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GH-95909: Make _PyArg_Parser initialization thread safe #95958

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Merged
miss-islington merged 6 commits into from
Aug 16, 2022
Merged

GH-95909: Make _PyArg_Parser initialization thread safe #95958

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ab5eecc
add locking
kumaraditya303 Aug 13, 2022
242efec
fix type
kumaraditya303 Aug 15, 2022
36243aa
fix lock
kumaraditya303 Aug 15, 2022
58e6b55
remove atomics
kumaraditya303 Aug 16, 2022
4c6ffcf
refactor
kumaraditya303 Aug 16, 2022
47da017
fix style
kumaraditya303 Aug 16, 2022
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refactor
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@kumaraditya303
kumaraditya303 authored Aug 16, 2022
commit 4c6ffcf0a1bc5425674f8bad32aaabd362dcba60
44 changes: 24 additions & 20 deletions Python/getargs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1973,25 +1973,11 @@ new_kwtuple(const char * const *keywords, int total, int pos)
return kwtuple;
}

static int
parser_init(struct _PyArg_Parser *parser)
static inline int
_parser_init(struct _PyArg_Parser *parser)
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{
const char * const *keywords = parser->keywords;
assert(keywords != NULL);
// volatile as it can be modified by other threads
if (*((volatile int *)&parser->initialized)) {
assert(parser->kwtuple != NULL);
return 1;
}
PyThread_acquire_lock(_PyRuntime.getargs.mutex, WAIT_LOCK);
// Check again if another thread initialized the parser
// while we were waiting for the lock.
if (*((volatile int *)&parser->initialized)) {
assert(parser->kwtuple != NULL);
PyThread_release_lock(_PyRuntime.getargs.mutex);
return 1;
}

assert(parser->pos == 0 &&
(parser->format == NULL || parser->fname == NULL) &&
parser->custom_msg == NULL &&
Expand All @@ -2000,7 +1986,6 @@ parser_init(struct _PyArg_Parser *parser)

int len, pos;
if (scan_keywords(keywords, &len, &pos) < 0) {
PyThread_release_lock(_PyRuntime.getargs.mutex);
return 0;
}

Expand All @@ -2010,7 +1995,6 @@ parser_init(struct _PyArg_Parser *parser)
assert(parser->fname == NULL);
if (parse_format(parser->format, len, pos,
&fname, &custommsg, &min, &max) < 0) {
PyThread_release_lock(_PyRuntime.getargs.mutex);
return 0;
}
}
Expand All @@ -2024,7 +2008,6 @@ parser_init(struct _PyArg_Parser *parser)
if (kwtuple == NULL) {
kwtuple = new_kwtuple(keywords, len, pos);
if (kwtuple == NULL) {
PyThread_release_lock(_PyRuntime.getargs.mutex);
return 0;
}
owned = 1;
Expand All @@ -2043,10 +2026,31 @@ parser_init(struct _PyArg_Parser *parser)
parser->next = static_arg_parsers;
static_arg_parsers = parser;
parser->initialized = owned ? 1 : -1;
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PyThread_release_lock(_PyRuntime.getargs.mutex);
return 1;
}

static int
parser_init(struct _PyArg_Parser *parser)
{
// volatile as it can be modified by other threads
// and should not be optimized or reordered by compiler
if (*((volatile int *)&parser->initialized)) {
assert(parser->kwtuple != NULL);
return 1;
}
PyThread_acquire_lock(_PyRuntime.getargs.mutex, WAIT_LOCK);
// Check again if another thread initialized the parser
// while we were waiting for the lock.
if (*((volatile int *)&parser->initialized)) {
assert(parser->kwtuple != NULL);
PyThread_release_lock(_PyRuntime.getargs.mutex);
return 1;
}
int ret = _parser_init(parser);
PyThread_release_lock(_PyRuntime.getargs.mutex);
return ret;
}

static void
parser_clear(struct _PyArg_Parser *parser)
{
Expand Down