Merged revisions 68460 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk ........ r68460 | kristjan.jonsson | 2009-01-09 14:31:26 -0600 (Fri, 09 Jan 2009) | 1 line Issue 4293: Make Py_AddPendingCall() thread safe ........
This commit is contained in:
Benjamin Peterson
parent
92d0a6a559
commit
e5bf383959
168
Python/ceval.c
168
Python/ceval.c
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@ -205,6 +205,7 @@ PyEval_GetCallStats(PyObject *self)
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#include "pythread.h"
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static PyThread_type_lock interpreter_lock = 0; /* This is the GIL */
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static PyThread_type_lock pending_lock = 0; /* for pending calls */
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static long main_thread = 0;
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int
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@ -276,6 +277,7 @@ PyEval_ReInitThreads(void)
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adding a new function to each thread_*.h. Instead, just
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create a new lock and waste a little bit of memory */
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interpreter_lock = PyThread_allocate_lock();
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pending_lock = PyThread_allocate_lock();
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PyThread_acquire_lock(interpreter_lock, 1);
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main_thread = PyThread_get_thread_ident();
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@ -348,19 +350,145 @@ PyEval_RestoreThread(PyThreadState *tstate)
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#ifdef WITH_THREAD
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Any thread can schedule pending calls, but only the main thread
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will execute them.
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There is no facility to schedule calls to a particular thread, but
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that should be easy to change, should that ever be required. In
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that case, the static variables here should go into the python
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threadstate.
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#endif
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*/
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#ifdef WITH_THREAD
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/* The WITH_THREAD implementation is thread-safe. It allows
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scheduling to be made from any thread, and even from an executing
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callback.
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*/
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#define NPENDINGCALLS 32
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static struct {
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int (*func)(void *);
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void *arg;
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} pendingcalls[NPENDINGCALLS];
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static int pendingfirst = 0;
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static int pendinglast = 0;
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static volatile int pendingcalls_to_do = 1; /* trigger initialization of lock */
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static char pendingbusy = 0;
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int
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Py_AddPendingCall(int (*func)(void *), void *arg)
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{
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int i, j, result=0;
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PyThread_type_lock lock = pending_lock;
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/* try a few times for the lock. Since this mechanism is used
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* for signal handling (on the main thread), there is a (slim)
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* chance that a signal is delivered on the same thread while we
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* hold the lock during the Py_MakePendingCalls() function.
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* This avoids a deadlock in that case.
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* Note that signals can be delivered on any thread. In particular,
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* on Windows, a SIGINT is delivered on a system-created worker
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* thread.
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* We also check for lock being NULL, in the unlikely case that
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* this function is called before any bytecode evaluation takes place.
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*/
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if (lock != NULL) {
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for (i = 0; i<100; i++) {
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if (PyThread_acquire_lock(lock, NOWAIT_LOCK))
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break;
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}
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if (i == 100)
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return -1;
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}
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i = pendinglast;
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j = (i + 1) % NPENDINGCALLS;
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if (j == pendingfirst) {
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result = -1; /* Queue full */
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} else {
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pendingcalls[i].func = func;
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pendingcalls[i].arg = arg;
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pendinglast = j;
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}
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/* signal main loop */
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_Py_Ticker = 0;
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pendingcalls_to_do = 1;
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if (lock != NULL)
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PyThread_release_lock(lock);
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return result;
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}
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int
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Py_MakePendingCalls(void)
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{
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int i;
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int r = 0;
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if (!pending_lock) {
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/* initial allocation of the lock */
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pending_lock = PyThread_allocate_lock();
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if (pending_lock == NULL)
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return -1;
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}
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/* only service pending calls on main thread */
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if (main_thread && PyThread_get_thread_ident() != main_thread)
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return 0;
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/* don't perform recursive pending calls */
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if (pendingbusy)
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return 0;
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pendingbusy = 1;
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/* perform a bounded number of calls, in case of recursion */
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for (i=0; i<NPENDINGCALLS; i++) {
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int j;
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int (*func)(void *);
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void *arg;
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/* pop one item off the queue while holding the lock */
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PyThread_acquire_lock(pending_lock, WAIT_LOCK);
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j = pendingfirst;
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if (j == pendinglast) {
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func = NULL; /* Queue empty */
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} else {
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func = pendingcalls[j].func;
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arg = pendingcalls[j].arg;
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pendingfirst = (j + 1) % NPENDINGCALLS;
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}
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pendingcalls_to_do = pendingfirst != pendinglast;
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PyThread_release_lock(pending_lock);
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/* having released the lock, perform the callback */
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if (func == NULL)
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break;
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r = func(arg);
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if (r)
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break;
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}
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pendingbusy = 0;
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return r;
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}
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#else /* if ! defined WITH_THREAD */
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/*
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WARNING! ASYNCHRONOUSLY EXECUTING CODE!
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This code is used for signal handling in python that isn't built
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with WITH_THREAD.
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Don't use this implementation when Py_AddPendingCalls() can happen
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on a different thread!
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XXX WARNING! ASYNCHRONOUSLY EXECUTING CODE!
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There are two possible race conditions:
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(1) nested asynchronous registry calls;
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(2) registry calls made while pending calls are being processed.
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While (1) is very unlikely, (2) is a real possibility.
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(1) nested asynchronous calls to Py_AddPendingCall()
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(2) AddPendingCall() calls made while pending calls are being processed.
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(1) is very unlikely because typically signal delivery
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is blocked during signal handling. So it should be impossible.
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(2) is a real possibility.
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The current code is safe against (2), but not against (1).
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The safety against (2) is derived from the fact that only one
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thread (the main thread) ever takes things out of the queue.
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XXX Darn! With the advent of thread state, we should have an array
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of pending calls per thread in the thread state! Later...
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thread is present, interrupted by signals, and that the critical
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section is protected with the "busy" variable. On Windows, which
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delivers SIGINT on a system thread, this does not hold and therefore
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Windows really shouldn't use this version.
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The two threads could theoretically wiggle around the "busy" variable.
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*/
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#define NPENDINGCALLS 32
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@ -370,7 +498,7 @@ static struct {
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} pendingcalls[NPENDINGCALLS];
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static volatile int pendingfirst = 0;
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static volatile int pendinglast = 0;
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static volatile int things_to_do = 0;
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static volatile int pendingcalls_to_do = 0;
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int
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Py_AddPendingCall(int (*func)(void *), void *arg)
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@ -378,8 +506,6 @@ Py_AddPendingCall(int (*func)(void *), void *arg)
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static volatile int busy = 0;
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int i, j;
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/* XXX Begin critical section */
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/* XXX If you want this to be safe against nested
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XXX asynchronous calls, you'll have to work harder! */
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if (busy)
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return -1;
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busy = 1;
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@ -394,7 +520,7 @@ Py_AddPendingCall(int (*func)(void *), void *arg)
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pendinglast = j;
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_Py_Ticker = 0;
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things_to_do = 1; /* Signal main loop */
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pendingcalls_to_do = 1; /* Signal main loop */
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busy = 0;
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/* XXX End critical section */
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return 0;
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@ -404,14 +530,10 @@ int
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Py_MakePendingCalls(void)
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{
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static int busy = 0;
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#ifdef WITH_THREAD
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if (main_thread && PyThread_get_thread_ident() != main_thread)
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return 0;
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#endif
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if (busy)
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return 0;
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busy = 1;
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things_to_do = 0;
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pendingcalls_to_do = 0;
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for (;;) {
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int i;
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int (*func)(void *);
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@ -424,7 +546,7 @@ Py_MakePendingCalls(void)
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pendingfirst = (i + 1) % NPENDINGCALLS;
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if (func(arg) < 0) {
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busy = 0;
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things_to_do = 1; /* We're not done yet */
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pendingcalls_to_do = 1; /* We're not done yet */
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return -1;
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}
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}
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@ -432,6 +554,8 @@ Py_MakePendingCalls(void)
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return 0;
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}
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#endif /* WITH_THREAD */
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/* The interpreter's recursion limit */
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@ -518,7 +642,7 @@ static int _Py_TracingPossible = 0;
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/* for manipulating the thread switch and periodic "stuff" - used to be
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per thread, now just a pair o' globals */
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int _Py_CheckInterval = 100;
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volatile int _Py_Ticker = 100;
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volatile int _Py_Ticker = 0; /* so that we hit a "tick" first thing */
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PyObject *
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PyEval_EvalCode(PyCodeObject *co, PyObject *globals, PyObject *locals)
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@ -903,7 +1027,7 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
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/* Do periodic things. Doing this every time through
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the loop would add too much overhead, so we do it
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only every Nth instruction. We also do it if
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``things_to_do'' is set, i.e. when an asynchronous
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``pendingcalls_to_do'' is set, i.e. when an asynchronous
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event needs attention (e.g. a signal handler or
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async I/O handler); see Py_AddPendingCall() and
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Py_MakePendingCalls() above. */
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@ -919,12 +1043,12 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
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#ifdef WITH_TSC
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ticked = 1;
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#endif
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if (things_to_do) {
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if (pendingcalls_to_do) {
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if (Py_MakePendingCalls() < 0) {
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why = WHY_EXCEPTION;
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goto on_error;
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}
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if (things_to_do)
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if (pendingcalls_to_do)
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/* MakePendingCalls() didn't succeed.
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Force early re-execution of this
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"periodic" code, possibly after
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