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/*
Logic for a better replacement of PyGILState_Ensure().
This version is ready to handle the case of a non-Python-started
thread in which we do a large number of calls to CFFI callbacks. If
we were to rely on PyGILState_Ensure() for that, we would constantly
be creating and destroying PyThreadStates---it is slow, and
PyThreadState_Delete() will actually walk the list of all thread
states, making it O(n). :-(
This version only creates one PyThreadState object the first time we
see a given thread, and keep it alive until the thread is really
shut down, using a destructor on the tls key.
*/
#ifdef WITH_THREAD
#include <pthread.h>
static pthread_key_t cffi_tls_key;
struct cffi_tls_s {
/* The locally-made thread state. This is only non-null in case
we build the thread state here. It remains null if this thread
had already a thread state provided by CPython. */
PyThreadState *local_thread_state;
/* The saved errno. If the C compiler supports '__thread', then
we use that instead; this value is not used at all in this case. */
int saved_errno;
};
static void _tls_destructor(void *p)
{
struct cffi_tls_s *tls = (struct cffi_tls_s *)p;
if (tls->local_thread_state != NULL) {
/* We need to re-acquire the GIL temporarily to free the
thread state. I hope it is not a problem to do it in
a thread-local destructor.
*/
PyEval_RestoreThread(tls->local_thread_state);
PyThreadState_DeleteCurrent();
}
free(tls);
}
static void init_cffi_tls(void)
{
if (pthread_key_create(&cffi_tls_key, _tls_destructor) != 0)
PyErr_SetString(PyExc_OSError, "pthread_key_create() failed");
}
static struct cffi_tls_s *_make_cffi_tls(void)
{
void *p = calloc(1, sizeof(struct cffi_tls_s));
if (p == NULL)
return NULL;
if (pthread_setspecific(cffi_tls_key, p) != 0) {
free(p);
return NULL;
}
return p;
}
static struct cffi_tls_s *get_cffi_tls(void)
{
void *p = pthread_getspecific(cffi_tls_key);
if (p == NULL)
p = _make_cffi_tls();
return (struct cffi_tls_s *)p;
}
/* USE__THREAD is defined by setup.py if it finds that it is
syntactically valid to use "__thread" with this C compiler. */
#ifdef USE__THREAD
static __thread int cffi_saved_errno = 0;
static void save_errno(void) { cffi_saved_errno = errno; }
static void restore_errno(void) { errno = cffi_saved_errno; }
#else
static void save_errno(void)
{
int saved = errno;
struct cffi_tls_s *tls = get_cffi_tls();
if (tls != NULL)
tls->saved_errno = saved;
}
static void restore_errno(void)
{
struct cffi_tls_s *tls = get_cffi_tls();
if (tls != NULL)
errno = tls->saved_errno;
}
#endif
/* Seems that CPython 3.5.1 made our job harder. Did not find out how
to do that without these hacks. We can't use PyThreadState_GET(),
because that calls PyThreadState_Get() which fails an assert if the
result is NULL. */
#ifndef _Py_atomic_load_relaxed /* this was abruptly un-defined in 3.5.1 */
void *volatile _PyThreadState_Current;
/* XXX simple volatile access is assumed atomic */
# define _Py_atomic_load_relaxed(pp) (*(pp))
#endif
static PyThreadState *get_current_ts(void)
{
#if PY_MAJOR_VERSION >= 3
return (PyThreadState*)_Py_atomic_load_relaxed(&_PyThreadState_Current);
#else
return _PyThreadState_Current;
#endif
}
static PyGILState_STATE gil_ensure(void)
{
/* Called at the start of a callback. Replacement for
PyGILState_Ensure().
*/
PyGILState_STATE result;
struct cffi_tls_s *tls;
PyThreadState *ts = PyGILState_GetThisThreadState();
if (ts != NULL) {
ts->gilstate_counter++;
if (ts != get_current_ts()) {
/* common case: 'ts' is our non-current thread state and
we have to make it current and acquire the GIL */
PyEval_RestoreThread(ts);
return PyGILState_UNLOCKED;
}
else {
return PyGILState_LOCKED;
}
}
else {
/* no thread state here so far. */
result = PyGILState_Ensure();
assert(result == PyGILState_UNLOCKED);
ts = PyGILState_GetThisThreadState();
assert(ts != NULL);
assert(ts == get_current_ts());
assert(ts->gilstate_counter >= 1);
/* Save the now-current thread state inside our 'local_thread_state'
field, to be removed at thread shutdown */
tls = get_cffi_tls();
if (tls != NULL) {
tls->local_thread_state = ts;
ts->gilstate_counter++;
}
return result;
}
}
static void gil_release(PyGILState_STATE oldstate)
{
PyGILState_Release(oldstate);
}
#else /* !WITH_THREAD */
static int cffi_saved_errno = 0;
static void save_errno(void) { cffi_saved_errno = errno; }
static void restore_errno(void) { errno = cffi_saved_errno; }
static PyGILState_STATE gil_ensure(void) { return -1; }
static void gil_release(PyGILState_STATE oldstate) { }
#endif /* !WITH_THREAD */
#define save_errno_only save_errno
#define restore_errno_only restore_errno
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