All files / urkel/lib/trie lockfile.js

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/*!
 * lockfile.js - lock file
 * Copyright (c) 2018, Christopher Jeffrey (MIT License).
 * https://github.com/handshake-org/urkel
 */
 
'use strict';
 
const assert = require('bsert');
const Path = require('path');
 
/**
 * LockFile
 */
 
class LockFile {
  constructor(fs, prefix) {
    assert(fs && typeof fs.write === 'function');
 
    this.fs = fs;
    this.file = '';
    this.attempts = 4;
    this.interval = 1500;
    this.retry = 1000;
    this.stale = 3500;
    this.timer = null;
 
    this.rename(prefix);
  }
 
  rename(prefix) {
    assert(typeof prefix === 'string');
    this.file = Path.resolve(prefix, 'lock');
  }
 
  async open() {
    for (let i = 0; i < this.attempts; i++) {
      const stat = await this.stat();
 
      if (stat) {
        const now = Date.now();
        const mtime = Math.round(stat.mtimeMs);
 
        // Somebody changed their system clock.
        if (mtime >= now + 10 * 1000) {
          await this.unlink();
          continue;
        }
 
        if (now < mtime + this.stale) {
          await this.wait();
          continue;
        }
      }
 
      try {
        if (!stat)
          await this.touch();
        else
          await this.update();
      } catch (e) {
        continue;
      }
 
      this.start();
 
      return;
    }
 
    throw new Error(`Could not acquire lock for: ${this.file}.`);
  }
 
  async close() {
    this.stop();
    return this.unlink();
  }
 
  start() {
    assert(this.timer == null);
 
    this.timer = setInterval(() => this.iterate(), this.interval);
 
    if (this.timer.unref)
      this.timer.unref();
  }
 
  stop() {
    assert(this.timer != null);
    clearInterval(this.timer);
    this.timer = null;
  }
 
  async iterate() {
    try {
      await this.update();
    } catch (e) {
      ;
    }
  }
 
  async stat() {
    let stat = null;
 
    try {
      stat = await this.fs.stat(this.file);
    } catch (e) {
      if (e.code !== 'ENOENT')
        throw e;
    }
 
    return stat;
  }
 
  async unlink() {
    try {
      await this.fs.unlink(this.file);
    } catch (e) {
      if (e.code !== 'ENOENT')
        throw e;
    }
  }
 
  async wait() {
    return new Promise(r => setTimeout(r, this.retry));
  }
 
  async touch() {
    const fd = await this.fs.open(this.file, 'wx', 0o640);
    return this.fs.close(fd);
  }
 
  async update() {
    return this.fs.truncate(this.file, 0);
  }
}
 
/*
 * Expose
 */
 
module.exports = LockFile;