Redis信号量锁无法释放

Question

我正在使用 redis-semaphore gem，版本 0.3.1。

出于某种原因，我有时无法释放过时的 Redis 锁。根据我的分析，如果我的 Docker 进程在创建锁后崩溃，这似乎会发生。

我在下面描述了我的调试过程，想知道是否有人可以建议如何进一步调试。

假设我们要用这个名字创建一个redis锁：

name = "test"

我们在两个不同的终端中插入这个变量windows。首先，我们运行:

def lock_for_15_secs(name)
  job = Redis::Semaphore.new(name.to_sym, redis: NonBlockingRedis.new(), custom_blpop: true, :stale_client_timeout => 15)
  if job.lock(-1) == "0"
    puts "Locked and starting"
    sleep(15)
    puts "Now it's stale, try to release in another process"
    sleep(15)
    puts "Now trying to unlock"
    unlock = job.unlock
    puts unlock == false ? "Wuhuu, already unlocked" : "Hm, should have been unlocked by another process, but wasn't"
  end
end
lock_for_15_secs(name)

第二个我们运行:

def release_and_lock(name)
  job     = Redis::Semaphore.new(name.to_sym, redis: NonBlockingRedis.new(), custom_blpop: true, :stale_client_timeout => 15)
  release = job.release_stale_locks!
  count   = job.available_count
  puts "Release reponse is #{release.inspect} and available count is #{count}"
  if job.lock(-1) == "0"
    puts "Wuhuu, we can lock it"
    job.unlock
  else
    puts "Hmm, we can't lock it"
  end
end
release_and_lock(name)

这通常会按预期进行。 15 秒后，第二个终端无法释放锁，但是当 15 秒后运行时，它会释放。以下是 release_and_lock(name).

的输出

15 秒后：

irb(main):1:0> release_and_lock(name)
Release reponse is {"0"=>"1580292557.321834"} and available count is 0
Hmm, we can't lock it
=> nil

15 秒后：

irb(main):2:0> release_and_lock(name)
Release reponse is {"0"=>"1580292557.321834"} and available count is 1
Wuhuu, we can lock it
=> 1
irb(main):3:0> release_and_lock(name)
Release reponse is {} and available count is 1
Wuhuu, we can lock it

但是每当我看到一个陈旧的锁没有被释放，并且我运行 release_and_lock(name) 进行诊断时，就会返回：

irb(main):4:0> release_and_lock(name)
Release reponse is {} and available count is 0
Hmm, we can't lock it

此时我唯一的选择是刷新 redis:

require 'non_blocking_redis'
non_blocking_redis = NonBlockingRedis.new()
non_blocking_redis.flushall

P.s。我的 NonBlockingRedis 继承自 Redis:

class Redis
  class Semaphore
    def initialize(name, opts = {})
      @custom_opts          = opts
      @name                 = name
      @resource_count       = opts.delete(:resources) || 1
      @stale_client_timeout = opts.delete(:stale_client_timeout)
      @redis                = opts.delete(:redis) || Redis.new(opts)
      @use_local_time       = opts.delete(:use_local_time)
      @custom_blpop         = opts.delete(:custom_blpop) # false=queue, true=cancel
      @tokens               = []
    end

    def lock(timeout = 0)
      exists_or_create!
      release_stale_locks! if check_staleness?
      token_pair    = @redis.blpop(available_key, timeout, @custom_blpop)
      return false if token_pair.nil?
      current_token = token_pair[1]
      @tokens.push(current_token)
      @redis.hset(grabbed_key, current_token, current_time.to_f)
      if block_given?
        begin
          yield current_token
        ensure
          signal(current_token)
        end
      end
      current_token
    end
    alias_method :wait, :lock
  end
end

class NonBlockingRedis < Redis

  def initialize(options = {})
    if options.empty?
      options = {
        url: Rails.application.secrets.redis_url,
        db:  Rails.application.secrets.redis_sidekiq_db,
        driver: :hiredis,
        network_timeout: 5
      }
    end

    super(options)
  end

  def blpop(key, timeout, custom_blpop)
    if custom_blpop
      if timeout == -1
        result = lpop(key)
        return result if result.nil?
        return [key, result]
      else
        super(key, timeout)
      end
    else
       super
    end
  end

  def lock(timeout = 0)
    exists_or_create!
    release_stale_locks! if check_staleness?
    token_pair = @redis.blpop(available_key, timeout, @custom_blpop)
    return false if token_pair.nil?
    current_token = token_pair[1]
    @tokens.push(current_token)
    @redis.hset(grabbed_key, current_token, current_time.to_f)
    if block_given?
      begin
        yield current_token
      ensure
        signal(current_token)
      end
    end
    current_token
  end
  alias_method :wait, :lock
end

require 'non_blocking_redis'

Answer 1

一个很棒的错误

错误

我认为如果在 SEMAPHORE:test:AVAILABLE

上执行 lpop 时终止进程，就会发生这种情况

最有可能在这里https://github.com/dv/redis-semaphore/blob/v0.3.1/lib/redis/semaphore.rb#L67

复制它

NonBlockingRedis.new.flushall

release_and_lock('test');

NonBlockingRedis.new.lpop('SEMAPHORE:test:AVAILABLE')

现在最初你有：

SEMAPHORE:test:AVAILABLE                0
SEMAPHORE:test:VERSION          1
SEMAPHORE:test:EXISTS           1

以上代码后得到：

SEMAPHORE:test:VERSION          1
SEMAPHORE:test:EXISTS           1

代码检查 SEMAPHORE:test:EXISTS 然后期望有 SEMAPHORE:test:AVAILABLE / SEMAPHORE:test:GRABBED

解决方案

根据我的简要检查，我认为不修改 gem 是不可能的。我尝试添加一个 expiration: 但不知何故它设法禁用了 SEMAPHORE:test:EXISTS

的过期

NonBlockingRedis.new.ttl('SEMAPHORE:test:EXISTS') # => -1 and it should have been e.g. 20 seconds and going down

所以..也许会有一个修复

class Redis
  class Semaphore
    def exists_or_create!
      token = @redis.getset(exists_key, EXISTS_TOKEN)

      if token.nil? || all_tokens.empty?
        create!
      else
        # Previous versions of redis-semaphore did not set `version_key`.
        # Make sure it's set now, so we can use it in future versions.

        if token == API_VERSION && @redis.get(version_key).nil?
          @redis.set(version_key, API_VERSION)
        end

        true
      end
    end
  end
end

all_tokens 是 https://github.com/dv/redis-semaphore/blob/v0.3.1/lib/redis/semaphore.rb#L120

我很快会打开一个 PR 到 gem -> https://github.com/dv/redis-semaphore/pull/66 也许 ‍♂️

备注 1

不确定您如何使用 NonBlockingRedis，但它未在 Redis::Semaphore 中使用。你做 lock(-1) 代码 lpop。此外，代码永远不会调用您的 lock.

随机

这是一个转储密钥的助手

class Test
  def self.all
    r = NonBlockingRedis.new
    puts r.keys('*').map { |k|
      [
        k,
        ((r.hgetall(k) rescue r.get(k)) rescue r.lrange(k, 0, -1).join(' | '))
      ].join("\t\t")
    }
  end
end

> Test.all

SEMAPHORE:test:AVAILABLE                0
SEMAPHORE:test:VERSION          1
SEMAPHORE:test:EXISTS           1

为完整起见，这里是您抓住锁后的样子

SEMAPHORE:test:VERSION          1
SEMAPHORE:test:EXISTS           1
SEMAPHORE:test:GRABBED          {"0"=>"1583672948.7168388"}

Redis信号量锁无法释放

Redis semaphore locks can't be released

ruby

mutex

semaphore

redis

错误

解决方案

备注 1

随机