Support async logging

[chenBright]

What problem does this PR solve?

Issue Number:

Problem Summary:

What is changed and the side effects?

Changed:

使用ExecutionQueue的相关技术支持异步日志

Side effects:

• Performance effects(性能影响):

• Breaking backward compatibility(向后兼容性):

---

Check List:

• Please make sure your changes are compilable(请确保你的更改可以通过编译).
• When providing us with a new feature, it is best to add related tests(如果你向我们增加一个新的功能, 请添加相关测试).
• Please follow Contributor Covenant Code of Conduct.(请遵循贡献者准则).

[wwbmmm]

LGTM

[yanglimingcn]

请问这个日志名字是怎么定义的，日志会根据大小切分吗

[chenBright]

日志名通过butil::InitLogging LoggingSettings设置

brpc/src/butil/logging.h

Lines 244 to 280 in 2098dd3

	struct BUTIL_EXPORT LoggingSettings {
	// The defaults values are:
	//
	// logging_dest: LOG_DEFAULT
	// log_file: NULL
	// lock_log: LOCK_LOG_FILE
	// delete_old: APPEND_TO_OLD_LOG_FILE
	LoggingSettings();
	LoggingDestination logging_dest;
	// The three settings below have an effect only when LOG_TO_FILE is
	// set in |logging_dest|.
	const LogChar* log_file;
	LogLockingState lock_log;
	OldFileDeletionState delete_old;
	};
	// Implementation of the InitLogging() method declared below.
	BUTIL_EXPORT bool BaseInitLoggingImpl(const LoggingSettings& settings);
	// Sets the log file name and other global logging state. Calling this function
	// is recommended, and is normally done at the beginning of application init.
	// If you don't call it, all the flags will be initialized to their default
	// values, and there is a race condition that may leak a critical section
	// object if two threads try to do the first log at the same time.
	// See the definition of the enums above for descriptions and default values.
	//
	// The default log file is initialized to "<process-name>.log" on linux and
	// "debug.log" otherwise.
	//
	// This function may be called a second time to re-direct logging (e.g after
	// loging in to a user partition), however it should never be called more than
	// twice.
	inline bool InitLogging(const LoggingSettings& settings) {
	return BaseInitLoggingImpl(settings);
	}

[chenBright]

目前框架不支持日志滚动，需要用户自己实现日志滚动逻辑，然后在LoggingLock的保护下更换log_file。

不过，很多日志库都支持日志滚动。框架支持日志滚动特性应该是个合理的需求。

[chenBright]

1. 每次都会消费完所有日志，所以传入IsComplete的肯定是singular node，同时也不需要获取cur_tail。已删除相关逻辑。
2. 进程退出时候，将异步日志队列的日志落盘，并退出异步日志线程。如果在停异步日志线程的时候，有异步日志入队，则有第一个日志所在的线程/协程负责将队列的日志落盘。停止后的异步日志回退为同步日志。为了保证最后的异步日志能全部落盘，在异步日志线程停止（Join结束）后，sleep一小段时间。

[wwbmmm]

LGTM

[chenBright]

当日志打印频率比较低的时候，异步日志有可能退化为每个日志都包含两个动作：signal异步日志线程、异步日志线程落盘。
针对这种场景，采用Socket::Write的策略，同步落盘队头的日志，队列的其他日志通过异步日志线程落盘，减少signal的消耗。对于日志打印频率比较高的场景，可通过开关支持异步日志线程来落盘全部日志。

[wwbmmm]

LGTM