Os Thread Rseq

In this tutorial, you'll learn about How to Fix Restartable Sequences Errors. We cover key concepts, practical examples, and best practices.

Fix restartable sequences errors when thread-local counter updated without CPU migration safety.

Quick Fix

Wrong

import threading
counter=0
def worker():
    global counter
    for _ in range(100000): counter+=1

Thread may be migrated to another CPU between reading and writing counter. Race even with per-thread data?

Right

# rseq: per-CPU data with atomic restart on migration
# Python doesn't expose rseq directly, but it's used internally:
# Each thread has per-CPU variable. If thread migrates, sequence aborts and retries.
# Use per-CPU data structures for performance:
import os
cpu=os.sched_getcpu()
print(f'Running on CPU {cpu}')
# Pin thread to CPU to guarantee no migration:
os.sched_setaffinity(0, {cpu})
print('Thread pinned. No migration, rseq not needed.')

Thread pinned to CPU. No migration. Simple per-CPU access without rseq.

Prevention

Pin threads to avoid migration. rseq provides atomic per-CPU operations for kernel use.

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FAQ