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Description
Crash report
What happened?
Bisected to#24592.
Simple repro:
import_ioclassMyIO(_io.BytesIO):def__init__(self):_io.BytesIO.__init__(self)self.writes= []defwrite(self,b):self.writes.append(b)tw.write("c")returnlen(b)buf=MyIO()tw=_io.TextIOWrapper(buf)CHUNK_SIZE=8192tw.write("a"* (CHUNK_SIZE-1))tw.write("b"*2)tw.flush()assertb''.join(tw.buffer.writes)==b"a"* (CHUNK_SIZE-1)+b"b"*2+b"c"
On debug build it causes C assertion failure:
python: ./Modules/_io/textio.c:1582: _textiowrapper_writeflush: Assertion `PyUnicode_GET_LENGTH(pending) == self->pending_bytes_count' failed.Program received signal SIGABRT, Aborted.__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:5050../sysdeps/unix/sysv/linux/raise.c: No such file or directory.(gdb) bt#0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50#1 0x00007ffff7c84537 in __GI_abort () at abort.c:79#2 0x00007ffff7c8440f in __assert_fail_base (fmt=0x7ffff7dfb688 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=0x555555a24d40 "PyUnicode_GET_LENGTH(pending) == self->pending_bytes_count", file=0x555555a25332 "./Modules/_io/textio.c", line=1582, function=<optimized out>) at assert.c:92#3 0x00007ffff7c93662 in __GI___assert_fail (assertion=assertion@entry=0x555555a24d40 "PyUnicode_GET_LENGTH(pending) == self->pending_bytes_count", file=file@entry=0x555555a25332 "./Modules/_io/textio.c", line=line@entry=1582, function=function@entry=0x555555a256b0 <__PRETTY_FUNCTION__.9> "_textiowrapper_writeflush") at assert.c:101#4 0x00005555559102b9 in _textiowrapper_writeflush (self=self@entry=0x7ffff77896d0) at ./Modules/_io/textio.c:1582#5 0x000055555591065d in _io_TextIOWrapper_flush_impl (self=0x7ffff77896d0) at ./Modules/_io/textio.c:3092#6 0x0000555555910791 in _io_TextIOWrapper_flush (self=<optimized out>, _unused_ignored=<optimized out>) at ./Modules/_io/clinic/textio.c.h:1105#7 0x0000555555693483 in method_vectorcall_NOARGS (func=0x7ffff7731250, args=0x7ffff7fc1070, nargsf=<optimized out>, kwnames=<optimized out>) at Objects/descrobject.c:447#8 0x0000555555680d7c in _PyObject_VectorcallTstate (tstate=0x555555be4678 <_PyRuntime+294136>, callable=0x7ffff7731250, args=0x7ffff7fc1070, nargsf=9223372036854775809, kwnames=0x0) at ./Include/internal/pycore_call.h:168#9 0x0000555555680e97 in PyObject_Vectorcall (callable=callable@entry=0x7ffff7731250, args=args@entry=0x7ffff7fc1070, nargsf=<optimized out>, kwnames=kwnames@entry=0x0) at Objects/call.c:327#10 0x000055555580876d in _PyEval_EvalFrameDefault (tstate=tstate@entry=0x555555be4678 <_PyRuntime+294136>, frame=0x7ffff7fc1020, throwflag=throwflag@entry=0) at Python/generated_cases.c.h:813...If_io.TextIOWrapper.write() tries to store more thanself->chunk_size data inself->pending_bytes, it calls_textiowrapper_writeflush():
Lines 1726 to 1733 inb48a3db
| elseif (self->pending_bytes_count+bytes_len>self->chunk_size) { | |
| // Prevent to concatenate more than chunk_size data. | |
| if (_textiowrapper_writeflush(self)<0) { | |
| Py_DECREF(b); | |
| returnNULL; | |
| } | |
| self->pending_bytes=b; | |
| } |
_textiowrapper_writeflush() flushesself->pending_bytes contents to wrapped buffer throughwrite() method call:Lines 1621 to 1628 inb48a3db
| self->pending_bytes_count=0; | |
| self->pending_bytes=NULL; | |
| Py_DECREF(pending); | |
| PyObject*ret; | |
| do { | |
| ret=PyObject_CallMethodOneArg(self->buffer,&_Py_ID(write),b); | |
| }while (ret==NULL&&_PyIO_trap_eintr()); |
The problem is that call to
write() method can cause_io.TextIOWrapper.write() call (directly, as in repro, or from other thread), which re-setsself->pending_bytes andself->pending_bytes_count values.CPython versions tested on:
3.10, 3.11, 3.12, CPython main branch
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.14.0a0 (heads/main:e94dbe4ed8, May 24 2024, 00:47:49) [GCC 10.2.1 20210110]
Linked PRs
- gh-119506: fix
_io.TextIOWrapper.write()write during flush #119507 - [3.13] gh-119506: fix
_io.TextIOWrapper.write()write during flush (GH-119507) #119964 - [3.12] gh-119506: fix
_io.TextIOWrapper.write()write during flush (GH-119507) #119965 - [3.11] gh-119506: fix _io.TextIOWrapper.write() write during flush (#119507) #120314