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Add new argument to gil_safe_call_once_and_store::call_once_and_store_result

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This commit is contained in:
Xuehai Pan
2025-12-13 20:06:35 +08:00
parent 1006933415
commit 729654cf6f
1 changed files with 18 additions and 11 deletions
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29
include/pybind11/gil_safe_call_once.h
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@@ -8,8 +8,12 @@
#include <cassert>
#include <mutex>
#ifdef Py_GIL_DISABLED
#if defined(Py_GIL_DISABLED) || defined(PYBIND11_HAS_SUBINTERPRETER_SUPPORT)
# include <atomic>
using atomic_bool = std::atomic_bool;
#else
using atomic_bool = bool;
#endif
PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
@@ -53,7 +57,8 @@ class gil_safe_call_once_and_store {
public:
// PRECONDITION: The GIL must be held when `call_once_and_store_result()` is called.
template <typename Callable>
gil_safe_call_once_and_store &call_once_and_store_result(Callable &&fn) {
gil_safe_call_once_and_store &call_once_and_store_result(Callable &&fn,
void (*finalize_fn)(T &) = nullptr) {
if (!is_initialized_) { // This read is guarded by the GIL.
// Multiple threads may enter here, because the GIL is released in the next line and
// CPython API calls in the `fn()` call below may release and reacquire the GIL.
@@ -61,8 +66,9 @@ public:
std::call_once(once_flag_, [&] {
// Only one thread will ever enter here.
gil_scoped_acquire gil_acq;
::new (storage_) T(fn()); // fn may release, but will reacquire, the GIL.
is_initialized_ = true; // This write is guarded by the GIL.
::new (storage_) T(fn()); // fn may release, but will reacquire, the GIL.
finalize_fn_ = finalize_fn; // Store the finalizer.
is_initialized_ = true; // This write is guarded by the GIL.
});
// All threads will observe `is_initialized_` as true here.
}
@@ -83,20 +89,21 @@ public:
}
constexpr gil_safe_call_once_and_store() = default;
PYBIND11_DTOR_CONSTEXPR ~gil_safe_call_once_and_store() = default;
PYBIND11_DTOR_CONSTEXPR ~gil_safe_call_once_and_store() {
if (is_initialized_ && finalize_fn_ != nullptr) {
finalize_fn_(*reinterpret_cast<T *>(storage_));
}
}
private:
alignas(T) char storage_[sizeof(T)] = {};
std::once_flag once_flag_;
#ifdef Py_GIL_DISABLED
std::atomic_bool
#else
bool
#endif
is_initialized_{false};
void (*finalize_fn_)(T &) = nullptr;
// The `is_initialized_`-`storage_` pair is very similar to `std::optional`,
// but the latter does not have the triviality properties of former,
// therefore `std::optional` is not a viable alternative here.
atomic_bool is_initialized_{false};
};
PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)