cpython/Modules/_remote_debugging/binary_io_writer.c at main · python/cpython · GitHub

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/******************************************************************************

* Python Remote Debugging Module - Binary Writer Implementation

* High-performance binary file writer for profiling data with optional zstd

* streaming compression.

******************************************************************************/

#ifndef Py_BUILD_CORE_MODULE

# define Py_BUILD_CORE_MODULE

#endif

#include "binary_io.h"

#include "_remote_debugging.h"

#include "pycore_opcode_utils.h" // MAX_REAL_OPCODE

#include <math.h>

#include <string.h>

#ifdef HAVE_ZSTD

#include <zstd.h>

#endif

/* ============================================================================

* CONSTANTS FOR BINARY FORMAT SIZES

* ============================================================================ */

/* Sample header sizes */

#define SAMPLE_HEADER_MAX_SIZE 26 /* fixed + max_varint(10) + status(1) + margin */

#define MAX_VARINT_SIZE 10 /* Maximum bytes for a varint64 */

#define MAX_VARINT_SIZE_U32 5 /* Maximum bytes for a varint32 */

/* Frame buffer: depth varint (max 2 bytes for 256) + 256 frames * 5 bytes/varint + margin */

#define MAX_FRAME_BUFFER_SIZE ((MAX_STACK_DEPTH * MAX_VARINT_SIZE_U32) + MAX_VARINT_SIZE_U32 + 16)

/* RLE pending buffer (per thread): one entry is a u64 delta varint + status byte */

#define MAX_RLE_BUF_SIZE (16 * 1024)

#define MAX_RLE_ENTRY_SIZE (MAX_VARINT_SIZE + sizeof(uint8_t))

/* Helper macro: convert PyLong to int32, using default_val if conversion fails */

#define PYLONG_TO_INT32_OR_DEFAULT(obj, var, default_val) \

do { \

(var) = (int32_t)PyLong_AsLong(obj); \

if (UNLIKELY(PyErr_Occurred() != NULL)) { \

PyErr_Clear(); \

(var) = (default_val); \

} \

} while (0)

/* ============================================================================

* WRITER-SPECIFIC UTILITY HELPERS

* ============================================================================ */

/* Grow two parallel arrays together (e.g., strings and string_lengths).

* Returns 0 on success, -1 on error (sets PyErr).

* On error, original arrays are preserved (truly atomic update). */

static inline int

grow_parallel_arrays(void **array1, void **array2, size_t *capacity,

size_t elem_size1, size_t elem_size2)

{

size_t old_cap = *capacity;

if (old_cap > SIZE_MAX / 2) {

PyErr_SetString(PyExc_OverflowError, "Array capacity overflow");

return -1;

}

size_t new_cap = old_cap * 2;

if (new_cap > SIZE_MAX / elem_size1 || new_cap > SIZE_MAX / elem_size2) {

PyErr_SetString(PyExc_OverflowError, "Array allocation size overflow");

return -1;

}

size_t new_size1 = new_cap * elem_size1;

size_t new_size2 = new_cap * elem_size2;

size_t old_size1 = old_cap * elem_size1;

size_t old_size2 = old_cap * elem_size2;

/* Allocate fresh memory blocks (not realloc) to ensure atomicity.

* If either allocation fails, original arrays are completely unchanged. */

void *new_array1 = PyMem_Malloc(new_size1);

if (!new_array1) {

PyErr_NoMemory();

return -1;

}

void *new_array2 = PyMem_Malloc(new_size2);

if (!new_array2) {

/* Second allocation failed - free first and return with no state change */

PyMem_Free(new_array1);

PyErr_NoMemory();

return -1;

}

/* Both allocations succeeded - copy data and update pointers atomically */

memcpy(new_array1, *array1, old_size1);

memcpy(new_array2, *array2, old_size2);

PyMem_Free(*array1);

PyMem_Free(*array2);

*array1 = new_array1;

*array2 = new_array2;

*capacity = new_cap;

return 0;

}

/* Checked fwrite with GIL release - returns 0 on success, -1 on error (sets PyErr).

* This version releases the GIL during the write operation to allow other Python

* threads to run during potentially blocking I/O. */

static inline int

fwrite_checked_allow_threads(const void *data, size_t size, FILE *fp)

{

size_t written;

Py_BEGIN_ALLOW_THREADS

written = fwrite(data, 1, size, fp);

Py_END_ALLOW_THREADS

if (written != size) {

int err = errno;

if (ferror(fp) && err != 0) {

errno = err;

PyErr_SetFromErrno(PyExc_IOError);

}

else {

PyErr_Format(PyExc_IOError,

"short write: wrote %zu of %zu bytes", written, size);

}

return -1;

}

return 0;

}

/* Forward declaration for writer_write_bytes */

static inline int writer_write_bytes(BinaryWriter *writer, const void *data, size_t size);

/* Encode and write a varint u32 - returns 0 on success, -1 on error */

static inline int

writer_write_varint_u32(BinaryWriter *writer, uint32_t value)

{

uint8_t buf[MAX_VARINT_SIZE];

size_t len = encode_varint_u32(buf, value);

return writer_write_bytes(writer, buf, len);

}

/* ============================================================================

* UTILITY FUNCTIONS

* ============================================================================ */

int

binary_io_zstd_available(void)

{

#ifdef HAVE_ZSTD

return 1;

#else

return 0;

#endif

}

int

binary_io_get_best_compression(void)

{

#ifdef HAVE_ZSTD

return COMPRESSION_ZSTD;

#else

return COMPRESSION_NONE;

#endif

}

/* ============================================================================

* BINARY WRITER IMPLEMENTATION

* ============================================================================ */

static int

writer_init_zstd(BinaryWriter *writer)

{

#ifdef HAVE_ZSTD

writer->zstd.cctx = ZSTD_createCCtx();

if (!writer->zstd.cctx) {

PyErr_SetString(PyExc_MemoryError, "Failed to create zstd compression context");

return -1;

}

/* Compression level 5: better ratio for repetitive profiling data */

size_t result = ZSTD_CCtx_setParameter(writer->zstd.cctx,

ZSTD_c_compressionLevel, 5);

if (ZSTD_isError(result)) {

PyErr_Format(PyExc_RuntimeError, "Failed to set zstd compression level: %s",

ZSTD_getErrorName(result));

ZSTD_freeCCtx(writer->zstd.cctx);

writer->zstd.cctx = NULL;

return -1;

}

/* Use large buffer (512KB) for fewer I/O syscalls */

writer->zstd.compressed_buffer = PyMem_Malloc(COMPRESSED_BUFFER_SIZE);

if (!writer->zstd.compressed_buffer) {

ZSTD_freeCCtx(writer->zstd.cctx);

writer->zstd.cctx = NULL;

PyErr_NoMemory();

return -1;

}

writer->zstd.compressed_buffer_size = COMPRESSED_BUFFER_SIZE;

return 0;

#else

PyErr_SetString(PyExc_RuntimeError,

"zstd compression requested but not available (HAVE_ZSTD not defined)");

return -1;

#endif

}

static int

writer_flush_buffer(BinaryWriter *writer)

{

if (writer->buffer_pos == 0) {

return 0;

}

#ifdef HAVE_ZSTD

if (writer->compression_type == COMPRESSION_ZSTD) {

ZSTD_inBuffer input = { writer->write_buffer, writer->buffer_pos, 0 };

while (input.pos < input.size) {

ZSTD_outBuffer output = {

writer->zstd.compressed_buffer,

writer->zstd.compressed_buffer_size,

};

size_t result = ZSTD_compressStream2(

writer->zstd.cctx, &output, &input, ZSTD_e_continue

);

if (ZSTD_isError(result)) {

PyErr_Format(PyExc_IOError, "zstd compression error: %s",

ZSTD_getErrorName(result));

return -1;

}

if (output.pos > 0) {

if (fwrite_checked_allow_threads(writer->zstd.compressed_buffer, output.pos, writer->fp) < 0) {

return -1;

}

} else

#endif

{

if (fwrite_checked_allow_threads(writer->write_buffer, writer->buffer_pos, writer->fp) < 0) {

return -1;

}

writer->buffer_pos = 0;

return 0;

}

static inline int

writer_write_bytes(BinaryWriter *writer, const void *data, size_t size)

{

const uint8_t *src = (const uint8_t *)data;

size_t original_size = size;

while (size > 0) {

size_t space = writer->buffer_size - writer->buffer_pos;

size_t to_copy = (size < space) ? size : space;

memcpy(writer->write_buffer + writer->buffer_pos, src, to_copy);

writer->buffer_pos += to_copy;

src += to_copy;

size -= to_copy;

if (writer->buffer_pos == writer->buffer_size) {

if (writer_flush_buffer(writer) < 0) {

return -1;

}

writer->stats.bytes_written += original_size;

return 0;

}

/* ============================================================================

* HASH TABLE SUPPORT FUNCTIONS (using _Py_hashtable)

* ============================================================================ */

/* Hash function for Python strings - uses Python's cached hash */

static Py_uhash_t

string_hash_func(const void *key)

{

PyObject *str = (PyObject *)key;

Py_hash_t hash = PyObject_Hash(str);

if (hash == -1) {

PyErr_Clear();

return 0;

}

return (Py_uhash_t)hash;

}

static int

string_compare_func(const void *key1, const void *key2)

{

PyObject *str1 = (PyObject *)key1;

PyObject *str2 = (PyObject *)key2;

if (str1 == str2) {

return 1;

}

int result = PyObject_RichCompareBool(str1, str2, Py_EQ);

if (result == -1) {

PyErr_Clear();

return 0;

}

return result;

}

static void

string_key_destroy(void *key)

{

Py_XDECREF((PyObject *)key);

}

static Py_uhash_t

frame_key_hash_func(const void *key)

{

const FrameKey *fk = (const FrameKey *)key;

/* FNV-1a style hash combining all fields */

Py_uhash_t hash = 2166136261u;

hash ^= fk->filename_idx;

hash *= 16777619u;

hash ^= fk->funcname_idx;

hash *= 16777619u;

hash ^= (uint32_t)fk->lineno;

hash *= 16777619u;

hash ^= (uint32_t)fk->end_lineno;

hash *= 16777619u;

hash ^= (uint32_t)fk->column;

hash *= 16777619u;

hash ^= (uint32_t)fk->end_column;

hash *= 16777619u;

hash ^= fk->opcode;

hash *= 16777619u;

return hash;

}

static int

frame_key_compare_func(const void *key1, const void *key2)

{

const FrameKey *fk1 = (const FrameKey *)key1;

const FrameKey *fk2 = (const FrameKey *)key2;

return (fk1->filename_idx == fk2->filename_idx &&

fk1->funcname_idx == fk2->funcname_idx &&

fk1->lineno == fk2->lineno &&

fk1->end_lineno == fk2->end_lineno &&

fk1->column == fk2->column &&

fk1->end_column == fk2->end_column &&

fk1->opcode == fk2->opcode);

}

static void

frame_key_destroy(void *key)

{

PyMem_Free(key);

}

static inline int

writer_intern_string(BinaryWriter *writer, PyObject *string, uint32_t *index)

{

void *existing = _Py_hashtable_get(writer->string_hash, string);

if (existing != NULL) {

*index = (uint32_t)(uintptr_t)existing - 1; /* index+1 stored to distinguish from NULL */

return 0;

}

if (writer->string_count >= UINT32_MAX) {

PyErr_SetString(PyExc_OverflowError,

"too many strings for binary format");

return -1;

}

if (writer->string_count >= writer->string_capacity) {

if (grow_parallel_arrays((void **)&writer->strings,

(void **)&writer->string_lengths,

&writer->string_capacity,

sizeof(char *), sizeof(size_t)) < 0) {

return -1;

}

Py_ssize_t str_len;

const char *str_data = PyUnicode_AsUTF8AndSize(string, &str_len);

if (!str_data) {

return -1;

}

if ((uintmax_t)str_len > UINT32_MAX) {

PyErr_Format(PyExc_OverflowError,

"string length %zd exceeds binary format maximum %u",

str_len, UINT32_MAX);

return -1;

}

char *str_copy = PyMem_Malloc(str_len + 1);

if (!str_copy) {

PyErr_NoMemory();

return -1;

}

memcpy(str_copy, str_data, str_len + 1);

*index = (uint32_t)writer->string_count;

/* Add to hash table FIRST to ensure atomic rollback on failure */

Py_INCREF(string);

if (_Py_hashtable_set(writer->string_hash, string, (void *)(uintptr_t)(*index + 1)) < 0) {

Py_DECREF(string);

PyMem_Free(str_copy);

PyErr_NoMemory();

return -1;

}

writer->strings[writer->string_count] = str_copy;

writer->string_lengths[writer->string_count] = str_len;

writer->string_count++;

return 0;

}

static inline int

writer_intern_frame(BinaryWriter *writer, const FrameEntry *entry, uint32_t *index)

{

FrameKey lookup_key = {

entry->filename_idx, entry->funcname_idx,

entry->lineno, entry->end_lineno,

entry->column, entry->end_column,

entry->opcode

};

void *existing = _Py_hashtable_get(writer->frame_hash, &lookup_key);

if (existing != NULL) {

*index = (uint32_t)(uintptr_t)existing - 1; /* index+1 stored to distinguish from NULL */

return 0;

}

if (writer->frame_count >= UINT32_MAX) {

PyErr_SetString(PyExc_OverflowError,

"too many frames for binary format");

return -1;

}

if (GROW_ARRAY(writer->frame_entries, writer->frame_count,

writer->frame_capacity, FrameEntry) < 0) {

return -1;

}

FrameKey *key = PyMem_Malloc(sizeof(FrameKey));

if (!key) {

PyErr_NoMemory();

return -1;

}

*key = lookup_key;

*index = (uint32_t)writer->frame_count;

writer->frame_entries[writer->frame_count] = *entry;

if (_Py_hashtable_set(writer->frame_hash, key, (void *)(uintptr_t)(*index + 1)) < 0) {

PyMem_Free(key);

PyErr_NoMemory();

return -1;

}

writer->frame_count++;

return 0;

}

/* Get or create a thread entry for the given thread_id.

* Returns pointer to ThreadEntry, or NULL on allocation failure.

* If is_new is non-NULL, sets it to 1 if this is a new thread, 0 otherwise. */

static ThreadEntry *

writer_get_or_create_thread_entry(BinaryWriter *writer, uint64_t thread_id,

uint32_t interpreter_id, int *is_new)

{

/* Linear search is OK for small number of threads.

* Key is (thread_id, interpreter_id) since same thread_id can exist in different interpreters. */

for (size_t i = 0; i < writer->thread_count; i++) {

if (writer->thread_entries[i].thread_id == thread_id &&

writer->thread_entries[i].interpreter_id == interpreter_id) {

if (is_new) {

*is_new = 0;

}

return &writer->thread_entries[i];

}

if (writer->thread_count >= UINT32_MAX) {

PyErr_SetString(PyExc_OverflowError,

"too many threads for binary format");

return NULL;

}

if (writer->thread_count >= writer->thread_capacity) {

ThreadEntry *new_entries = grow_array(writer->thread_entries,

&writer->thread_capacity,

sizeof(ThreadEntry));

if (!new_entries) {

return NULL;

}

writer->thread_entries = new_entries;

}

ThreadEntry *entry = &writer->thread_entries[writer->thread_count];

memset(entry, 0, sizeof(ThreadEntry));

entry->thread_id = thread_id;

entry->interpreter_id = interpreter_id;

entry->prev_timestamp = writer->start_time_us;

entry->prev_stack_capacity = MAX_STACK_DEPTH;

entry->prev_stack = PyMem_Calloc(entry->prev_stack_capacity, sizeof(uint32_t));

if (!entry->prev_stack) {

PyErr_NoMemory();

return NULL;

}

writer->thread_count++;

if (is_new) {

*is_new = 1;

}

return entry;

}

/* Compare two stacks and return the encoding type and parameters.

* Sets:

* - shared_count: number of frames matching from bottom of stack

* - pop_count: frames to remove from prev stack

* - push_count: new frames to add

* Returns the best encoding type to use. */

static int

compare_stacks(const uint32_t *prev_stack, size_t prev_depth,

const uint32_t *curr_stack, size_t curr_depth,

size_t *shared_count, size_t *pop_count, size_t *push_count)

{

if (prev_depth == curr_depth) {

int identical = 1;

for (size_t i = 0; i < prev_depth; i++) {

if (prev_stack[i] != curr_stack[i]) {

identical = 0;

break;

}

if (identical) {

*shared_count = prev_depth;

*pop_count = 0;

*push_count = 0;

return STACK_REPEAT;

}

/* Find longest common suffix (frames at the bottom/outer part of stack).

* Stacks are stored innermost-first, so suffix is at the end. */

size_t suffix_len = 0;

size_t min_depth = (prev_depth < curr_depth) ? prev_depth : curr_depth;

for (size_t i = 0; i < min_depth; i++) {

size_t prev_idx = prev_depth - 1 - i;

size_t curr_idx = curr_depth - 1 - i;

if (prev_stack[prev_idx] == curr_stack[curr_idx]) {

suffix_len++;

} else {

break;

}

*shared_count = suffix_len;

*pop_count = prev_depth - suffix_len;

*push_count = curr_depth - suffix_len;

/* Choose best encoding based on byte cost */

/* STACK_FULL: 1 (type) + 1-2 (depth) + sum(frame varints) */

/* STACK_SUFFIX: 1 (type) + 1-2 (shared) + 1-2 (new_count) + sum(new frame varints) */

/* STACK_POP_PUSH: 1 (type) + 1-2 (pop) + 1-2 (push) + sum(new frame varints) */

/* If no common suffix, use full stack */

if (suffix_len == 0) {

return STACK_FULL;

}

/* If only adding frames (suffix == prev_depth), use SUFFIX */

if (*pop_count == 0 && *push_count > 0) {

return STACK_SUFFIX;

}

/* If popping and/or pushing, use POP_PUSH if it saves bytes */

/* Heuristic: POP_PUSH is better when we're modifying top frames */

if (*pop_count > 0 || *push_count > 0) {

/* Use full stack if sharing less than half the frames */

if (suffix_len < curr_depth / 2) {

return STACK_FULL;

}

return STACK_POP_PUSH;

}

return STACK_FULL;

}

/* Write common sample header: thread_id(8) + interpreter_id(4) + encoding(1).

* Returns 0 on success, -1 on failure. */

static inline int

write_sample_header(BinaryWriter *writer, ThreadEntry *entry, uint8_t encoding)

{

uint8_t header[SAMPLE_HEADER_FIXED_SIZE];

memcpy(header + SMP_OFF_THREAD_ID, &entry->thread_id, SMP_SIZE_THREAD_ID);

memcpy(header + SMP_OFF_INTERPRETER_ID, &entry->interpreter_id, SMP_SIZE_INTERPRETER_ID);

header[SMP_OFF_ENCODING] = encoding;

return writer_write_bytes(writer, header, SAMPLE_HEADER_FIXED_SIZE);

}

/* Flush pending RLE samples for a thread.

* Writes the RLE record to the output buffer.

* Returns 0 on success, -1 on failure. */

static int

flush_pending_rle(BinaryWriter *writer, ThreadEntry *entry)

{

if (entry->pending_rle_samples == 0) {

return 0;

}

/* Write RLE record:

* [thread_id: 8] [interpreter_id: 4] [STACK_REPEAT: 1] [count: varint]

* [timestamp_delta_1: varint] [status_1: 1] ... [timestamp_delta_N: varint] [status_N: 1]

if (write_sample_header(writer, entry, STACK_REPEAT) < 0) {

return -1;

}

if (writer_write_varint_u32(writer, (uint32_t)entry->pending_rle_samples) < 0) {

return -1;

}

if (writer_write_bytes(writer, entry->pending_rle, entry->pending_rle_bytes) < 0) {

return -1;

}

writer->stats.repeat_records++;

writer->stats.repeat_samples += entry->pending_rle_samples;

/* Each RLE sample saves writing the entire stack */

writer->stats.frames_saved += entry->pending_rle_samples * entry->prev_stack_depth;

entry->pending_rle_bytes = 0;

entry->pending_rle_samples = 0;

return 0;

}

/* Write a single sample with the specified encoding.

* Returns 0 on success, -1 on failure. */

static int

write_sample_with_encoding(BinaryWriter *writer, ThreadEntry *entry,

uint64_t timestamp_delta, uint8_t status,

int encoding_type,

const uint32_t *frame_indices, size_t stack_depth,

size_t shared_count, size_t pop_count, size_t push_count)

{

/* Header: thread_id(8) + interpreter_id(4) + encoding(1) + delta(varint) + status(1) */

uint8_t header_buf[SAMPLE_HEADER_MAX_SIZE];

memcpy(header_buf + SMP_OFF_THREAD_ID, &entry->thread_id, SMP_SIZE_THREAD_ID);

memcpy(header_buf + SMP_OFF_INTERPRETER_ID, &entry->interpreter_id, SMP_SIZE_INTERPRETER_ID);

header_buf[SMP_OFF_ENCODING] = (uint8_t)encoding_type;

size_t varint_len = encode_varint_u64(

header_buf + SAMPLE_HEADER_FIXED_SIZE,

timestamp_delta);

header_buf[SAMPLE_HEADER_FIXED_SIZE + varint_len] = status;

if (writer_write_bytes(writer, header_buf,

SAMPLE_HEADER_FIXED_SIZE + varint_len + 1) < 0) {

return -1;

}

uint8_t frame_buf[MAX_FRAME_BUFFER_SIZE];

size_t frame_buf_pos = 0;

size_t frames_written = 0;

switch (encoding_type) {

case STACK_FULL:

/* [depth: varint] [frame_idx: varint]... */

frame_buf_pos += encode_varint_u32(frame_buf, (uint32_t)stack_depth);

for (size_t i = 0; i < stack_depth; i++) {

frame_buf_pos += encode_varint_u32(frame_buf + frame_buf_pos, frame_indices[i]);

}

frames_written = stack_depth;

writer->stats.full_records++;

break;

case STACK_SUFFIX:

/* [shared_count: varint] [new_count: varint] [new_frame_idx: varint]... */

frame_buf_pos += encode_varint_u32(frame_buf, (uint32_t)shared_count);

frame_buf_pos += encode_varint_u32(frame_buf + frame_buf_pos, (uint32_t)push_count);

/* New frames are at the top (beginning) of current stack */

for (size_t i = 0; i < push_count; i++) {

frame_buf_pos += encode_varint_u32(frame_buf + frame_buf_pos, frame_indices[i]);

}

frames_written = push_count;

writer->stats.suffix_records++;

/* Saved writing shared_count frames */

writer->stats.frames_saved += shared_count;

break;

case STACK_POP_PUSH:

/* [pop_count: varint] [push_count: varint] [new_frame_idx: varint]... */

frame_buf_pos += encode_varint_u32(frame_buf, (uint32_t)pop_count);

frame_buf_pos += encode_varint_u32(frame_buf + frame_buf_pos, (uint32_t)push_count);

/* New frames are at the top (beginning) of current stack */

for (size_t i = 0; i < push_count; i++) {

frame_buf_pos += encode_varint_u32(frame_buf + frame_buf_pos, frame_indices[i]);

}

frames_written = push_count;

writer->stats.pop_push_records++;

/* Saved writing shared_count frames (stack_depth - push_count if we had written full) */

writer->stats.frames_saved += shared_count;

break;

default:

PyErr_SetString(PyExc_RuntimeError, "Invalid stack encoding type");

return -1;

}

if (writer_write_bytes(writer, frame_buf, frame_buf_pos) < 0) {

return -1;

}

writer->stats.total_frames_written += frames_written;

return 0;

}

BinaryWriter *

binary_writer_create(PyObject *path, uint64_t sample_interval_us, int compression_type,

uint64_t start_time_us)

{

BinaryWriter *writer = PyMem_Calloc(1, sizeof(BinaryWriter));

if (!writer) {

PyErr_NoMemory();

return NULL;

}

writer->start_time_us = start_time_us;

writer->sample_interval_us = sample_interval_us;

writer->compression_type = compression_type;

writer->write_buffer = PyMem_Malloc(WRITE_BUFFER_SIZE);

if (!writer->write_buffer) {

PyErr_NoMemory();

goto error;

}

writer->buffer_size = WRITE_BUFFER_SIZE;

writer->string_hash = _Py_hashtable_new_full(

string_hash_func,

string_compare_func,

string_key_destroy, /* Key destroy: decref the Python string */

NULL, /* Value destroy: values are just indices, not pointers */

NULL /* Use default allocator */

);

if (!writer->string_hash) {

PyErr_NoMemory();

goto error;

}

writer->strings = PyMem_Malloc(INITIAL_STRING_CAPACITY * sizeof(char *));

if (!writer->strings) {

PyErr_NoMemory();

goto error;

}

writer->string_lengths = PyMem_Malloc(INITIAL_STRING_CAPACITY * sizeof(size_t));

if (!writer->string_lengths) {

PyErr_NoMemory();

goto error;

}

writer->string_capacity = INITIAL_STRING_CAPACITY;

writer->frame_hash = _Py_hashtable_new_full(

frame_key_hash_func,

frame_key_compare_func,

frame_key_destroy, /* Key destroy: free the FrameKey */

NULL, /* Value destroy: values are just indices, not pointers */

NULL /* Use default allocator */

);

if (!writer->frame_hash) {

PyErr_NoMemory();

goto error;

}

writer->frame_entries = PyMem_Malloc(INITIAL_FRAME_CAPACITY * sizeof(FrameEntry));

if (!writer->frame_entries) {

PyErr_NoMemory();

goto error;

}

writer->frame_capacity = INITIAL_FRAME_CAPACITY;

writer->thread_entries = PyMem_Malloc(INITIAL_THREAD_CAPACITY * sizeof(ThreadEntry));

if (!writer->thread_entries) {

PyErr_NoMemory();

goto error;

}

writer->thread_capacity = INITIAL_THREAD_CAPACITY;

if (compression_type == COMPRESSION_ZSTD) {

if (writer_init_zstd(writer) < 0) {

goto error;

}

writer->fp = Py_fopen(path, "wb");

if (!writer->fp) {

goto error;

}

/* Hint sequential write pattern to kernel for better I/O scheduling */

#if defined(__linux__) && defined(POSIX_FADV_SEQUENTIAL)

{

int fd = fileno(writer->fp);

if (fd >= 0) {

(void)posix_fadvise(fd, 0, 0, POSIX_FADV_SEQUENTIAL);

}

#endif

uint8_t header[FILE_HEADER_PLACEHOLDER_SIZE] = {0};

if (fwrite_checked_allow_threads(header, FILE_HEADER_PLACEHOLDER_SIZE, writer->fp) < 0) {

goto error;

}

return writer;

error:

binary_writer_destroy(writer);

return NULL;

}

/* Build a frame stack from Python frame list by interning all strings and frames.

* Returns 0 on success, -1 on error. */

static int

build_frame_stack(BinaryWriter *writer, PyObject *frame_list,

uint32_t *curr_stack, size_t *curr_depth)

{

Py_ssize_t stack_depth = PyList_Size(frame_list);

*curr_depth = (stack_depth < MAX_STACK_DEPTH) ? stack_depth : MAX_STACK_DEPTH;

for (Py_ssize_t k = 0; k < (Py_ssize_t)*curr_depth; k++) {

/* Use unchecked accessors since we control the data structures */

PyObject *frame_info = PyList_GET_ITEM(frame_list, k);

/* Get filename, location, funcname, opcode from FrameInfo using unchecked access */

PyObject *filename = PyStructSequence_GET_ITEM(frame_info, 0);

PyObject *location = PyStructSequence_GET_ITEM(frame_info, 1);

PyObject *funcname = PyStructSequence_GET_ITEM(frame_info, 2);

PyObject *opcode_obj = PyStructSequence_GET_ITEM(frame_info, 3);

/* Extract location fields (can be None for synthetic frames) */

int32_t lineno = LOCATION_NOT_AVAILABLE;

int32_t end_lineno = LOCATION_NOT_AVAILABLE;

int32_t column = LOCATION_NOT_AVAILABLE;

int32_t end_column = LOCATION_NOT_AVAILABLE;

if (location != Py_None) {

/* LocationInfo is a struct sequence or tuple with:

* (lineno, end_lineno, column, end_column) */

PyObject *lineno_obj = PyTuple_Check(location) ?

PyTuple_GET_ITEM(location, 0) :

PyStructSequence_GET_ITEM(location, 0);

PyObject *end_lineno_obj = PyTuple_Check(location) ?

PyTuple_GET_ITEM(location, 1) :

PyStructSequence_GET_ITEM(location, 1);

PyObject *column_obj = PyTuple_Check(location) ?

PyTuple_GET_ITEM(location, 2) :

PyStructSequence_GET_ITEM(location, 2);

PyObject *end_column_obj = PyTuple_Check(location) ?

PyTuple_GET_ITEM(location, 3) :

PyStructSequence_GET_ITEM(location, 3);

PYLONG_TO_INT32_OR_DEFAULT(lineno_obj, lineno, LOCATION_NOT_AVAILABLE);

PYLONG_TO_INT32_OR_DEFAULT(end_lineno_obj, end_lineno, LOCATION_NOT_AVAILABLE);

PYLONG_TO_INT32_OR_DEFAULT(column_obj, column, LOCATION_NOT_AVAILABLE);

PYLONG_TO_INT32_OR_DEFAULT(end_column_obj, end_column, LOCATION_NOT_AVAILABLE);

}

/* Extract opcode (can be None) */

uint8_t opcode = OPCODE_NONE;

if (opcode_obj != Py_None) {

long opcode_long = PyLong_AsLong(opcode_obj);

if (UNLIKELY(PyErr_Occurred() != NULL)) {

PyErr_Clear();

opcode = OPCODE_NONE;

} else if (opcode_long >= 0 && opcode_long <= MAX_REAL_OPCODE) {

opcode = (uint8_t)opcode_long;

}

/* Intern filename */

uint32_t filename_idx;

if (writer_intern_string(writer, filename, &filename_idx) < 0) {

return -1;

}

/* Intern funcname */

uint32_t funcname_idx;

if (writer_intern_string(writer, funcname, &funcname_idx) < 0) {

return -1;

}

/* Intern frame with full location info */

FrameEntry frame_entry = {

.filename_idx = filename_idx,

.funcname_idx = funcname_idx,

.lineno = lineno,

.end_lineno = end_lineno,

.column = column,

.end_column = end_column,

.opcode = opcode

};

uint32_t frame_idx;

if (writer_intern_frame(writer, &frame_entry, &frame_idx) < 0) {

return -1;

}

curr_stack[k] = frame_idx;

}

return 0;

}

/* Process a single thread's sample.

* Returns 0 on success, -1 on error. */

static int

process_thread_sample(BinaryWriter *writer, PyObject *thread_info,

uint32_t interpreter_id, uint64_t timestamp_us)

{

PyObject *thread_id_obj = PyStructSequence_GET_ITEM(thread_info, 0);

PyObject *status_obj = PyStructSequence_GET_ITEM(thread_info, 1);

PyObject *frame_list = PyStructSequence_GET_ITEM(thread_info, 2);

uint64_t thread_id = PyLong_AsUnsignedLongLong(thread_id_obj);

if (thread_id == (uint64_t)-1 && PyErr_Occurred()) {

return -1;

}

long status_long = PyLong_AsLong(status_obj);

if (status_long == -1 && PyErr_Occurred()) {

return -1;

}

uint8_t status = (uint8_t)status_long;

ThreadEntry *entry = writer_get_or_create_thread_entry(

writer, thread_id, interpreter_id, NULL);

if (!entry) {

return -1;

}

/* Calculate timestamp delta */

uint64_t delta = timestamp_us - entry->prev_timestamp;

entry->prev_timestamp = timestamp_us;

/* Process frames and build current stack */

uint32_t curr_stack[MAX_STACK_DEPTH];

size_t curr_depth;

if (build_frame_stack(writer, frame_list, curr_stack, &curr_depth) < 0) {

return -1;

}

/* Compare with previous stack to determine encoding */

size_t shared_count, pop_count, push_count;

int encoding = compare_stacks(

entry->prev_stack, entry->prev_stack_depth,

curr_stack, curr_depth,

&shared_count, &pop_count, &push_count);

if (encoding == STACK_REPEAT) {

/* Buffer this sample for RLE.

* STACK_REPEAT also covers the "first sample for a fresh thread,

* empty stack" case: a new ThreadEntry has prev_stack_depth == 0

* and a zero-initialized prev_stack, so compare_stacks() returns

* STACK_REPEAT against an empty curr_stack (depth 0). Buffering

* it here is correct; the RLE flush path emits it as a normal

* STACK_REPEAT record. */

if (entry->pending_rle == NULL) {

entry->pending_rle = PyMem_Malloc(MAX_RLE_BUF_SIZE);

if (!entry->pending_rle) {

PyErr_NoMemory();

return -1;

}

if (entry->pending_rle_bytes + MAX_RLE_ENTRY_SIZE > MAX_RLE_BUF_SIZE

&& flush_pending_rle(writer, entry) < 0) {

return -1;

}

entry->pending_rle_bytes += encode_varint_u64(

entry->pending_rle + entry->pending_rle_bytes, delta);

entry->pending_rle[entry->pending_rle_bytes++] = status;

entry->pending_rle_samples++;

} else {

/* Stack changed - flush any pending RLE first */

if (flush_pending_rle(writer, entry) < 0) {

return -1;

}

if (write_sample_with_encoding(writer, entry, delta, status, encoding,

curr_stack, curr_depth,

shared_count, pop_count, push_count) < 0) {

return -1;

}

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