cpython/Lib/profiling/sampling/stack_collector.py
Pablo Galindo Salgado 4279785b31
gh-140727: Restructure profiling documentation for PEP 799 (#142373)
* Add profiling module documentation structure

PEP 799 introduces a new `profiling` package that reorganizes Python's
profiling tools under a unified namespace. This commit adds the documentation
structure to match: a main entry point (profiling.rst) that helps users choose
between profilers, detailed docs for the tracing profiler (profiling-tracing.rst),
and separated pstats documentation.

The tracing profiler docs note that cProfile remains as a backward-compatible
alias, so existing code continues to work. The pstats module gets its own page
since it's used by both profiler types and deserves focused documentation.

* Add profiling.sampling documentation

The sampling profiler is new in Python 3.15 and works fundamentally differently
from the tracing profiler. It observes programs from outside by periodically
capturing stack snapshots, which means zero overhead on the profiled code. This
makes it practical for production use where you can attach to live servers.

The docs explain the key concepts (statistical vs deterministic profiling),
provide quick examples upfront, document all output formats (pstats, flamegraph,
gecko, heatmap), and cover the live TUI mode. The defaults table helps users
understand what happens without any flags.

* Wire profiling docs into the documentation tree

Add the new profiling module pages to the Debugging and Profiling toctree.
The order places the main profiling.rst entry point first, followed by the
two profiler implementations, then pstats, and finally the deprecated profile
module last.

* Convert profile.rst to deprecation stub

The pure Python profile module is deprecated in 3.15 and scheduled for removal
in 3.17. Users should migrate to profiling.tracing (or use the cProfile alias
which continues to work).

The page now focuses on helping existing users migrate: it shows the old vs new
import style, keeps the shared API reference since both modules have the same
interface, and preserves the calibration docs for anyone still using the pure
Python implementation during the transition period.

* Update CLI module references for profiling restructure

Point cProfile to profiling.tracing docs and add profiling.sampling to the
list of modules with CLI interfaces. The old profile-cli label no longer
exists after the documentation restructure.

* Update whatsnew to link to profiling module docs

Enable cross-references to the new profiling module documentation and update
the CLI examples to use the current syntax with the attach subcommand. Also
reference profiling.tracing instead of cProfile since that's the new canonical
name.
2025-12-09 12:55:04 +00:00

389 lines
15 KiB
Python

import base64
import collections
import functools
import importlib.resources
import json
import linecache
import os
from ._css_utils import get_combined_css
from .collector import Collector
from .string_table import StringTable
class StackTraceCollector(Collector):
def __init__(self, sample_interval_usec, *, skip_idle=False):
self.sample_interval_usec = sample_interval_usec
self.skip_idle = skip_idle
def collect(self, stack_frames, skip_idle=False):
if stack_frames and hasattr(stack_frames[0], "awaited_by"):
# Async-aware mode: process async task frames
for frames, thread_id, task_id in self._iter_async_frames(stack_frames):
if not frames:
continue
self.process_frames(frames, thread_id)
else:
# Sync-only mode
for frames, thread_id in self._iter_all_frames(stack_frames, skip_idle=skip_idle):
if not frames:
continue
self.process_frames(frames, thread_id)
def process_frames(self, frames, thread_id):
pass
class CollapsedStackCollector(StackTraceCollector):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.stack_counter = collections.Counter()
def process_frames(self, frames, thread_id):
call_tree = tuple(reversed(frames))
self.stack_counter[(call_tree, thread_id)] += 1
def export(self, filename):
lines = []
for (call_tree, thread_id), count in self.stack_counter.items():
parts = [f"tid:{thread_id}"]
for file, line, func in call_tree:
# This is what pstats does for "special" frames:
if file == "~" and line == 0:
part = func
else:
part = f"{os.path.basename(file)}:{func}:{line}"
parts.append(part)
stack_str = ";".join(parts)
lines.append((stack_str, count))
lines.sort(key=lambda x: (-x[1], x[0]))
with open(filename, "w") as f:
for stack, count in lines:
f.write(f"{stack} {count}\n")
print(f"Collapsed stack output written to {filename}")
class FlamegraphCollector(StackTraceCollector):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.stats = {}
self._root = {"samples": 0, "children": {}, "threads": set()}
self._total_samples = 0
self._sample_count = 0 # Track actual number of samples (not thread traces)
self._func_intern = {}
self._string_table = StringTable()
self._all_threads = set()
# Thread status statistics (similar to LiveStatsCollector)
self.thread_status_counts = {
"has_gil": 0,
"on_cpu": 0,
"gil_requested": 0,
"unknown": 0,
"total": 0,
}
self.samples_with_gc_frames = 0
# Per-thread statistics
self.per_thread_stats = {} # {thread_id: {has_gil, on_cpu, gil_requested, unknown, total, gc_samples}}
def collect(self, stack_frames, skip_idle=False):
"""Override to track thread status statistics before processing frames."""
# Increment sample count once per sample
self._sample_count += 1
# Collect both aggregate and per-thread statistics using base method
status_counts, has_gc_frame, per_thread_stats = self._collect_thread_status_stats(stack_frames)
# Merge aggregate status counts
for key in status_counts:
self.thread_status_counts[key] += status_counts[key]
# Update aggregate GC frame count
if has_gc_frame:
self.samples_with_gc_frames += 1
# Merge per-thread statistics
for thread_id, stats in per_thread_stats.items():
if thread_id not in self.per_thread_stats:
self.per_thread_stats[thread_id] = {
"has_gil": 0,
"on_cpu": 0,
"gil_requested": 0,
"unknown": 0,
"total": 0,
"gc_samples": 0,
}
for key, value in stats.items():
self.per_thread_stats[thread_id][key] += value
# Call parent collect to process frames
super().collect(stack_frames, skip_idle=skip_idle)
def set_stats(self, sample_interval_usec, duration_sec, sample_rate,
error_rate=None, missed_samples=None, mode=None):
"""Set profiling statistics to include in flamegraph data."""
self.stats = {
"sample_interval_usec": sample_interval_usec,
"duration_sec": duration_sec,
"sample_rate": sample_rate,
"error_rate": error_rate,
"missed_samples": missed_samples,
"mode": mode
}
def export(self, filename):
flamegraph_data = self._convert_to_flamegraph_format()
# Debug output with string table statistics
num_functions = len(flamegraph_data.get("children", []))
total_time = flamegraph_data.get("value", 0)
string_count = len(self._string_table)
print(
f"Flamegraph data: {num_functions} root functions, total samples: {total_time}, "
f"{string_count} unique strings"
)
if num_functions == 0:
print(
"Warning: No functions found in profiling data. Check if sampling captured any data."
)
return
html_content = self._create_flamegraph_html(flamegraph_data)
with open(filename, "w", encoding="utf-8") as f:
f.write(html_content)
print(f"Flamegraph saved to: {filename}")
@staticmethod
@functools.lru_cache(maxsize=None)
def _format_function_name(func):
filename, lineno, funcname = func
# Special frames like <GC> and <native> should not show file:line
if filename == "~" and lineno == 0:
return funcname
if len(filename) > 50:
parts = filename.split("/")
if len(parts) > 2:
filename = f".../{'/'.join(parts[-2:])}"
return f"{funcname} ({filename}:{lineno})"
def _convert_to_flamegraph_format(self):
if self._total_samples == 0:
return {
"name": self._string_table.intern("No Data"),
"value": 0,
"children": [],
"threads": [],
"strings": self._string_table.get_strings()
}
def convert_children(children, min_samples):
out = []
for func, node in children.items():
samples = node["samples"]
if samples < min_samples:
continue
# Intern all string components for maximum efficiency
filename_idx = self._string_table.intern(func[0])
funcname_idx = self._string_table.intern(func[2])
name_idx = self._string_table.intern(self._format_function_name(func))
child_entry = {
"name": name_idx,
"value": samples,
"children": [],
"filename": filename_idx,
"lineno": func[1],
"funcname": funcname_idx,
"threads": sorted(list(node.get("threads", set()))),
}
source = self._get_source_lines(func)
if source:
# Intern source lines for memory efficiency
source_indices = [self._string_table.intern(line) for line in source]
child_entry["source"] = source_indices
# Recurse
child_entry["children"] = convert_children(
node["children"], min_samples
)
out.append(child_entry)
# Sort by value (descending) then by name index for consistent ordering
out.sort(key=lambda x: (-x["value"], x["name"]))
return out
# Filter out very small functions (less than 0.1% of total samples)
total_samples = self._total_samples
min_samples = max(1, int(total_samples * 0.001))
root_children = convert_children(self._root["children"], min_samples)
if not root_children:
return {
"name": self._string_table.intern("No significant data"),
"value": 0,
"children": [],
"strings": self._string_table.get_strings()
}
# Calculate thread status percentages for display
total_threads = max(1, self.thread_status_counts["total"])
thread_stats = {
"has_gil_pct": (self.thread_status_counts["has_gil"] / total_threads) * 100,
"on_cpu_pct": (self.thread_status_counts["on_cpu"] / total_threads) * 100,
"gil_requested_pct": (self.thread_status_counts["gil_requested"] / total_threads) * 100,
"gc_pct": (self.samples_with_gc_frames / max(1, self._sample_count)) * 100,
**self.thread_status_counts
}
# Calculate per-thread statistics with percentages
per_thread_stats_with_pct = {}
total_samples_denominator = max(1, self._sample_count)
for thread_id, stats in self.per_thread_stats.items():
total = max(1, stats["total"])
per_thread_stats_with_pct[thread_id] = {
"has_gil_pct": (stats["has_gil"] / total) * 100,
"on_cpu_pct": (stats["on_cpu"] / total) * 100,
"gil_requested_pct": (stats["gil_requested"] / total) * 100,
"gc_pct": (stats["gc_samples"] / total_samples_denominator) * 100,
**stats
}
# If we only have one root child, make it the root to avoid redundant level
if len(root_children) == 1:
main_child = root_children[0]
# Update the name to indicate it's the program root
old_name = self._string_table.get_string(main_child["name"])
new_name = f"Program Root: {old_name}"
main_child["name"] = self._string_table.intern(new_name)
main_child["stats"] = {
**self.stats,
"thread_stats": thread_stats,
"per_thread_stats": per_thread_stats_with_pct
}
main_child["threads"] = sorted(list(self._all_threads))
main_child["strings"] = self._string_table.get_strings()
return main_child
return {
"name": self._string_table.intern("Program Root"),
"value": total_samples,
"children": root_children,
"stats": {
**self.stats,
"thread_stats": thread_stats,
"per_thread_stats": per_thread_stats_with_pct
},
"threads": sorted(list(self._all_threads)),
"strings": self._string_table.get_strings()
}
def process_frames(self, frames, thread_id):
# Reverse to root->leaf
call_tree = reversed(frames)
self._root["samples"] += 1
self._total_samples += 1
self._root["threads"].add(thread_id)
self._all_threads.add(thread_id)
current = self._root
for func in call_tree:
func = self._func_intern.setdefault(func, func)
children = current["children"]
node = children.get(func)
if node is None:
node = {"samples": 0, "children": {}, "threads": set()}
children[func] = node
node["samples"] += 1
node["threads"].add(thread_id)
current = node
def _get_source_lines(self, func):
filename, lineno, _ = func
try:
lines = []
start_line = max(1, lineno - 2)
end_line = lineno + 3
for line_num in range(start_line, end_line):
line = linecache.getline(filename, line_num)
if line.strip():
marker = "" if line_num == lineno else " "
lines.append(f"{marker}{line_num}: {line.rstrip()}")
return lines if lines else None
except Exception:
return None
def _create_flamegraph_html(self, data):
data_json = json.dumps(data)
template_dir = importlib.resources.files(__package__)
vendor_dir = template_dir / "_vendor"
assets_dir = template_dir / "_assets"
d3_path = vendor_dir / "d3" / "7.8.5" / "d3.min.js"
d3_flame_graph_dir = vendor_dir / "d3-flame-graph" / "4.1.3"
fg_css_path = d3_flame_graph_dir / "d3-flamegraph.css"
fg_js_path = d3_flame_graph_dir / "d3-flamegraph.min.js"
fg_tooltip_js_path = d3_flame_graph_dir / "d3-flamegraph-tooltip.min.js"
html_template = (template_dir / "_flamegraph_assets" / "flamegraph_template.html").read_text(encoding="utf-8")
css_content = get_combined_css("flamegraph")
js_content = (template_dir / "_flamegraph_assets" / "flamegraph.js").read_text(encoding="utf-8")
# Inline first-party CSS/JS
html_template = html_template.replace(
"<!-- INLINE_CSS -->", f"<style>\n{css_content}\n</style>"
)
html_template = html_template.replace(
"<!-- INLINE_JS -->", f"<script>\n{js_content}\n</script>"
)
png_path = assets_dir / "tachyon-logo.png"
b64_logo = base64.b64encode(png_path.read_bytes()).decode("ascii")
# Let CSS control size; keep markup simple
logo_html = f'<img src="data:image/png;base64,{b64_logo}" alt="Tachyon logo"/>'
html_template = html_template.replace("<!-- INLINE_LOGO -->", logo_html)
d3_js = d3_path.read_text(encoding="utf-8")
fg_css = fg_css_path.read_text(encoding="utf-8")
fg_js = fg_js_path.read_text(encoding="utf-8")
fg_tooltip_js = fg_tooltip_js_path.read_text(encoding="utf-8")
html_template = html_template.replace(
"<!-- INLINE_VENDOR_D3_JS -->",
f"<script>\n{d3_js}\n</script>",
)
html_template = html_template.replace(
"<!-- INLINE_VENDOR_FLAMEGRAPH_CSS -->",
f"<style>\n{fg_css}\n</style>",
)
html_template = html_template.replace(
"<!-- INLINE_VENDOR_FLAMEGRAPH_JS -->",
f"<script>\n{fg_js}\n</script>",
)
html_template = html_template.replace(
"<!-- INLINE_VENDOR_FLAMEGRAPH_TOOLTIP_JS -->",
f"<script>\n{fg_tooltip_js}\n</script>",
)
# Replace the placeholder with actual data
html_content = html_template.replace(
"{{FLAMEGRAPH_DATA}}", data_json
)
return html_content