diff options
Diffstat (limited to 'Python/ceval_gil.h')
| -rw-r--r-- | Python/ceval_gil.h | 333 |
1 files changed, 0 insertions, 333 deletions
diff --git a/Python/ceval_gil.h b/Python/ceval_gil.h deleted file mode 100644 index 4c71edd..0000000 --- a/Python/ceval_gil.h +++ /dev/null @@ -1,333 +0,0 @@ -/* - * Implementation of the Global Interpreter Lock (GIL). - */ - -#include <stdlib.h> -#include <errno.h> - -#include "pycore_atomic.h" - - -/* - Notes about the implementation: - - - The GIL is just a boolean variable (locked) whose access is protected - by a mutex (gil_mutex), and whose changes are signalled by a condition - variable (gil_cond). gil_mutex is taken for short periods of time, - and therefore mostly uncontended. - - - In the GIL-holding thread, the main loop (PyEval_EvalFrameEx) must be - able to release the GIL on demand by another thread. A volatile boolean - variable (gil_drop_request) is used for that purpose, which is checked - at every turn of the eval loop. That variable is set after a wait of - `interval` microseconds on `gil_cond` has timed out. - - [Actually, another volatile boolean variable (eval_breaker) is used - which ORs several conditions into one. Volatile booleans are - sufficient as inter-thread signalling means since Python is run - on cache-coherent architectures only.] - - - A thread wanting to take the GIL will first let pass a given amount of - time (`interval` microseconds) before setting gil_drop_request. This - encourages a defined switching period, but doesn't enforce it since - opcodes can take an arbitrary time to execute. - - The `interval` value is available for the user to read and modify - using the Python API `sys.{get,set}switchinterval()`. - - - When a thread releases the GIL and gil_drop_request is set, that thread - ensures that another GIL-awaiting thread gets scheduled. - It does so by waiting on a condition variable (switch_cond) until - the value of last_holder is changed to something else than its - own thread state pointer, indicating that another thread was able to - take the GIL. - - This is meant to prohibit the latency-adverse behaviour on multi-core - machines where one thread would speculatively release the GIL, but still - run and end up being the first to re-acquire it, making the "timeslices" - much longer than expected. - (Note: this mechanism is enabled with FORCE_SWITCHING above) -*/ - -#include "condvar.h" - -#define MUTEX_INIT(mut) \ - if (PyMUTEX_INIT(&(mut))) { \ - Py_FatalError("PyMUTEX_INIT(" #mut ") failed"); }; -#define MUTEX_FINI(mut) \ - if (PyMUTEX_FINI(&(mut))) { \ - Py_FatalError("PyMUTEX_FINI(" #mut ") failed"); }; -#define MUTEX_LOCK(mut) \ - if (PyMUTEX_LOCK(&(mut))) { \ - Py_FatalError("PyMUTEX_LOCK(" #mut ") failed"); }; -#define MUTEX_UNLOCK(mut) \ - if (PyMUTEX_UNLOCK(&(mut))) { \ - Py_FatalError("PyMUTEX_UNLOCK(" #mut ") failed"); }; - -#define COND_INIT(cond) \ - if (PyCOND_INIT(&(cond))) { \ - Py_FatalError("PyCOND_INIT(" #cond ") failed"); }; -#define COND_FINI(cond) \ - if (PyCOND_FINI(&(cond))) { \ - Py_FatalError("PyCOND_FINI(" #cond ") failed"); }; -#define COND_SIGNAL(cond) \ - if (PyCOND_SIGNAL(&(cond))) { \ - Py_FatalError("PyCOND_SIGNAL(" #cond ") failed"); }; -#define COND_WAIT(cond, mut) \ - if (PyCOND_WAIT(&(cond), &(mut))) { \ - Py_FatalError("PyCOND_WAIT(" #cond ") failed"); }; -#define COND_TIMED_WAIT(cond, mut, microseconds, timeout_result) \ - { \ - int r = PyCOND_TIMEDWAIT(&(cond), &(mut), (microseconds)); \ - if (r < 0) \ - Py_FatalError("PyCOND_WAIT(" #cond ") failed"); \ - if (r) /* 1 == timeout, 2 == impl. can't say, so assume timeout */ \ - timeout_result = 1; \ - else \ - timeout_result = 0; \ - } \ - - -#define DEFAULT_INTERVAL 5000 - -static void _gil_initialize(struct _gil_runtime_state *gil) -{ - _Py_atomic_int uninitialized = {-1}; - gil->locked = uninitialized; - gil->interval = DEFAULT_INTERVAL; -} - -static int gil_created(struct _gil_runtime_state *gil) -{ - return (_Py_atomic_load_explicit(&gil->locked, _Py_memory_order_acquire) >= 0); -} - -static void create_gil(struct _gil_runtime_state *gil) -{ - MUTEX_INIT(gil->mutex); -#ifdef FORCE_SWITCHING - MUTEX_INIT(gil->switch_mutex); -#endif - COND_INIT(gil->cond); -#ifdef FORCE_SWITCHING - COND_INIT(gil->switch_cond); -#endif - _Py_atomic_store_relaxed(&gil->last_holder, 0); - _Py_ANNOTATE_RWLOCK_CREATE(&gil->locked); - _Py_atomic_store_explicit(&gil->locked, 0, _Py_memory_order_release); -} - -static void destroy_gil(struct _gil_runtime_state *gil) -{ - /* some pthread-like implementations tie the mutex to the cond - * and must have the cond destroyed first. - */ - COND_FINI(gil->cond); - MUTEX_FINI(gil->mutex); -#ifdef FORCE_SWITCHING - COND_FINI(gil->switch_cond); - MUTEX_FINI(gil->switch_mutex); -#endif - _Py_atomic_store_explicit(&gil->locked, -1, - _Py_memory_order_release); - _Py_ANNOTATE_RWLOCK_DESTROY(&gil->locked); -} - -#ifdef HAVE_FORK -static void recreate_gil(struct _gil_runtime_state *gil) -{ - _Py_ANNOTATE_RWLOCK_DESTROY(&gil->locked); - /* XXX should we destroy the old OS resources here? */ - create_gil(gil); -} -#endif - -static void -drop_gil(struct _ceval_runtime_state *ceval, struct _ceval_state *ceval2, - PyThreadState *tstate) -{ - struct _gil_runtime_state *gil = &ceval->gil; - if (!_Py_atomic_load_relaxed(&gil->locked)) { - Py_FatalError("drop_gil: GIL is not locked"); - } - - /* tstate is allowed to be NULL (early interpreter init) */ - if (tstate != NULL) { - /* Sub-interpreter support: threads might have been switched - under our feet using PyThreadState_Swap(). Fix the GIL last - holder variable so that our heuristics work. */ - _Py_atomic_store_relaxed(&gil->last_holder, (uintptr_t)tstate); - } - - MUTEX_LOCK(gil->mutex); - _Py_ANNOTATE_RWLOCK_RELEASED(&gil->locked, /*is_write=*/1); - _Py_atomic_store_relaxed(&gil->locked, 0); - COND_SIGNAL(gil->cond); - MUTEX_UNLOCK(gil->mutex); - -#ifdef FORCE_SWITCHING - if (_Py_atomic_load_relaxed(&ceval2->gil_drop_request) && tstate != NULL) { - MUTEX_LOCK(gil->switch_mutex); - /* Not switched yet => wait */ - if (((PyThreadState*)_Py_atomic_load_relaxed(&gil->last_holder)) == tstate) - { - assert(is_tstate_valid(tstate)); - RESET_GIL_DROP_REQUEST(tstate->interp); - /* NOTE: if COND_WAIT does not atomically start waiting when - releasing the mutex, another thread can run through, take - the GIL and drop it again, and reset the condition - before we even had a chance to wait for it. */ - COND_WAIT(gil->switch_cond, gil->switch_mutex); - } - MUTEX_UNLOCK(gil->switch_mutex); - } -#endif -} - - -/* Check if a Python thread must exit immediately, rather than taking the GIL - if Py_Finalize() has been called. - - When this function is called by a daemon thread after Py_Finalize() has been - called, the GIL does no longer exist. - - tstate must be non-NULL. */ -static inline int -tstate_must_exit(PyThreadState *tstate) -{ - /* bpo-39877: Access _PyRuntime directly rather than using - tstate->interp->runtime to support calls from Python daemon threads. - After Py_Finalize() has been called, tstate can be a dangling pointer: - point to PyThreadState freed memory. */ - PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(&_PyRuntime); - return (finalizing != NULL && finalizing != tstate); -} - - -/* Take the GIL. - - The function saves errno at entry and restores its value at exit. - - tstate must be non-NULL. */ -static void -take_gil(PyThreadState *tstate) -{ - int err = errno; - - assert(tstate != NULL); - - if (tstate_must_exit(tstate)) { - /* bpo-39877: If Py_Finalize() has been called and tstate is not the - thread which called Py_Finalize(), exit immediately the thread. - - This code path can be reached by a daemon thread after Py_Finalize() - completes. In this case, tstate is a dangling pointer: points to - PyThreadState freed memory. */ - PyThread_exit_thread(); - } - - assert(is_tstate_valid(tstate)); - PyInterpreterState *interp = tstate->interp; - struct _ceval_runtime_state *ceval = &interp->runtime->ceval; - struct _ceval_state *ceval2 = &interp->ceval; - struct _gil_runtime_state *gil = &ceval->gil; - - /* Check that _PyEval_InitThreads() was called to create the lock */ - assert(gil_created(gil)); - - MUTEX_LOCK(gil->mutex); - - if (!_Py_atomic_load_relaxed(&gil->locked)) { - goto _ready; - } - - while (_Py_atomic_load_relaxed(&gil->locked)) { - unsigned long saved_switchnum = gil->switch_number; - - unsigned long interval = (gil->interval >= 1 ? gil->interval : 1); - int timed_out = 0; - COND_TIMED_WAIT(gil->cond, gil->mutex, interval, timed_out); - - /* If we timed out and no switch occurred in the meantime, it is time - to ask the GIL-holding thread to drop it. */ - if (timed_out && - _Py_atomic_load_relaxed(&gil->locked) && - gil->switch_number == saved_switchnum) - { - if (tstate_must_exit(tstate)) { - MUTEX_UNLOCK(gil->mutex); - PyThread_exit_thread(); - } - assert(is_tstate_valid(tstate)); - - SET_GIL_DROP_REQUEST(interp); - } - } - -_ready: -#ifdef FORCE_SWITCHING - /* This mutex must be taken before modifying gil->last_holder: - see drop_gil(). */ - MUTEX_LOCK(gil->switch_mutex); -#endif - /* We now hold the GIL */ - _Py_atomic_store_relaxed(&gil->locked, 1); - _Py_ANNOTATE_RWLOCK_ACQUIRED(&gil->locked, /*is_write=*/1); - - if (tstate != (PyThreadState*)_Py_atomic_load_relaxed(&gil->last_holder)) { - _Py_atomic_store_relaxed(&gil->last_holder, (uintptr_t)tstate); - ++gil->switch_number; - } - -#ifdef FORCE_SWITCHING - COND_SIGNAL(gil->switch_cond); - MUTEX_UNLOCK(gil->switch_mutex); -#endif - - if (tstate_must_exit(tstate)) { - /* bpo-36475: If Py_Finalize() has been called and tstate is not - the thread which called Py_Finalize(), exit immediately the - thread. - - This code path can be reached by a daemon thread which was waiting - in take_gil() while the main thread called - wait_for_thread_shutdown() from Py_Finalize(). */ - MUTEX_UNLOCK(gil->mutex); - drop_gil(ceval, ceval2, tstate); - PyThread_exit_thread(); - } - assert(is_tstate_valid(tstate)); - - if (_Py_atomic_load_relaxed(&ceval2->gil_drop_request)) { - RESET_GIL_DROP_REQUEST(interp); - } - else { - /* bpo-40010: eval_breaker should be recomputed to be set to 1 if there - is a pending signal: signal received by another thread which cannot - handle signals. - - Note: RESET_GIL_DROP_REQUEST() calls COMPUTE_EVAL_BREAKER(). */ - COMPUTE_EVAL_BREAKER(interp, ceval, ceval2); - } - - /* Don't access tstate if the thread must exit */ - if (tstate->async_exc != NULL) { - _PyEval_SignalAsyncExc(tstate->interp); - } - - MUTEX_UNLOCK(gil->mutex); - - errno = err; -} - -void _PyEval_SetSwitchInterval(unsigned long microseconds) -{ - struct _gil_runtime_state *gil = &_PyRuntime.ceval.gil; - gil->interval = microseconds; -} - -unsigned long _PyEval_GetSwitchInterval() -{ - struct _gil_runtime_state *gil = &_PyRuntime.ceval.gil; - return gil->interval; -} |