CPython's pthread-based thread identifier relies on pthread_t being able
to be represented as an unsigned integer type.
This is true in most Linux libc implementations where it's defined as an
unsigned long, however musl typedefs it as a struct *.
If the pointer has the high bit set and is cast to PyThread_ident_t, the
resultant value can be sign-extended [0]. This can cause issues when
comparing against threading._MainThread's identifier. The main thread's
identifier value is retrieved via _get_main_thread_ident which is backed
by an unsigned long which truncates sign extended bits.
>>> hex(threading.main_thread().ident)
'0xb6f33f3c'
>>> hex(threading.current_thread().ident)
'0xffffffffb6f33f3c'
Work around this by conditionally compiling in some code for non-glibc
based Linux platforms that are at risk of sign-extension to return a
PyLong based on the main thread's unsigned long thread identifier if the
current thread is the main thread.
[0]: https://gcc.gnu.org/onlinedocs/gcc-14.2.0/gcc/Arrays-and-pointers-implementation.html
---------
Signed-off-by: Vincent Fazio <vfazio@gmail.com>
Instead of surprise crashes and memory corruption, we now hang threads that attempt to re-enter the Python interpreter after Python runtime finalization has started. These are typically daemon threads (our long standing mis-feature) but could also be threads spawned by extension modules that then try to call into Python. This marks the `PyThread_exit_thread` public C API as deprecated as there is no plausible safe way to accomplish that on any supported platform in the face of things like C++ code with finalizers anywhere on a thread's stack. Doing this was the least bad option.
Co-authored-by: Gregory P. Smith <greg@krypto.org>
Use the new public Raw functions:
* _PyTime_PerfCounterUnchecked() with PyTime_PerfCounterRaw()
* _PyTime_TimeUnchecked() with PyTime_TimeRaw()
* _PyTime_MonotonicUnchecked() with PyTime_MonotonicRaw()
Remove internal functions:
* _PyTime_PerfCounterUnchecked()
* _PyTime_TimeUnchecked()
* _PyTime_MonotonicUnchecked()
PyTime_t no longer uses an arbitrary unit, it's always a number of
nanoseconds (64-bit signed integer).
* Rename _PyTime_FromNanosecondsObject() to _PyTime_FromLong().
* Rename _PyTime_AsNanosecondsObject() to _PyTime_AsLong().
* Remove pytime_from_nanoseconds().
* Remove pytime_as_nanoseconds().
* Remove _PyTime_FromNanoseconds().
Remove references to the old names _PyTime_MIN
and _PyTime_MAX, now that PyTime_MIN and
PyTime_MAX are public.
Replace also _PyTime_MIN with PyTime_MIN.
<pycore_time.h> include is no longer needed to get the PyTime_t type
in internal header files. This type is now provided by <Python.h>
include. Add <pycore_time.h> includes to C files instead.
This marks dead ThreadHandles as non-joinable earlier in
`PyOS_AfterFork_Child()` before we execute any Python code. The handles
are stored in a global linked list in `_PyRuntimeState` because `fork()`
affects the entire process.
Joining a thread now ensures the underlying OS thread has exited. This is required for safer fork() in multi-threaded processes.
---------
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
* pycore_pythread.h is now the central place to make sure that
_POSIX_THREADS and _POSIX_SEMAPHORES macros are defined if
available.
* Make sure that pycore_pythread.h is included when _POSIX_THREADS
and _POSIX_SEMAPHORES macros are tested.
* PY_TIMEOUT_MAX is now defined as a constant, since its value
depends on _POSIX_THREADS, instead of being defined as a macro.
* Prevent integer overflow in the preprocessor when computing
PY_TIMEOUT_MAX_VALUE on Windows:
replace "0xFFFFFFFELL * 1000 < LLONG_MAX"
with "0xFFFFFFFELL < LLONG_MAX / 1000".
* Document the change and give hints how to fix affected code.
* Add an exception for PY_TIMEOUT_MAX name to smelly.py
* Add PY_TIMEOUT_MAX to the stable ABI
pthread _PyThread_cond_after() implementation now uses the _PyTime_t
type to handle properly overflow: clamp to the maximum value.
Remove MICROSECONDS_TO_TIMESPEC() function.
Reformat the pthread implementation of PyThread_acquire_lock_timed()
using a mutex and a conditioinal variable.
* Add goto to avoid multiple indentation levels and exit quickly
* Use "while(1)" and make the control flow more obvious.
* PEP 7: Add braces around if blocks.
This parallels _PyRuntimeState.interpreters. Doing this helps make it more clear what part of PyInterpreterState relates to its threads.
https://bugs.python.org/issue46008
Add a private C API for deadlines: add _PyDeadline_Init() and
_PyDeadline_Get() functions.
* Add _PyTime_Add() and _PyTime_Mul() functions which compute t1+t2
and t1*t2 and clamp the result on overflow.
* _PyTime_MulDiv() now uses _PyTime_Add() and _PyTime_Mul().
On Unix, if the sem_clockwait() function is available in the C
library (glibc 2.30 and newer), the threading.Lock.acquire() method
now uses the monotonic clock (time.CLOCK_MONOTONIC) for the timeout,
rather than using the system clock (time.CLOCK_REALTIME), to not be
affected by system clock changes.
configure now checks if the sem_clockwait() function is available.
PyThread_acquire_lock_timed() now clamps the timeout into the
[_PyTime_MIN; _PyTime_MAX] range (_PyTime_t type) if it is too large,
rather than calling Py_FatalError() which aborts the process.
PyThread_acquire_lock_timed() no longer uses
MICROSECONDS_TO_TIMESPEC() to compute sem_timedwait() argument, but
_PyTime_GetSystemClock() and _PyTime_AsTimespec_truncate().
Fix _thread.TIMEOUT_MAX value on Windows: the maximum timeout is
0x7FFFFFFF milliseconds (around 24.9 days), not 0xFFFFFFFF
milliseconds (around 49.7 days).
Set PY_TIMEOUT_MAX to 0x7FFFFFFF milliseconds, rather than 0xFFFFFFFF
milliseconds.
Fix PY_TIMEOUT_MAX overflow test: replace (us >= PY_TIMEOUT_MAX) with
(us > PY_TIMEOUT_MAX).
Add the _PyTime_AsTimespec_clamp() function: similar to
_PyTime_AsTimespec(), but clamp to _PyTime_t min/max and don't raise
an exception.
PyThread_acquire_lock_timed() now uses _PyTime_AsTimespec_clamp() to
remove the Py_UNREACHABLE() code path.
* Add _PyTime_AsTime_t() function.
* Add PY_TIME_T_MIN and PY_TIME_T_MAX constants.
* Replace _PyTime_AsTimeval_noraise() with _PyTime_AsTimeval_clamp().
* Add pytime_divide_round_up() function.
* Fix integer overflow in pytime_divide().
* Add pytime_divmod() function.
Rename _PyInterpreterState_GET_UNSAFE() to _PyInterpreterState_GET()
for consistency with _PyThreadState_GET() and to have a shorter name
(help to fit into 80 columns).
Add also "assert(tstate != NULL);" to the function.
Add a private _at_fork_reinit() method to _thread.Lock,
_thread.RLock, threading.RLock and threading.Condition classes:
reinitialize the lock after fork in the child process; reset the lock
to the unlocked state.
Rename also the private _reset_internal_locks() method of
threading.Event to _at_fork_reinit().
* Add _PyThread_at_fork_reinit() private function. It is excluded
from the limited C API.
* threading.Thread._reset_internal_locks() now calls
_at_fork_reinit() on self._tstate_lock rather than creating a new
Python lock object.
This changeset increases the default size of the stack
for threads on macOS to the size of the stack
of the main thread and reenables the relevant
recursion test.
Victor Stinner