利用Gearman实现并发查询（Multi-Query）

这个例子是想从数据库查询出几个结果集，一般的做法是，一个接一个的发送查询，然后汇总结果进行输出。

下面我们利用Gearman的gearman_client_run_tasks实现并发的查询，gearman_client_run_tasks接口可以一次性的提交多个任务，然后在callback函数中异步的处理结果。

PHP的示例如下：

The client:

<?php

$client = new GearmanClient();
$client->addServer();

// initialize the results of our 3 "query results" here
$userInfo = $friends = $posts = null;

// This sets up what gearman will callback to as tasks are returned to us.
// The $context helps us know which function is being returned so we can 
// handle it correctly.
$client->setCompleteCallback(function(GearmanTask $task, $context) use (&$userInfo, &$friends, &$posts) {
    switch($context) {
        case 'lookup_user':
            $userInfo = $task->data();
            break;
        case 'baconate':
            $friends = $task->data();
            break;
        case 'get_latest_posts_by':
            $posts = $task->data();
            break;
    }
});

// Here we queue up multiple tasks to be execute in *as much* parallelism as gearmand can give us
$client->addTask('lookup_user', 'joe@joe.com', 'lookup_user');
$client->addTask('baconate', 'joe@joe.com', 'baconate');
$client->addTask('get_latest_posts_by', 'joe@joe.com', 'get_latest_posts_by');

echo "Fetching...\n";
$start = microtime(true);
$client->runTasks();
$totaltime = number_format(microtime(true) - $start, 2);

echo "Got user info in: $totaltime seconds:\n";
var_dump($userInfo, $friends, $posts);

The worker:

<?php

$worker = new GearmanWorker();
$worker->addServer();

$worker->addFunction('lookup_user', function(GearmanJob $job){
    // normally you'd so some very safe type checking and query binding to a database here.
    // ...and we're gonna fake that.
    sleep(3);
    return 'The user requested ('. $job->workload() .') is 7 feet tall and awesome';
});

$worker->addFunction('baconate', function(GearmanJob $job){
    sleep(3);
    return 'The user ('. $job->workload() .') is 1 degree away from Kevin Bacon';
});

$worker->addFunction('get_latest_posts_by', function(GearmanJob $job){
    sleep(3);
    return 'The user ('. $job->workload() .') has no posts, sorry!';
});

while ($worker->work());

运行结果：

Fetching...
Got user info in: 9.00 seconds:
string(59) "The user requested (joe@joe.com) is 7 feet tall and awesome"
string(56) "The user (joe@joe.com) is 1 degree away from Kevin Bacon"
string(43) "The user (joe@joe.com) has no posts, sorry!"</span>

发现还是用了9S时间，那是因为只有一个worker，它只能是顺序执行。

一起运行三个worker或更多，再来试试：

Fetching...
Got user info in: 3.00 seconds:
string(59) "The user requested (joe@joe.com) is 7 feet tall and awesome"
string(56) "The user (joe@joe.com) is 1 degree away from Kevin Bacon"
string(43) "The user (joe@joe.com) has no posts, sorry!"</span>

这只是一个并行执行的例子，实际应用中可以有更好的并发性能。