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Merged
vstinner merged 1 commit into from
Nov 27, 2025
Merged

gh-127635: Use flexible array in tracemalloc #141991

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20 changes: 12 additions & 8 deletions Include/internal/pycore_tracemalloc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -30,8 +30,8 @@ struct _PyTraceMalloc_Config {
};


/* Pack the frame_t structure to reduce the memory footprint on 64-bit
architectures: 12 bytes instead of 16. */
/* Pack the tracemalloc_frame and tracemalloc_traceback structures to reduce
the memory footprint on 64-bit architectures: 12 bytes instead of 16. */
#if defined(_MSC_VER)
#pragma pack(push, 4)
#endif
Expand All @@ -46,18 +46,22 @@ tracemalloc_frame {
PyObject *filename;
unsigned int lineno;
};
#ifdef _MSC_VER
#pragma pack(pop)
#endif

struct tracemalloc_traceback {
struct
#ifdef __GNUC__
__attribute__((packed))
#endif
tracemalloc_traceback {
Py_uhash_t hash;
/* Number of frames stored */
uint16_t nframe;
/* Total number of frames the traceback had */
uint16_t total_nframe;
struct tracemalloc_frame frames[1];
struct tracemalloc_frame frames[];
};
#ifdef _MSC_VER
#pragma pack(pop)
#endif


struct _tracemalloc_runtime_state {
Expand Down Expand Up @@ -95,7 +99,7 @@ struct _tracemalloc_runtime_state {
Protected by TABLES_LOCK(). */
_Py_hashtable_t *domains;

struct tracemalloc_traceback empty_traceback;
struct tracemalloc_traceback *empty_traceback;

Py_tss_t reentrant_key;
};
Expand Down
26 changes: 18 additions & 8 deletions Python/tracemalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,7 @@ typedef struct tracemalloc_frame frame_t;
typedef struct tracemalloc_traceback traceback_t;

#define TRACEBACK_SIZE(NFRAME) \
(sizeof(traceback_t) + sizeof(frame_t) * (NFRAME - 1))
(sizeof(traceback_t) + sizeof(frame_t) * (NFRAME))

static const int MAX_NFRAME = UINT16_MAX;

Expand Down Expand Up @@ -329,8 +329,9 @@ traceback_new(void)
traceback->nframe = 0;
traceback->total_nframe = 0;
traceback_get_frames(traceback);
if (traceback->nframe == 0)
return &tracemalloc_empty_traceback;
if (traceback->nframe == 0) {
return tracemalloc_empty_traceback;
}
traceback->hash = traceback_hash(traceback);

/* intern the traceback */
Expand Down Expand Up @@ -754,12 +755,18 @@ _PyTraceMalloc_Init(void)
return _PyStatus_NO_MEMORY();
}

tracemalloc_empty_traceback.nframe = 1;
tracemalloc_empty_traceback.total_nframe = 1;
assert(tracemalloc_empty_traceback == NULL);
tracemalloc_empty_traceback = raw_malloc(TRACEBACK_SIZE(1));
if (tracemalloc_empty_traceback == NULL) {
return _PyStatus_NO_MEMORY();
}

tracemalloc_empty_traceback->nframe = 1;
tracemalloc_empty_traceback->total_nframe = 1;
/* borrowed reference */
tracemalloc_empty_traceback.frames[0].filename = &_Py_STR(anon_unknown);
tracemalloc_empty_traceback.frames[0].lineno = 0;
tracemalloc_empty_traceback.hash = traceback_hash(&tracemalloc_empty_traceback);
tracemalloc_empty_traceback->frames[0].filename = &_Py_STR(anon_unknown);
tracemalloc_empty_traceback->frames[0].lineno = 0;
tracemalloc_empty_traceback->hash = traceback_hash(tracemalloc_empty_traceback);

tracemalloc_config.initialized = TRACEMALLOC_INITIALIZED;
return _PyStatus_OK();
Expand All @@ -782,6 +789,9 @@ tracemalloc_deinit(void)
_Py_hashtable_destroy(tracemalloc_filenames);

PyThread_tss_delete(&tracemalloc_reentrant_key);

raw_free(tracemalloc_empty_traceback);
tracemalloc_empty_traceback = NULL;
}


Expand Down
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