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REASY/gil_threads.py

Created December 15, 2025 03:51
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Python: Multi-Threading with GIL and Free-Threading
Raw
gil_threads.py
import threading
import sys
import time
import os
from typing import List, NamedTuple
# Optional import for visualization
try:
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
HAS_MATPLOTLIB = True
except ImportError:
HAS_MATPLOTLIB = False
# --- Configuration ---
CHUNK_SIZE = 1_000 # Smaller chunks for better resolution
TOTAL_ITERS = 20_000_000 # Total work per thread
NUM_THREADS = 8 # Keep it clean
class TaskEvent(NamedTuple):
thread_id: int
start_time: float
end_time: float
class CpuBoundTask:
def __init__(self, thread_id: int, collector: ThreadSafeResultCollector):
self.thread_id = thread_id
self.num_chunks = TOTAL_ITERS // CHUNK_SIZE
self.collector = collector
def run(self) -> None:
local_events: List[TaskEvent] = []
for _ in range(self.num_chunks):
t0 = time.perf_counter()
# Burn CPU
val = 0
for i in range(CHUNK_SIZE):
val += i % 256
t1 = time.perf_counter()
local_events.append(TaskEvent(self.thread_id, t0, t1))
self.collector.add_result(local_events)
class ThreadSafeResultCollector:
def __init__(self) -> None:
self._results: List[TaskEvent] = []
self._lock = threading.Lock()
def add_result(self, events: List[TaskEvent]) -> None:
with self._lock:
self._results.extend(events)
def get_results(self) -> List[TaskEvent]:
with self._lock:
# Return a shallow copy to prevent external modification issues
return list(self._results)
def plot_timeline(history: List[TaskEvent]):
if not history:
print("No history recorded.")
return
if not HAS_MATPLOTLIB:
print("Error: matplotlib is not installed. Visualization disabled.")
return
# Normalize times
min_t = min(e.start_time for e in history)
max_t = max(e.end_time for e in history)
total_duration_ms = (max_t - min_t) * 1000
# Setup Plot
fig, ax = plt.subplots(figsize=(12, 6))
# Distinct colors for threads
colors = plt.cm.get_cmap("tab10", NUM_THREADS)
# Plot each chunk as a horizontal bar
# (y, width, height, left)
bar_height = 0.8
print("Rendering plot...")
for tid in range(NUM_THREADS):
events = sorted(
[e for e in history if e.thread_id == tid], key=lambda x: x.start_time
)
if not events:
continue
# Add broken barh
ranges = []
for e in events:
start_norm = (e.start_time - min_t) * 1000 # Convert to ms
duration = (e.end_time - e.start_time) * 1000
ranges.append((start_norm, duration))
ax.broken_barh(
ranges, (tid - bar_height / 2, bar_height), facecolors=colors(tid)
)
# Detect GIL status for title
is_gil_enabled = True
if hasattr(sys, "_is_gil_enabled"):
is_gil_enabled = sys._is_gil_enabled() # type: ignore
mode = (
"Standard (GIL Enabled)" if is_gil_enabled else "Free-Threading (GIL Disabled)"
)
ax.set_yticks(range(NUM_THREADS))
ax.set_yticklabels([f"Thread {i}" for i in range(NUM_THREADS)])
ax.set_xlabel("Time (milliseconds)")
# Updated title with total duration
title = (
f"Python Thread Scheduling Visualization\n"
f"{sys.version.split()[0]} - {mode}\n"
f"Total Duration: {total_duration_ms:.2f} ms"
)
ax.set_title(title)
ax.grid(True, axis="x", linestyle="--", alpha=0.7)
plt.tight_layout()
plt.show()
def report_text(history: List[TaskEvent]):
if not history:
print("No history recorded.")
return
min_t = min(e.start_time for e in history)
max_t = max(e.end_time for e in history)
total_duration = max_t - min_t
print("-" * 40)
print(f"Total Execution Time: {total_duration:.4f}s")
print("-" * 40)
# Calculate per-thread active time
thread_durations = {}
for e in history:
thread_durations[e.thread_id] = thread_durations.get(e.thread_id, 0.0) + (
e.end_time - e.start_time
)
print("Active CPU Time per Thread:")
for tid in sorted(thread_durations.keys()):
print(f" Thread {tid}: {thread_durations[tid]:.4f}s")
def main() -> None:
# Detect GIL status
is_gil_enabled = True
if hasattr(sys, "_is_gil_enabled"):
is_gil_enabled = sys._is_gil_enabled() # type: ignore
mode = "Standard (GIL)" if is_gil_enabled else "Free-Threading (No GIL)"
print(f"Python: {sys.version}")
print(f"Mode: {mode}")
print(f"Running {NUM_THREADS} threads...")
collector = ThreadSafeResultCollector()
threads = [
threading.Thread(target=CpuBoundTask(i, collector).run)
for i in range(NUM_THREADS)
]
start_time = time.time()
for t in threads:
t.start()
for t in threads:
t.join()
# Check env var. Default to False (Text only) unless explicitly set to '1' or 'true'
visualize_env = os.environ.get("VISUALIZE", "0").lower()
should_visualize = visualize_env in ("1", "true", "yes", "on")
if should_visualize:
plot_timeline(collector.get_results())
else:
report_text(collector.get_results())
print("\nTip: Set VISUALIZE=1 to see the Matplotlib graph.")
if __name__ == "__main__":
main()
@REASY
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REASY commented Dec 15, 2025 

(python-gil) ➜  python-gil uv run --python 3.14t /usr/bin/time -pv python gil_v11.py
Python: 3.14.2 free-threading build (main, Dec  9 2025, 19:03:17) [Clang 21.1.4 ]
Mode:   Free-Threading (No GIL)
Running 8 threads...
----------------------------------------
Total Execution Time: 0.3225s
----------------------------------------
Active CPU Time per Thread:
  Thread 0: 0.3104s
  Thread 1: 0.3168s
  Thread 2: 0.3081s
  Thread 3: 0.3130s
  Thread 4: 0.3119s
  Thread 5: 0.3074s
  Thread 6: 0.3081s
  Thread 7: 0.3048s

Tip: Set VISUALIZE=1 to see the Matplotlib graph.
        Command being timed: "python gil_v11.py"
        User time (seconds): 2.50
        System time (seconds): 0.01
        Percent of CPU this job got: 658%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.38
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 61344
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 14107
        Voluntary context switches: 185
        Involuntary context switches: 45
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0
(python-gil) ➜  python-gil uv run --python python /usr/bin/time -pv python gil_v11.py
Python: 3.14.2 (main, Dec  9 2025, 19:03:28) [Clang 21.1.4 ]
Mode:   Standard (GIL)
Running 8 threads...
----------------------------------------
Total Execution Time: 2.2919s
----------------------------------------
Active CPU Time per Thread:
  Thread 0: 1.5147s
  Thread 1: 2.1062s
  Thread 2: 1.8900s
  Thread 3: 1.7269s
  Thread 4: 1.7083s
  Thread 5: 0.8628s
  Thread 6: 2.0455s
  Thread 7: 1.6888s

Tip: Set VISUALIZE=1 to see the Matplotlib graph.
        Command being timed: "python gil_v11.py"
        User time (seconds): 4.42
        System time (seconds): 0.03
        Percent of CPU this job got: 177%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:02.51
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 92320
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 18225
        Voluntary context switches: 3705
        Involuntary context switches: 274
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

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REASY commented Dec 15, 2025

FreeThreading GIL

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