月下博客

CLI模式下Yii2的log问题追踪

allen

转载请注明出处：https://ssrvps.org/archives/4073

命令行下运行长时间任务，发现Yii2的log组件不能正常输出日志。空闲之余逐步追踪问题，终于发现原因，以下是问题追踪记录。

问题复现

为了复现问题，预先准备了log组件的配置：

// file: console/config/console-local.php
...
'components' => [
        'log' => [
            'flushInterval' => 10,
            'targets' => [
                'info' => [
                    'class' => 'yii/log/FileTarget',
                    'levels' => ['info'],
                    'logVars' => [],
                    'categories' => ['app'],
                    'logFile' => '@console/logs/info/' . date('Ymd') . '.log',
                    "prefix" => function ($message) {
                        return "";
                    }
                ],
                    ...
            ],
        ],
    ],
...

以及测试用例：

// file: console/controllers/TestController.php
namespace console/controllers;

use Yii;
use yii/console/Controller;

class TestController extends Controller
{
    public function actionShort()
    {
        Yii::info("This is a short test message", "app");
        sleep(3);
        Yii::info("Another short test message", "app");
        echo "Done!", PHP_EOL;
    }

    public function actionLong()
    {
        $count = 10000;
        for ($index = 0; $index < $count; ++ $index) {
            Yii::info("This is a long test message", "app");
            sleep(1);
            Yii::info("Another long test message", "app");
        }
        echo "Done!", PHP_EOL;
    }
}

命令行下执行./yii test/short，日志正常输出到指定的文件中；执行./yii test/long，使用tailf或者tail -f命令查看日志文件，未发现输出；按ctrl+c终止脚本，日志没有出现新信息。

问题分析

仔细分析，运行上述代码有两个问题：1. log组件中flushInterval参数设置每10条信息合并输出一次，实际中一直没有输出；2. 按ctrl+c终止脚本，缓冲的信息没有输出。

由于之前已经向Yii开发团队提交过一个log组件的bug（issue链接：https://github.com/yiisoft/yii2/issues/8036）。本次发现的问题暂不确定是Yii2的bug还是使用方法不当，毕竟（应该）很少人会使用命令行运行长时间任务。

查找问题

根据log组件的架构，可能出现问题的三个点事：

  1. Logger类，Yii2默认的log组件类，对外暴露打印日志的log/info/warning/error等方法；
  2. Dispatcher类，对消息进行分类，根据配置分发到具体负责输出的输出类
  3. Target的具体实现子类，这些子类实现消息的具体输出，例如保存到文件/数据库，或者发送邮件等。

根据这些线索，可以比较清晰的查看调用链条。

首先是Yii::info函数的调用，定义在BaseYii中，具体实现委托给Logger类的log方法:

// file: https://github.com/yiisoft/yii2/blob/master/framework/log/Logger.php
...
    /**
     * Logs a message with the given type and category.
     * If [[traceLevel]] is greater than 0, additional call stack information about
     * the application code will be logged as well.
     * @param string|array $message the message to be logged. This can be a simple string or a more
     * complex data structure that will be handled by a [[Target|log target]].
     * @param int $level the level of the message. This must be one of the following:
     * `Logger::LEVEL_ERROR`, `Logger::LEVEL_WARNING`, `Logger::LEVEL_INFO`, `Logger::LEVEL_TRACE`,
     * `Logger::LEVEL_PROFILE_BEGIN`, `Logger::LEVEL_PROFILE_END`.
     * @param string $category the category of the message.
     */
    public function log($message, $level, $category = 'application')
    {
        $time = microtime(true);
        $traces = [];
        if ($this->traceLevel > 0) {
            $count = 0;
            $ts = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
            array_pop($ts); // remove the last trace since it would be the entry script, not very useful
            foreach ($ts as $trace) {
                if (isset($trace['file'], $trace['line']) && strpos($trace['file'], YII2_PATH) !== 0) {
                    unset($trace['object'], $trace['args']);
                    $traces[] = $trace;
                    if (++$count >= $this->traceLevel) {
                        break;
                    }
                }
            }
        }
        $this->messages[] = [$message, $level, $category, $time, $traces, memory_get_usage()];
        if ($this->flushInterval > 0 && count($this->messages) >= $this->flushInterval) {
            $this->flush();
        }
    }
...

log方法功能是格式化消息，然后调用flush方法输出日志。接着看flush方法的实现：

// file: https://github.com/yiisoft/yii2/blob/master/framework/log/Logger.php
....
    /**
     * Flushes log messages from memory to targets.
     * @param bool $final whether this is a final call during a request.
     */
    public function flush($final = false)
    {
        $messages = $this->messages;
        // https://github.com/yiisoft/yii2/issues/5619
        // new messages could be logged while the existing ones are being handled by targets
        $this->messages = [];
        if ($this->dispatcher instanceof Dispatcher) {
            $this->dispatcher->dispatch($messages, $final);
        }
    }
....

flush方法委托Dispatcher将消息分发到具体的目标。继续跟踪前，先看看Logger类的init方法：

// file: https://github.com/yiisoft/yii2/blob/master/framework/log/Logger.php
...
    /**
     * Initializes the logger by registering [[flush()]] as a shutdown function.
     */
    public function init()
    {
        parent::init();
        register_shutdown_function(function () {
            // make regular flush before other shutdown functions, which allows session data collection and so on
            $this->flush();
            // make sure log entries written by shutdown functions are also flushed
            // ensure "flush()" is called last when there are multiple shutdown functions
            register_shutdown_function([$this, 'flush'], true);
        });
    }
...

logger组件初始化时，注册register_shutdown_function回调函数，确保脚本执行完毕时消息被正确打印。这也是在脚本中无论何时出现exit/die，或者调用Yii::$app->end()都会让日志正常输出的秘密。接下来看Dispatcher类的dispatch方法：

// file: https://github.com/yiisoft/yii2/blob/master/framework/log/Dispatcher.php
...
    /**
     * Dispatches the logged messages to [[targets]].
     * @param array $messages the logged messages
     * @param bool $final whether this method is called at the end of the current application
     */
    public function dispatch($messages, $final)
    {
        $targetErrors = [];
        foreach ($this->targets as $target) {
            if ($target->enabled) {
                try {
                    $target->collect($messages, $final);
                } catch (/Exception $e) {
                    $target->enabled = false;
                    $targetErrors[] = [
                        'Unable to send log via ' . get_class($target) . ': ' . ErrorHandler::convertExceptionToString($e),
                        Logger::LEVEL_WARNING,
                        __METHOD__,
                        microtime(true),
                        [],
                    ];
                }
            }
        }

        if (!empty($targetErrors)) {
            $this->dispatch($targetErrors, true);
        }
    }
...

dispatch让具体负责输出的target类收集信息，如果期间出现异常，关闭该渠道，将信息以warning级别输出。接下来跟踪target的collect方法，该方法定义在抽象类Target中：

// file: https://github.com/yiisoft/yii2/blob/master/framework/log/Target.php
...
    /**
     * Processes the given log messages.
     * This method will filter the given messages with [[levels]] and [[categories]].
     * And if requested, it will also export the filtering result to specific medium (e.g. email).
     * @param array $messages log messages to be processed. See [[Logger::messages]] for the structure
     * of each message.
     * @param bool $final whether this method is called at the end of the current application
     */
    public function collect($messages, $final)
    {
        $this->messages = array_merge($this->messages, static::filterMessages($messages, $this->getLevels(), $this->categories, $this->except));
        $count = count($this->messages);
        if ($count > 0 && ($final || $this->exportInterval > 0 && $count >= $this->exportInterval)) {
            if (($context = $this->getContextMessage()) !== '') {
                $this->messages[] = [$context, Logger::LEVEL_INFO, 'application', YII_BEGIN_TIME];
            }
            // set exportInterval to 0 to avoid triggering export again while exporting
            $oldExportInterval = $this->exportInterval;
            $this->exportInterval = 0;
            $this->export();
            $this->exportInterval = $oldExportInterval;

            $this->messages = [];
        }
    }
....

collect方法的作用：1. 调用filterMessages方法过滤日志信息； 2. 判断是否达到输出条件，然后调用子类的export方法实现日志的具体输出。从collect方法，可以看到第一问题的原因：target类有exportInterval参数，默认是1000，示例代码要运行非常长的时间才会收集到如此多的消息，如果需要及时查看，可将配置代码改成如下：

// file: console/config/console-local.php
...
'components' => [
        'log' => [
            'flushInterval' => 10,
            'targets' => [
                'info' => [
                    'class' => 'yii/log/FileTarget',
                            'exportInterval' => 1,
                    'levels' => ['info'],
                            'logVars' => [],
                    'categories' => ['app'],
                    'logFile' => '@console/logs/info/' . date('Ymd') . '.log',
                    "prefix" => function ($message) {
                        return "";
                    }
                ],
                    ...
            ],
        ],
    ],
...

接着再看中断脚本日志不输出的问题。前面已经提到，日志输出的技巧是注册了register_shutdown_function回调。先看看这个函数的官方解释：

注册一个 callback ，它会在脚本执行完成或者 exit() 后被调用。

可以多次调用 register_shutdown_function() ，这些被注册的回调会按照他们注册时的顺序被依次调用。 如果你在注册的方法内部调用 exit()， 那么所有处理会被中止，并且其他注册的中止回调也不会再被调用。

Note:

如果进程被信号SIGTERM或SIGKILL杀死，那么中止函数将不会被调用。尽管你无法中断SIGKILL，但你可以通过pcntl_signal() 来捕获SIGTERM，通过在其中调用exit()来进行一个正常的中止。

根据解释，register_shutdown_function注册的函数将在脚本执行完成或者exit后被调用。但是SIGTERM/SIGKILL等信号，不会回调注册的函数，并且经过测试ctrl+c（发出SIGINT信号）也不会触发回调。

脚本未正常执行完被终止，该如何处理？根据文档提示，需要使用pcntl_signal函数捕捉信号，再调用exit函数让脚本正常退出，此时register_shutdown_function注册的函数会被正常回调。

将示例函数的方法改成：

// file: console/controllers/TestController.php
...
    public function actionLong()
    {
        declare(ticks=1);
        pcntl_signal(SIGINT, function() {exit();});
        pcntl_signal(SIGTERM, function() {exit();});
        pcntl_signal(SIGKILL, function() {exit();});
        $count = 10000;
        for ($index = 0; $index < $count; ++ $index) {
            Yii::info("This is a long test message", "app");
            sleep(1);
            Yii::info("Another long test message", "app");
        }
        echo "Done!", PHP_EOL;
    }
....

然后在脚本执行过程中，按下ctrl_+c，或者通过kill命令发送信号，日志都正常输出，表明register_shutdown_function中的回调函数被正常调用。

总结

发现的两个问题，第一个并非Yii2的bug，而是未全面理解文档导致（Logger类的flushInterval和具体Target类的exportInterval都需要设置一个合适的值，才能及时查看消息）；第二个问题有点蛋疼，应该算PHP的坑。好在非命令行情况下，pcntl拓展不可用，在web开发中不会出现类似问题。

参考

  1. http://www.yiiframework.com/doc-2.0/guide-runtime-logging.html
  2. http://php.net/manual/zh/function.register-shutdown-function.php
  3. http://php.net/manual/zh/function.pcntl-signal.php
  4. https://stackoverflow.com/questions/3909798/phps-register-shutdown-function-to-fire-when-a-script-is-killed-from-the-comman