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devexamples

Flock Mutex Critical Section

Prevent concurrent script runs with flock on a lockfile, distinguishing owner from contenders and timing out politely.

BashResilience

Code

snippet
#!/usr/bin/env bash
set -euo pipefail

readonly LOCK_FILE="/tmp/nightly-sync.lock"
readonly LOCK_WAIT=5

# 形态一：非阻塞抢锁，拿不到直接退出（调度器友好）
exec 9>"${LOCK_FILE}"
if ! flock -n 9; then
  echo "另一实例正在运行，跳过本次执行" >&2
  exit 0
fi

# 形态二：限时等待锁（需要排队的场景）
# flock -w "${LOCK_WAIT}" 9 || { echo "锁等待超时" >&2; exit 75; }

echo "获得锁，PID $$ 开始同步"

critical_section() {
  local started=$(date +%s)
  # ... 同步主体，异常退出时锁随文件描述符自动释放 ...
  sleep 2
  echo "同步完成，耗时 $(( $(date +%s) - started ))s"
}

critical_section

# 拿到锁后派生的后台任务也持锁，需要先关描述符
exec 9>&-
echo "锁已释放，脚本结束"

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