场景

laravel 为追求轻量化，使用redis实现了mq替代rocketmq,那么laravel是怎么保证消息一定被消费呢? 下面分析下php artisan queue:work源码

总结

源码解析篇幅太长，这里总结下为什么redis list做队列却可以做到不丢数据?
1.lua脚本弹出job之后 先放入queue:name:reserved zset中
2. 执行过程中遇到异常 则将job从queue:name:reserved删除，并放入queue:name:delayed中
3. 每次弹job之前，先将reserved,delayed超时的job放入queue:name中
4.一旦达到了最大重试次数 则删除job, 且可以保存失败任务到数据库中。 这是保底策略

源码分析

1. 源码位置 Illuminate\Queue\Console\WorkCommand.php
2. WorkCommand handle 方法

   $this->listenForEvents() 监听任务执行前事件，执行完事件,失败事件， 失败时 可以存储失败的任务
   获取queue链接和queueName,然后调用Illuminate\Queue\Worker类.daemon方法

    /**
     * Execute the console command.
     *
     * @return int|null
     */
    public function handle()
    {
        if ($this->downForMaintenance() && $this->option('once')) {
            return $this->worker->sleep($this->option('sleep'));
        }

   		// 监听任务执行前事件，执行完事件,失败事件
        $this->listenForEvents();

        $connection = $this->argument('connection')
                        ?: $this->laravel['config']['queue.default'];

        $queue = $this->getQueue($connection);
		// 调用Illuminate\Queue\Worker类.daemon方法
        return $this->runWorker(
            $connection, $queue
        );
    }

    /**
     * Listen for the queue events in order to update the console output.
     *
     * @return void
     */
    protected function listenForEvents()
    {
        $this->laravel['events']->listen(JobProcessing::class, function ($event) {
            $this->writeOutput($event->job, 'starting');
        });

        $this->laravel['events']->listen(JobProcessed::class, function ($event) {
            $this->writeOutput($event->job, 'success');
        });

        $this->laravel['events']->listen(JobFailed::class, function ($event) {
            $this->writeOutput($event->job, 'failed');

            $this->logFailedJob($event);
        });
    }

3. 调用Illuminate\Queue\Worker类.daemon方法

public function daemon($connectionName, $queue, WorkerOptions $options)
    {
    	// 注册一些信号
        if ($supportsAsyncSignals = $this->supportsAsyncSignals()) {
            $this->listenForSignals();
        }

        $lastRestart = $this->getTimestampOfLastQueueRestart();

        [$startTime, $jobsProcessed] = [hrtime(true) / 1e9, 0];

        while (true) {
            if (! $this->daemonShouldRun($options, $connectionName, $queue)) {
                $status = $this->pauseWorker($options, $lastRestart);

                if (! is_null($status)) {
                    return $this->stop($status);
                }

                continue;
            }

            if (isset($this->resetScope)) {
                ($this->resetScope)();
            }

            // 弹出job, 这里是重点
            $job = $this->getNextJob(
                $this->manager->connection($connectionName), $queue
            );

            if ($supportsAsyncSignals) {
                $this->registerTimeoutHandler($job, $options);
            }

            
            if ($job) {
                $jobsProcessed++;
				// 重点  开始运行job
                $this->runJob($job, $connectionName, $options);

                if ($options->rest > 0) {
                    $this->sleep($options->rest);
                }
            } else {
                $this->sleep($options->sleep);
            }

			// 注册SIGALRM信号处理回调函数(退出),并设置时钟 时钟取自timeout选项
            if ($supportsAsyncSignals) {
                $this->resetTimeoutHandler();
            }

            // Finally, we will check to see if we have exceeded our memory limits or if
            // the queue should restart based on other indications. If so, we'll stop
            // this worker and let whatever is "monitoring" it restart the process.
            $status = $this->stopIfNecessary(
                $options, $lastRestart, $startTime, $jobsProcessed, $job
            );

            if (! is_null($status)) {
                return $this->stop($status);
            }
        }
    }
    protected function registerTimeoutHandler($job, WorkerOptions $options)
    {
        // We will register a signal handler for the alarm signal so that we can kill this
        // process if it is running too long because it has frozen. This uses the async
        // signals supported in recent versions of PHP to accomplish it conveniently.
        pcntl_signal(SIGALRM, function () use ($job, $options) {
            if ($job) {
                $this->markJobAsFailedIfWillExceedMaxAttempts(
                    $job->getConnectionName(), $job, (int) $options->maxTries, $e = $this->maxAttemptsExceededException($job)
                );

                $this->markJobAsFailedIfWillExceedMaxExceptions(
                    $job->getConnectionName(), $job, $e
                );

                $this->markJobAsFailedIfItShouldFailOnTimeout(
                    $job->getConnectionName(), $job, $e
                );
            }

            $this->kill(static::EXIT_ERROR);
        });

        pcntl_alarm(
            max($this->timeoutForJob($job, $options), 0)
        );
    }
protected function getNextJob($connection, $queue)
    {
        $popJobCallback = function ($queue) use ($connection) {
            return $connection->pop($queue);
        };

        try {
            if (isset(static::$popCallbacks[$this->name])) {
                return (static::$popCallbacks[$this->name])($popJobCallback, $queue);
            }

            foreach (explode(',', $queue) as $queue) {
                if (! is_null($job = $popJobCallback($queue))) {
                    return $job;
                }
            }
        } catch (Throwable $e) {
            $this->exceptions->report($e);

            $this->stopWorkerIfLostConnection($e);

            $this->sleep(1);
        }
    }

1. $this->getNextJob 弹出job, 这里是重点, Illuminate\Queue\RedisQueue的pop方法

第一步： $this->migrate方法 使用lua脚本将queues:name:reserved queues:name:delayed时间超时的job 重新放入queue:name list中
第二步: retrieveNextJob 方式使用lua脚本将 queue:name中弹出一个job,并把这个job放入queues:name:reserved zset中，返回封装的redisJob

    /**
     * Pop the next job off of the queue.
     *
     * @param  string|null  $queue
     * @return \Illuminate\Contracts\Queue\Job|null
     */
    public function pop($queue = null)
    {
        // 将queues:name:reserved  queues:name:delayed时间超时的job 重新放入queue:name list中
        $this->migrate($prefixed = $this->getQueue($queue));

        [$job, $reserved] = $this->retrieveNextJob($prefixed);

        if ($reserved) {
            return new RedisJob(
                $this->container, $this, $job,
                $reserved, $this->connectionName, $queue ?: $this->default
            );
        }
    }

    protected function migrate($queue)
    {
        $this->migrateExpiredJobs($queue.':delayed', $queue);

        if (! is_null($this->retryAfter)) {
            $this->migrateExpiredJobs($queue.':reserved', $queue);
        }
    }
        public static function migrateExpiredJobs()
    {
        return <<<'LUA'
-- Get all of the jobs with an expired "score"...
local val = redis.call('zrangebyscore', KEYS[1], '-inf', ARGV[1])

-- If we have values in the array, we will remove them from the first queue
-- and add them onto the destination queue in chunks of 100, which moves
-- all of the appropriate jobs onto the destination queue very safely.
if(next(val) ~= nil) then
    redis.call('zremrangebyrank', KEYS[1], 0, #val - 1)

    for i = 1, #val, 100 do
        redis.call('rpush', KEYS[2], unpack(val, i, math.min(i+99, #val)))
        -- Push a notification for every job that was migrated...
        for j = i, math.min(i+99, #val) do
            redis.call('rpush', KEYS[3], 1)
        end
    end
end

return val
LUA;


    /**
     * Retrieve the next job from the queue.
     *
     * @param  string  $queue
     * @param  bool  $block
     * @return array
     */
    protected function retrieveNextJob($queue, $block = true)
    {
        $nextJob = $this->getConnection()->eval(
            LuaScripts::pop(), 3, $queue, $queue.':reserved', $queue.':notify',
            $this->availableAt($this->retryAfter)
        );

        if (empty($nextJob)) {
            return [null, null];
        }

        [$job, $reserved] = $nextJob;

        if (! $job && ! is_null($this->blockFor) && $block &&
            $this->getConnection()->blpop([$queue.':notify'], $this->blockFor)) {
            return $this->retrieveNextJob($queue, false);
        }

        return [$job, $reserved];
    }
    public static function pop()
    {
        return <<<'LUA'
-- Pop the first job off of the queue...
local job = redis.call('lpop', KEYS[1])
local reserved = false

if(job ~= false) then
    -- Increment the attempt count and place job on the reserved queue...
    reserved = cjson.decode(job)
    reserved['attempts'] = reserved['attempts'] + 1
    reserved = cjson.encode(reserved)
    redis.call('zadd', KEYS[2], ARGV[1], reserved)
    redis.call('lpop', KEYS[3])
end

return {job, reserved}
LUA;

2. registerTimeoutHandler 注册SIGALRM信号处理回调函数(退出),并设置时钟 时钟取自timeout选项
3. runJob —> process方法

第一步： 分发JobProcessing事件
第二步: markJobAsFailedIfAlreadyExceedsMaxAttempts 如果超过最大重试次数 则分发JobFailed事件 JobProcessed时间,删除job, 顺带执行下job的failed回调函数

 /**
     * Process the given job from the queue.
     *
     * @param  string  $connectionName
     * @param  \Illuminate\Contracts\Queue\Job  $job
     * @param  \Illuminate\Queue\WorkerOptions  $options
     * @return void
     *
     * @throws \Throwable
     */
    public function process($connectionName, $job, WorkerOptions $options)
    {
        try {
     
            $this->raiseBeforeJobEvent($connectionName, $job);
			
			// 检查最大重试次数
            $this->markJobAsFailedIfAlreadyExceedsMaxAttempts(
                $connectionName, $job, (int) $options->maxTries
            );

            if ($job->isDeleted()) {
                return $this->raiseAfterJobEvent($connectionName, $job);
            }

            //  we will fire off the job and let it process. We will catch any exceptions so
            // they can be reported to the developers logs, etc. Once the job is finished the
            // proper events will be fired to let any listeners know this job has finished.
            $job->fire();

            $this->raiseAfterJobEvent($connectionName, $job);
        } catch (Throwable $e) {
            $this->handleJobException($connectionName, $job, $options, $e);
        }
    }

4. fire 执行job的handle方法

    /**
     * Fire the job.
     *
     * @return void
     */
    public function fire()
    {
        $payload = $this->payload();

        [$class, $method] = JobName::parse($payload['job']);

        ($this->instance = $this->resolve($class))->{$method}($this, $payload['data']);
    }

5. 执行过程捕捉到了异常 则job 从queues:foo:reserved 放入queues:foo:delayed中

    /**
     * Handle an exception that occurred while the job was running.
     *
     * @param  string  $connectionName
     * @param  \Illuminate\Contracts\Queue\Job  $job
     * @param  \Illuminate\Queue\WorkerOptions  $options
     * @param  \Throwable  $e
     * @return void
     *
     * @throws \Throwable
     */
    protected function handleJobException($connectionName, $job, WorkerOptions $options, Throwable $e)
    {
        try {
            if (! $job->hasFailed()) {
                $this->markJobAsFailedIfWillExceedMaxAttempts(
                    $connectionName, $job, (int) $options->maxTries, $e
                );

                $this->markJobAsFailedIfWillExceedMaxExceptions(
                    $connectionName, $job, $e
                );
            }

            $this->raiseExceptionOccurredJobEvent(
                $connectionName, $job, $e
            );
        } finally {
            // 首次异常
            if (! $job->isDeleted() && ! $job->isReleased() && ! $job->hasFailed()) {
                $job->release($this->calculateBackoff($job, $options));
            }
        }

        throw $e;
    }
    /**
     * Release the job back into the queue.
     *
     * @param  int  $delay
     * @return void
     */
    public function release($delay = 0)
    {
        parent::release($delay);

        $this->redis->deleteAndRelease($this->queue, $this, $delay);
    }
    
    /**
     * Delete a reserved job from the reserved queue and release it.
     *
     * @param  string  $queue
     * @param  \Illuminate\Queue\Jobs\RedisJob  $job
     * @param  int  $delay
     * @return void
     */
    public function deleteAndRelease($queue, $job, $delay)
    {
        $queue = $this->getQueue($queue);

        $this->getConnection()->eval(
            LuaScripts::release(), 2, $queue.':delayed', $queue.':reserved',
            $job->getReservedJob(), $this->availableAt($delay)
        );
    }
    /**
     * Get the Lua script for releasing reserved jobs.
     *
     * KEYS[1] - The "delayed" queue we release jobs onto, for example: queues:foo:delayed
     * KEYS[2] - The queue the jobs are currently on, for example: queues:foo:reserved
     * ARGV[1] - The raw payload of the job to add to the "delayed" queue
     * ARGV[2] - The UNIX timestamp at which the job should become available
     *
     * @return string
     */
    public static function release()
    {
        return <<<'LUA'
-- Remove the job from the current queue...
redis.call('zrem', KEYS[2], ARGV[1])

-- Add the job onto the "delayed" queue...
redis.call('zadd', KEYS[1], ARGV[2], ARGV[1])

return true
LUA;
    }