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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：
- 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；
- 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
- 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。
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