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Oct 15, 2025
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gh-140137: Handle empty collections in profiling.sampling #140154

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160b9f8
gh-140137: Handle empty collections in profiling.sampling
pablogsal Oct 15, 2025
d8f6806
fixup! gh-140137: Handle empty collections in profiling.sampling
pablogsal Oct 15, 2025
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11 changes: 8 additions & 3 deletions Lib/profiling/sampling/sample.py
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Original file line number Diff line number Diff line change
Expand Up @@ -642,9 +642,14 @@ def sample(

if output_format == "pstats" and not filename:
stats = pstats.SampledStats(collector).strip_dirs()
print_sampled_stats(
stats, sort, limit, show_summary, sample_interval_usec
)
if not stats.stats:
print("No samples were collected.")
if mode == PROFILING_MODE_CPU:
print("This can happen in CPU mode when all threads are idle.")
else:
print_sampled_stats(
stats, sort, limit, show_summary, sample_interval_usec
)
else:
collector.export(filename)

Expand Down
1 change: 1 addition & 0 deletions Lib/pstats.py
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,7 @@ def load_stats(self, arg):
arg.create_stats()
self.stats = arg.stats
arg.stats = {}
return
if not self.stats:
raise TypeError("Cannot create or construct a %r object from %r"
% (self.__class__, arg))
Expand Down
118 changes: 88 additions & 30 deletions Lib/test/test_profiling/test_sampling_profiler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
import sys
import tempfile
import unittest
from collections import namedtuple
from unittest import mock

from profiling.sampling.pstats_collector import PstatsCollector
Expand Down Expand Up @@ -84,6 +85,8 @@ def __repr__(self):
"Test only runs on Linux, Windows and MacOS",
)

SubprocessInfo = namedtuple('SubprocessInfo', ['process', 'socket'])


@contextlib.contextmanager
def test_subprocess(script):
Expand Down Expand Up @@ -123,7 +126,7 @@ def test_subprocess(script):
if response != b"ready":
raise RuntimeError(f"Unexpected response from subprocess: {response}")

yield proc
yield SubprocessInfo(proc, client_socket)
finally:
if client_socket is not None:
client_socket.close()
Expand Down Expand Up @@ -1752,13 +1755,13 @@ def main_loop():

def test_sampling_basic_functionality(self):
with (
test_subprocess(self.test_script) as proc,
test_subprocess(self.test_script) as subproc,
io.StringIO() as captured_output,
mock.patch("sys.stdout", captured_output),
):
try:
profiling.sampling.sample.sample(
proc.pid,
subproc.process.pid,
duration_sec=2,
sample_interval_usec=1000, # 1ms
show_summary=False,
Expand All @@ -1782,15 +1785,15 @@ def test_sampling_with_pstats_export(self):
)
self.addCleanup(close_and_unlink, pstats_out)

with test_subprocess(self.test_script) as proc:
with test_subprocess(self.test_script) as subproc:
# Suppress profiler output when testing file export
with (
io.StringIO() as captured_output,
mock.patch("sys.stdout", captured_output),
):
try:
profiling.sampling.sample.sample(
proc.pid,
subproc.process.pid,
duration_sec=1,
filename=pstats_out.name,
sample_interval_usec=10000,
Expand Down Expand Up @@ -1826,7 +1829,7 @@ def test_sampling_with_collapsed_export(self):
self.addCleanup(close_and_unlink, collapsed_file)

with (
test_subprocess(self.test_script) as proc,
test_subprocess(self.test_script) as subproc,
):
# Suppress profiler output when testing file export
with (
Expand All @@ -1835,7 +1838,7 @@ def test_sampling_with_collapsed_export(self):
):
try:
profiling.sampling.sample.sample(
proc.pid,
subproc.process.pid,
duration_sec=1,
filename=collapsed_file.name,
output_format="collapsed",
Expand Down Expand Up @@ -1876,14 +1879,14 @@ def test_sampling_with_collapsed_export(self):

def test_sampling_all_threads(self):
with (
test_subprocess(self.test_script) as proc,
test_subprocess(self.test_script) as subproc,
# Suppress profiler output
io.StringIO() as captured_output,
mock.patch("sys.stdout", captured_output),
):
try:
profiling.sampling.sample.sample(
proc.pid,
subproc.process.pid,
duration_sec=1,
all_threads=True,
sample_interval_usec=10000,
Expand Down Expand Up @@ -1969,14 +1972,14 @@ def test_invalid_pid(self):
profiling.sampling.sample.sample(-1, duration_sec=1)

def test_process_dies_during_sampling(self):
with test_subprocess("import time; time.sleep(0.5); exit()") as proc:
with test_subprocess("import time; time.sleep(0.5); exit()") as subproc:
with (
io.StringIO() as captured_output,
mock.patch("sys.stdout", captured_output),
):
try:
profiling.sampling.sample.sample(
proc.pid,
subproc.process.pid,
duration_sec=2, # Longer than process lifetime
sample_interval_usec=50000,
)
Expand Down Expand Up @@ -2018,17 +2021,17 @@ def test_invalid_output_format_with_mocked_profiler(self):
)

def test_is_process_running(self):
with test_subprocess("import time; time.sleep(1000)") as proc:
with test_subprocess("import time; time.sleep(1000)") as subproc:
try:
profiler = SampleProfiler(pid=proc.pid, sample_interval_usec=1000, all_threads=False)
profiler = SampleProfiler(pid=subproc.process.pid, sample_interval_usec=1000, all_threads=False)
except PermissionError:
self.skipTest(
"Insufficient permissions to read the stack trace"
)
self.assertTrue(profiler._is_process_running())
self.assertIsNotNone(profiler.unwinder.get_stack_trace())
proc.kill()
proc.wait()
subproc.process.kill()
subproc.process.wait()
self.assertRaises(ProcessLookupError, profiler.unwinder.get_stack_trace)

# Exit the context manager to ensure the process is terminated
Expand All @@ -2037,20 +2040,20 @@ def test_is_process_running(self):

@unittest.skipUnless(sys.platform == "linux", "Only valid on Linux")
def test_esrch_signal_handling(self):
with test_subprocess("import time; time.sleep(1000)") as proc:
with test_subprocess("import time; time.sleep(1000)") as subproc:
try:
unwinder = _remote_debugging.RemoteUnwinder(proc.pid)
unwinder = _remote_debugging.RemoteUnwinder(subproc.process.pid)
except PermissionError:
self.skipTest(
"Insufficient permissions to read the stack trace"
)
initial_trace = unwinder.get_stack_trace()
self.assertIsNotNone(initial_trace)

proc.kill()
subproc.process.kill()

# Wait for the process to die and try to get another trace
proc.wait()
subproc.process.wait()

with self.assertRaises(ProcessLookupError):
unwinder.get_stack_trace()
Expand Down Expand Up @@ -2644,35 +2647,47 @@ def test_cpu_mode_integration_filtering(self):
import time
import threading

cpu_ready = threading.Event()

def idle_worker():
time.sleep(999999)

def cpu_active_worker():
cpu_ready.set()
x = 1
while True:
x += 1

def main():
# Start both threads
# Start both threads
idle_thread = threading.Thread(target=idle_worker)
cpu_thread = threading.Thread(target=cpu_active_worker)
idle_thread.start()
cpu_thread.start()

# Wait for CPU thread to be running, then signal test
cpu_ready.wait()
_test_sock.sendall(b"threads_ready")

idle_thread.join()
cpu_thread.join()

main()

'''
with test_subprocess(cpu_vs_idle_script) as proc:
with test_subprocess(cpu_vs_idle_script) as subproc:
# Wait for signal that threads are running
response = subproc.socket.recv(1024)
self.assertEqual(response, b"threads_ready")

with (
io.StringIO() as captured_output,
mock.patch("sys.stdout", captured_output),
):
try:
profiling.sampling.sample.sample(
proc.pid,
duration_sec=0.5,
subproc.process.pid,
duration_sec=2.0,
sample_interval_usec=5000,
mode=1, # CPU mode
show_summary=False,
Expand All @@ -2690,8 +2705,8 @@ def main():
):
try:
profiling.sampling.sample.sample(
proc.pid,
duration_sec=0.5,
subproc.process.pid,
duration_sec=2.0,
sample_interval_usec=5000,
mode=0, # Wall-clock mode
show_summary=False,
Expand All @@ -2716,6 +2731,37 @@ def main():
self.assertIn("cpu_active_worker", wall_mode_output)
self.assertIn("idle_worker", wall_mode_output)

def test_cpu_mode_with_no_samples(self):
"""Test that CPU mode handles no samples gracefully when no samples are collected."""
# Mock a collector that returns empty stats
mock_collector = mock.MagicMock()
mock_collector.stats = {}
mock_collector.create_stats = mock.MagicMock()

with (
io.StringIO() as captured_output,
mock.patch("sys.stdout", captured_output),
mock.patch("profiling.sampling.sample.PstatsCollector", return_value=mock_collector),
mock.patch("profiling.sampling.sample.SampleProfiler") as mock_profiler_class,
):
mock_profiler = mock.MagicMock()
mock_profiler_class.return_value = mock_profiler

profiling.sampling.sample.sample(
12345, # dummy PID
duration_sec=0.5,
sample_interval_usec=5000,
mode=1, # CPU mode
show_summary=False,
all_threads=True,
)

output = captured_output.getvalue()

# Should see the "No samples were collected" message
self.assertIn("No samples were collected", output)
self.assertIn("CPU mode", output)


class TestGilModeFiltering(unittest.TestCase):
"""Test GIL mode filtering functionality (--mode=gil)."""
Expand Down Expand Up @@ -2852,34 +2898,46 @@ def test_gil_mode_integration_behavior(self):
import time
import threading

gil_ready = threading.Event()

def gil_releasing_work():
time.sleep(999999)

def gil_holding_work():
gil_ready.set()
x = 1
while True:
x += 1

def main():
# Start both threads
# Start both threads
idle_thread = threading.Thread(target=gil_releasing_work)
cpu_thread = threading.Thread(target=gil_holding_work)
idle_thread.start()
cpu_thread.start()

# Wait for GIL-holding thread to be running, then signal test
gil_ready.wait()
_test_sock.sendall(b"threads_ready")

idle_thread.join()
cpu_thread.join()

main()
'''
with test_subprocess(gil_test_script) as proc:
with test_subprocess(gil_test_script) as subproc:
# Wait for signal that threads are running
response = subproc.socket.recv(1024)
self.assertEqual(response, b"threads_ready")

with (
io.StringIO() as captured_output,
mock.patch("sys.stdout", captured_output),
):
try:
profiling.sampling.sample.sample(
proc.pid,
duration_sec=0.5,
subproc.process.pid,
duration_sec=2.0,
sample_interval_usec=5000,
mode=2, # GIL mode
show_summary=False,
Expand All @@ -2897,7 +2955,7 @@ def main():
):
try:
profiling.sampling.sample.sample(
proc.pid,
subproc.process.pid,
duration_sec=0.5,
sample_interval_usec=5000,
mode=0, # Wall-clock mode
Expand Down
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