gh-108724: Add PyMutex and _PyParkingLot APIs (gh-109344)

PyMutex is a one byte lock with fast, inlineable lock and unlock functions for the common uncontended case.  The design is based on WebKit's WTF::Lock.

PyMutex is built using the _PyParkingLot APIs, which provides a cross-platform futex-like API (based on WebKit's WTF::ParkingLot).  This internal API will be used for building other synchronization primitives used to implement PEP 703, such as one-time initialization and events.

This also includes tests and a mini benchmark in Tools/lockbench/lockbench.py to compare with the existing PyThread_type_lock.

Uncontended acquisition + release:
* Linux (x86-64): PyMutex: 11 ns, PyThread_type_lock: 44 ns
* macOS (arm64): PyMutex: 13 ns, PyThread_type_lock: 18 ns
* Windows (x86-64): PyMutex: 13 ns, PyThread_type_lock: 38 ns

PR Overview:

The primary purpose of this PR is to implement PyMutex, but there are a number of support pieces (described below).

* PyMutex:  A 1-byte lock that doesn't require memory allocation to initialize and is generally faster than the existing PyThread_type_lock.  The API is internal only for now.
* _PyParking_Lot:  A futex-like API based on the API of the same name in WebKit.  Used to implement PyMutex.
* _PyRawMutex:  A word sized lock used to implement _PyParking_Lot.
* PyEvent:  A one time event.  This was used a bunch in the "nogil" fork and is useful for testing the PyMutex implementation, so I've included it as part of the PR.
* pycore_llist.h:  Defines common operations on doubly-linked list.  Not strictly necessary (could do the list operations manually), but they come up frequently in the "nogil" fork. ( Similar to https://man.freebsd.org/cgi/man.cgi?queue)

---------

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

1 files changed, 4 insertions, 7 deletions

diff --git a/configure.ac b/configure.ac
index 34958a1..205a98a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6970,7 +6970,7 @@ fi
 #
 # Avoid #include <Python.h> or #include <pyport.h>. The <Python.h> header
 # requires <pyconfig.h> header which is only written below by AC_OUTPUT below.
-# If the check is done after AC_OUTPUT, modifying LIBATOMIC has no effect
+# If the check is done after AC_OUTPUT, modifying LIBS has no effect
 # anymore.  <pyport.h> cannot be included alone, it's designed to be included
 # by <Python.h>: it expects other includes and macros to be defined.
 _SAVE_VAR([CPPFLAGS])
@@ -6993,7 +6993,7 @@ typedef intptr_t Py_ssize_t;
 #  error "unable to define Py_ssize_t"
 #endif
 
-#include "cpython/pyatomic.h"
+#include "pyatomic.h"
 
 int main()
 {
@@ -7014,7 +7014,7 @@ int main()
 ])
 
 AS_VAR_IF([ac_cv_libatomic_needed], [yes],
-          [LIBATOMIC=${LIBATOMIC-"-latomic"}])
+          [LIBS="${LIBS} -latomic"])
 _RESTORE_VAR([CPPFLAGS])
 
 
@@ -7286,10 +7286,7 @@ PY_STDLIB_MOD([_hashlib], [], [test "$ac_cv_working_openssl_hashlib" = yes],
   [$OPENSSL_INCLUDES], [$OPENSSL_LDFLAGS $OPENSSL_LDFLAGS_RPATH $LIBCRYPTO_LIBS])
 
 dnl test modules
-PY_STDLIB_MOD([_testcapi],
-    [test "$TEST_MODULES" = yes],  []
-    dnl Modules/_testcapi/pyatomic.c uses <cpython/pyatomic.h> header
-    [], [], [$LIBATOMIC])
+PY_STDLIB_MOD([_testcapi], [test "$TEST_MODULES" = yes])
 PY_STDLIB_MOD([_testclinic], [test "$TEST_MODULES" = yes])
 PY_STDLIB_MOD([_testclinic_limited], [test "$TEST_MODULES" = yes])
 PY_STDLIB_MOD([_testinternalcapi], [test "$TEST_MODULES" = yes])