gh-110014: Remove PY_TIMEOUT_MAX from limited C API

If the timeout is greater than PY_TIMEOUT_MAX,
PyThread_acquire_lock_timed() uses a timeout of PY_TIMEOUT_MAX
microseconds, which is around 280.6 years. This case is unlikely and
limiting a timeout to 280.6 years sounds like a reasonable trade-off.

The constant PY_TIMEOUT_MAX is not used in PyPI top 5,000 projects.

Doc/whatsnew/3.13.rst

@@ -1290,3 +1290,6 @@ removed, although there is currently no date scheduled for their removal.
   * :c:func:`PyThread_get_key_value`: use :c:func:`PyThread_tss_get`.
   * :c:func:`PyThread_delete_key_value`: use :c:func:`PyThread_tss_delete`.
   * :c:func:`PyThread_ReInitTLS`: no longer needed.
+
+* Remove undocumented ``PY_TIMEOUT_MAX`` constant from the limited C API.
+  (Contributed by Victor Stinner in :gh:`110014`.)

Include/cpython/pythread.h

@@ -2,6 +2,14 @@
 #  error "this header file must not be included directly"
 #endif
 
+// PY_TIMEOUT_MAX is the highest usable value (in microseconds) of PY_TIMEOUT_T
+// type, and depends on the system threading API.
+//
+// NOTE: this isn't the same value as `_thread.TIMEOUT_MAX`. The _thread module
+// exposes a higher-level API, with timeouts expressed in seconds and
+// floating-point numbers allowed.
+PyAPI_DATA(const long long) PY_TIMEOUT_MAX;
+
 #define PYTHREAD_INVALID_THREAD_ID ((unsigned long)-1)
 
 #ifdef HAVE_PTHREAD_H

Include/pythread.h

@@ -33,27 +33,18 @@ PyAPI_FUNC(int) PyThread_acquire_lock(PyThread_type_lock, int);
 #define WAIT_LOCK       1
 #define NOWAIT_LOCK     0
 
-/* PY_TIMEOUT_T is the integral type used to specify timeouts when waiting
-   on a lock (see PyThread_acquire_lock_timed() below).
-   PY_TIMEOUT_MAX is the highest usable value (in microseconds) of that
-   type, and depends on the system threading API.
-
-   NOTE: this isn't the same value as `_thread.TIMEOUT_MAX`.  The _thread
-   module exposes a higher-level API, with timeouts expressed in seconds
-   and floating-point numbers allowed.
-*/
+// PY_TIMEOUT_T is the integral type used to specify timeouts when waiting
+// on a lock (see PyThread_acquire_lock_timed() below).
 #define PY_TIMEOUT_T long long
 
-PyAPI_DATA(const long long) PY_TIMEOUT_MAX;
-
 
 /* If microseconds == 0, the call is non-blocking: it returns immediately
    even when the lock can't be acquired.
    If microseconds > 0, the call waits up to the specified duration.
    If microseconds < 0, the call waits until success (or abnormal failure)
 
-   microseconds must be less than PY_TIMEOUT_MAX. Behaviour otherwise is
-   undefined.
+   If *microseconds* is greater than PY_TIMEOUT_MAX, clamp the timeout to
+   PY_TIMEOUT_MAX microseconds.
 
    If intr_flag is true and the acquire is interrupted by a signal, then the
    call will return PY_LOCK_INTR.  The caller may reattempt to acquire the

Misc/NEWS.d/next/C API/2023-10-02-13-39-57.gh-issue-110014.gfQ4jU.rst

@@ -0,0 +1,2 @@
+Remove undocumented ``PY_TIMEOUT_MAX`` constant from the limited C API.
+Patch by Victor Stinner.

Misc/stable_abi.toml

@@ -1843,10 +1843,6 @@
 [function.PyThread_start_new_thread]
     added = '3.2'
 
-# Not mentioned in PEP 384, was implemented as a macro in Python <= 3.12
-[data.PY_TIMEOUT_MAX]
-    added = '3.2'
-
 # The following were added in PC/python3.def in Python 3.3:
 # 7800f75827b1be557be16f3b18f5170fbf9fae08
 # 9c56409d3353b8cd4cfc19e0467bbe23fd34fc92

Tools/build/smelly.py

@@ -11,11 +11,6 @@
 if sys.platform == 'darwin':
     ALLOWED_PREFIXES += ('__Py',)
 
-# "Legacy": some old symbols are prefixed by "PY_".
-EXCEPTIONS = frozenset({
-    'PY_TIMEOUT_MAX',
-})
-
 IGNORED_EXTENSION = "_ctypes_test"
 # Ignore constructor and destructor functions
 IGNORED_SYMBOLS = {'_init', '_fini'}
@@ -77,7 +72,7 @@ def get_smelly_symbols(stdout):
         symbol = parts[-1]
         result = '%s (type: %s)' % (symbol, symtype)
 
-        if symbol.startswith(ALLOWED_PREFIXES) or symbol in EXCEPTIONS:
+        if symbol.startswith(ALLOWED_PREFIXES):
             python_symbols.append(result)
             continue