while (1) {
if (SEQLOCK_IS_UPDATING(prev)) {
// Someone else is currently updating the cache
_Py_yield();
prev = _Py_atomic_load_uint32_relaxed(&seqlock->sequence);
}
else if (_Py_atomic_compare_exchange_uint32(&seqlock->sequence, &prev, prev + 1)) {
// We've locked the cache
break;
}
else {
_Py_yield();
}
}
}
void _PySeqLock_AbandonWrite(_PySeqLock *seqlock)
{
uint32_t new_seq = seqlock->sequence - 1;
assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq);
}
void _PySeqLock_UnlockWrite(_PySeqLock *seqlock)
{
uint32_t new_seq = seqlock->sequence + 1;
assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq);
}
uint32_t _PySeqLock_BeginRead(_PySeqLock *seqlock)
{
uint32_t sequence = _Py_atomic_load_uint32_acquire(&seqlock->sequence);
while (SEQLOCK_IS_UPDATING(sequence)) {
_Py_yield();
sequence = _Py_atomic_load_uint32_acquire(&seqlock->sequence);
}
return sequence;
}
uint32_t _PySeqLock_EndRead(_PySeqLock *seqlock, uint32_t previous)
{
// Synchronize again and validate that the entry hasn't been updated
// while we were readying the values.
if (_Py_atomic_load_uint32_acquire(&seqlock->sequence) == previous) {
return 1;
}
_Py_yield();
return 0;
}
uint32_t _PySeqLock_AfterFork(_PySeqLock *seqlock)
{
// Synchronize again and validate that the entry hasn't been updated
// while we were readying the values.
if (SEQLOCK_IS_UPDATING(seqlock->sequence)) {
seqlock->sequence = 0;
return 1;
}
return 0;
}