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Commit0841606

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[3.13]gh-119247: Add macros to use PySequence_Fast safely in free-threaded build (GH-119315) (#119419)
Add `Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST` and`Py_END_CRITICAL_SECTION_SEQUENCE_FAST` macros and update `str.join` to usethem. Also add a regression test that would crash reliably without thispatch.(cherry picked from commitbaf347d)Co-authored-by: Josh {*()} Rosenberg <26495692+MojoVampire@users.noreply.github.com>
1 parentcd39da7 commit0841606

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4 files changed

+106
-3
lines changed

4 files changed

+106
-3
lines changed

‎Include/internal/pycore_critical_section.h‎

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Original file line numberDiff line numberDiff line change
@@ -108,6 +108,26 @@ extern "C" {
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_PyCriticalSection2_End(&_cs2); \
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}
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// Specialized version of critical section locking to safely use
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// PySequence_Fast APIs without the GIL. For performance, the argument *to*
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// PySequence_Fast() is provided to the macro, not the *result* of
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// PySequence_Fast(), which would require an extra test to determine if the
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// lock must be acquired.
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# definePy_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(original) \
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{ \
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PyObject *_orig_seq = _PyObject_CAST(original); \
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const bool _should_lock_cs = PyList_CheckExact(_orig_seq); \
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_PyCriticalSection _cs; \
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if (_should_lock_cs) { \
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_PyCriticalSection_Begin(&_cs, &_orig_seq->ob_mutex); \
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}
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# definePy_END_CRITICAL_SECTION_SEQUENCE_FAST() \
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if (_should_lock_cs) { \
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_PyCriticalSection_End(&_cs); \
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} \
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}
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// Asserts that the mutex is locked. The mutex must be held by the
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// top-most critical section otherwise there's the possibility
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// that the mutex would be swalled out in some code paths.
@@ -137,6 +157,8 @@ extern "C" {
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# definePy_END_CRITICAL_SECTION()
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# definePy_BEGIN_CRITICAL_SECTION2(a,b)
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# definePy_END_CRITICAL_SECTION2()
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# definePy_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(original)
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# definePy_END_CRITICAL_SECTION_SEQUENCE_FAST()
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# define_Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex)
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# define_Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)
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#endif/* !Py_GIL_DISABLED */
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@@ -0,0 +1,75 @@
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importsys
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importunittest
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fromitertoolsimportcycle
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fromthreadingimportEvent,Thread
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fromunittestimportTestCase
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fromtest.supportimportthreading_helper
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@threading_helper.requires_working_threading()
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classTestStr(TestCase):
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deftest_racing_join_extend(self):
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'''Test joining a string being extended by another thread'''
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l= []
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ITERS=100
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READERS=10
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done_event=Event()
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defwriter_func():
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foriinrange(ITERS):
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l.extend(map(str,range(i)))
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l.clear()
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done_event.set()
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defreader_func():
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whilenotdone_event.is_set():
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''.join(l)
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writer=Thread(target=writer_func)
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readers= []
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forxinrange(READERS):
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reader=Thread(target=reader_func)
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readers.append(reader)
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reader.start()
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writer.start()
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writer.join()
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forreaderinreaders:
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reader.join()
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deftest_racing_join_replace(self):
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'''
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Test joining a string of characters being replaced with ephemeral
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strings by another thread.
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'''
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l= [*'abcdefg']
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MAX_ORDINAL=1_000
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READERS=10
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done_event=Event()
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defwriter_func():
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fori,cinzip(cycle(range(len(l))),
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map(chr,range(128,MAX_ORDINAL))):
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l[i]=c
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done_event.set()
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defreader_func():
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whilenotdone_event.is_set():
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''.join(l)
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''.join(l)
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''.join(l)
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''.join(l)
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writer=Thread(target=writer_func)
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readers= []
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forxinrange(READERS):
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reader=Thread(target=reader_func)
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readers.append(reader)
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reader.start()
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writer.start()
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writer.join()
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forreaderinreaders:
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reader.join()
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if__name__=="__main__":
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unittest.main()
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@@ -0,0 +1,4 @@
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Added ``Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST`` and
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``Py_END_CRITICAL_SECTION_SEQUENCE_FAST`` macros to make it possible to use
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PySequence_Fast APIs safely when free-threaded, and update str.join to work
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without the GIL using them.

‎Objects/unicodeobject.c‎

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -44,6 +44,7 @@ OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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#include"pycore_bytesobject.h"// _PyBytes_Repeat()
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#include"pycore_ceval.h"// _PyEval_GetBuiltin()
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#include"pycore_codecs.h"// _PyCodec_Lookup()
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#include"pycore_critical_section.h"// Py_*_CRITICAL_SECTION_SEQUENCE_FAST
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#include"pycore_format.h"// F_LJUST
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#include"pycore_initconfig.h"// _PyStatus_OK()
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#include"pycore_interp.h"// PyInterpreterState.fs_codec
@@ -9559,13 +9560,14 @@ PyUnicode_Join(PyObject *separator, PyObject *seq)
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returnNULL;
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}
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/* NOTE: the following code can't call back into Python code,
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* so we are sure that fseq won't be mutated.
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*/
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Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(seq);
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items=PySequence_Fast_ITEMS(fseq);
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seqlen=PySequence_Fast_GET_SIZE(fseq);
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res=_PyUnicode_JoinArray(separator,items,seqlen);
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Py_END_CRITICAL_SECTION_SEQUENCE_FAST();
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Py_DECREF(fseq);
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returnres;
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}

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