glog另启动线程写文本日志

glog本身是很高效的，google的大牛肯定知道大规模的写日志用glog的话肯定会影响业务线程的处理，带负荷的磁盘IO谁都桑不起。比方levelDB就是默认异步写，更不用说google的三驾马车都是分布式的。之前看过其论文，简直是引领时代。

在glog的issue里有人提出了异步写的问题，可是语焉不详，只是0.33版本号已经有了接口，可是还不友好，可是全然能够实现磁盘日志的异步写。

今天算是花了点时间踩了点坑，算是基本能够搞了。稳定之后会把这个版本号和glog，g2log，mudo logging一起測试下。mudo对buffer做了些trick，内部有两个bufferptr，做了双缓冲，据说效率非常高，只是仅仅有linux平台的，只是但把它的log抽离出来也不难，陈老师封装了mutex,thread，conditional等，在gcc4.8,clang3.3,VS2010都不是问题，已经没多大必要，并且之前为之乐道的linux下的threadsafe的initonce,如今C++11x也有了支持。

glog中能够让client定制接口是：

class GOOGLE_GLOG_DLL_DECL Logger {
 public:
  virtual ~Logger();

  // Writes "message[0,message_len-1]" corresponding to an event that
  // occurred at "timestamp".  If "force_flush" is true, the log file
  // is flushed immediately.
  //
  // The input message has already been formatted as deemed
  // appropriate by the higher level logging facility.  For example,
  // textual log messages already contain timestamps, and the
  // file:linenumber header.
  virtual void Write(bool force_flush,
                     time_t timestamp,
                     const char* message,
                     int message_len) = 0;

  // Flush any buffered messages
  virtual void Flush() = 0;

  // Get the current LOG file size.
  // The returned value is approximate since some
  // logged data may not have been flushed to disk yet.
  virtual uint32 LogSize() = 0;

  virtual void SetBasename(const char* basename) = 0;
  virtual void SetExtension(const char* ext) = 0 ;
  virtual void SetSymlinkBasename(const char* symlink_basename) = 0;

};

用Active object模式非常好解决，就是我们通常所说的生产者消费者，在logmsg析构时就会fflush到磁盘，这次就会调用logger的write方法，此时就是我们接手的机会，把数据封装下，投递到业务线程，然后取出，实际写磁盘就好。

封装了简单的Active模式,Activer里封装了LogData用来封装打印实体，Buffer用来线程间传递数据，另外要显式设置Active的回调函数callBack.线程间传递数据用了C++11里的currentQueue,就不须要自己造轮子了：

/** ==========================================================================
* 2010 by KjellKod.cc. This is PUBLIC DOMAIN to use at your own risk and comes
* with no warranties. This code is yours to share, use and modify with no
* strings attached and no restrictions or obligations.
* ============================================================================
*
* Example of a Active Object, using C++11 std::thread mechanisms to make it
* safe for thread communication.
*
* This was originally published at http://sites.google.com/site/kjellhedstrom2/active-object-with-cpp0x
* and inspired from Herb Sutter‘s C++11 Active Object
* http://herbsutter.com/2010/07/12/effective-concurrency-prefer-using-active-objects-instead-of-naked-threads
*
* The code below uses JustSoftware Solutions Inc std::thread implementation
* http://www.justsoftwaresolutions.co.uk
*
* Last update 2012-10-10, by Kjell Hedstrom,
* e-mail: hedstrom at kjellkod dot cc
* linkedin: http://linkedin.com/se/kjellkod */

#ifndef ACTIVE_H_
#define ACTIVE_H_

#include <thread>
#include <functional>
#include <condition_variable>
#include <mutex>
#include <memory>
#include <concurrent_queue.h>
#include "shared_queue.h"

struct  Buffer
{
	Buffer():m_Len(0), m_pMsg(NULL){}
	~Buffer()
	{
		if (NULL != m_pMsg)
			delete []m_pMsg;
	}
	Buffer(int size):m_Len(size)
		, m_pMsg(new char[m_Len])
	{

	}
	int m_Len;
	char* m_pMsg;
};

typedef std::function<void(Buffer*)> Callback;

class Active {
private:
  Active(const Active&); // c++11 feature not yet in vs2010 = delete;
  Active& operator=(const Active&); // c++11 feature not yet in vs2010 = delete;
  Active();                         // Construction ONLY through factory createActive();
  void doDone(){done_ = true;}
  void run();
  void setCallBack(Callback aCallBack);


  Concurrency::concurrent_queue<Buffer*> mq_;
  std::thread thd_;
  bool done_;  // finished flag to be set through msg queue by ~Active
  Callback callBack_;

public:
  virtual ~Active();
  void send(Buffer* apBuffer);
  static std::unique_ptr<Active> createActive(Callback aCallBack); // Factory: safe construction & thread start
};




#endif
/** ==========================================================================
* 2010 by KjellKod.cc. This is PUBLIC DOMAIN to use at your own risk and comes
* with no warranties. This code is yours to share, use and modify with no
* strings attached and no restrictions or obligations.
* ============================================================================
*
* Example of a Active Object, using C++11 std::thread mechanisms to make it
* safe for thread communication.
*
* This was originally published at http://sites.google.com/site/kjellhedstrom2/active-object-with-cpp0x
* and inspired from Herb Sutter‘s C++11 Active Object
* http://herbsutter.com/2010/07/12/effective-concurrency-prefer-using-active-objects-instead-of-naked-threads
*
* The code below uses JustSoftware Solutions Inc std::thread implementation
* http://www.justsoftwaresolutions.co.uk
*
* Last update 2012-10-10, by Kjell Hedstrom,
* e-mail: hedstrom at kjellkod dot cc
* linkedin: http://linkedin.com/se/kjellkod */


#include "active.h"
#include <cassert>

Active::Active(): done_(false){}

Active::~Active() {
  Callback quit_token = std::bind(&Active::doDone, this);
  thd_.join();
}

// Add asynchronously a work-message to queue
void Active::send( Buffer* apBuffer )
{
	if (NULL != apBuffer)
	{
		mq_.push(apBuffer);
	}
}

void Active::run() {
  while (!done_) {
	if (!mq_.empty())
	{
		Buffer* pBuffer = NULL;
		mq_.try_pop(pBuffer);
		if (NULL != pBuffer)
		{
			callBack_(pBuffer);

			delete pBuffer;
		}
	}
  }
}

// Factory: safe construction of object before thread start
std::unique_ptr<Active> Active::createActive(Callback aCallBack){
  std::unique_ptr<Active> aPtr(new Active());
  aPtr->thd_ = std::thread(&Active::run, aPtr.get());
  aPtr->callBack_ = aCallBack;
  return aPtr;
}

void Active::setCallBack( Callback aCallBack )
{
	callBack_ = aCallBack;
}

重点是在threadlogger里，实现了Logger的接口。Write函数实现真正的写逻辑，几个set函数会在内部被调用。

#pragma once
#include <glog/logging.h>
#include <mutex>
#include "active.h"

using namespace std;

namespace google
{

class ThreadLog : public google::base::Logger
{
public:
	ThreadLog();
	~ThreadLog();
	virtual void Write(bool force_flush,
		time_t timestamp,
		const char* message,
		int message_len) ;
	virtual void Flush();
	virtual uint32 LogSize();

	// Configuration options
	void SetBasename(const char* basename);
	void SetExtension(const char* ext);
	void SetSymlinkBasename(const char* symlink_basename);
	void CallBack(Buffer* pBuffer);

private:
	static const uint32 kRolloverAttemptFrequency = 0x20;
	mutex lock_;
	bool base_filename_selected_;
	string base_filename_;
	string symlink_basename_;
	string filename_extension_;     // option users can specify (eg to add port#)
	FILE* file_;
	LogSeverity severity_;
	uint32 bytes_since_flush_;
	uint32 file_length_;
	unsigned int rollover_attempt_;
	int64 next_flush_time_;         // cycle count at which to flush log
	string hostname;
	bool stopWriting;
	std::unique_ptr<Active> m_pActive;
	bool CreateLogfile(const string& time_pid_string);
	void FlushUnlocked();
	void WriteInteral(bool force_flush, time_t timestamp, const char* message, int message_len);
};

}

#include "ThreadLog.h"
#include "port.h"
#include <fcntl.h>
#include <iomanip> 
#include "utilities.h"
#include <functional>

namespace google
{
	static int GetSize(bool& force_flush, time_t& timestamp, const char* message, int& message_len)
	{
		return sizeof(force_flush)+sizeof(timestamp)+sizeof(message_len)+message_len;
	}

	void ThreadLog::Write( bool force_flush, time_t timestamp, const char* message, int message_len )
	{
		Buffer* pBuffer = new Buffer(GetSize(force_flush, timestamp, message, message_len));
		char* curData = pBuffer->m_pMsg;
		memcpy(curData, &force_flush, sizeof(force_flush));
		curData += sizeof(force_flush);

		memcpy(curData, ×tamp, sizeof(timestamp));
		curData += sizeof(timestamp);

		memcpy(curData, &message_len, sizeof(message_len));
		curData += sizeof(message_len);

		memcpy(curData, message, message_len);
		curData += message_len;

		m_pActive->send(pBuffer);
	}

	void ThreadLog::Flush()
	{

	}

	google::uint32 ThreadLog::LogSize()
	{
		return 0;
	}

	void ThreadLog::SetBasename( const char* basename )
	{
		std::lock_guard<std::mutex> lock(lock_);
		base_filename_selected_ = true;
		if (base_filename_ != basename) 
		{
			if (file_ != NULL) 
			{
				fclose(file_);
				file_ = NULL;
				rollover_attempt_ = kRolloverAttemptFrequency-1;
			}
			base_filename_ = basename;
		}
	}

	void ThreadLog::SetExtension( const char* ext )
	{
		std::lock_guard<std::mutex> lock(lock_);
		if (filename_extension_ != ext) 
		{
			// Get rid of old log file since we are changing names
			if (file_ != NULL) 
			{
				fclose(file_);
				file_ = NULL;
				rollover_attempt_ = kRolloverAttemptFrequency-1;
			}
			filename_extension_ = ext;
		}
	}

	void ThreadLog::SetSymlinkBasename( const char* symlink_basename )
	{
		std::lock_guard<std::mutex> lock(lock_);
		symlink_basename_ = symlink_basename;
	}

	bool ThreadLog::CreateLogfile( const string& time_pid_string )
	{
		string string_filename = base_filename_+filename_extension_+
			time_pid_string;
		const char* filename = string_filename.c_str();
		int fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0664);
		if (fd == -1) return false;
#ifdef HAVE_FCNTL
		// Mark the file close-on-exec. We don‘t really care if this fails
		fcntl(fd, F_SETFD, FD_CLOEXEC);
#endif

		file_ = fdopen(fd, "a");  // Make a FILE*.
		if (file_ == NULL) {  // Man, we‘re screwed!
			close(fd);
			unlink(filename);  // Erase the half-baked evidence: an unusable log file
			return false;
		}

		if (!symlink_basename_.empty()) {
			// take directory from filename
			const char* slash = strrchr(filename, ‘/‘);
			const string linkname =
				symlink_basename_ + ‘.‘ + LogSeverityNames[severity_];
			string linkpath;
			if ( slash ) linkpath = string(filename, slash-filename+1);  // get dirname
			linkpath += linkname;
			unlink(linkpath.c_str());                    // delete old one if it exists

			// We must have unistd.h.
#ifdef HAVE_UNISTD_H
			// Make the symlink be relative (in the same dir) so that if the
			// entire log directory gets relocated the link is still valid.
			const char *linkdest = slash ? (slash + 1) : filename;
			if (symlink(linkdest, linkpath.c_str()) != 0) {
				// silently ignore failures
			}

			// Make an additional link to the log file in a place specified by
			// FLAGS_log_link, if indicated
			if (!FLAGS_log_link.empty()) {
				linkpath = FLAGS_log_link + "/" + linkname;
				unlink(linkpath.c_str());                  // delete old one if it exists
				if (symlink(filename, linkpath.c_str()) != 0) {
					// silently ignore failures
				}
			}
#endif
		}

		return true;  // Everything worked
	}

	void ThreadLog::FlushUnlocked()
	{
		if (file_ != NULL) 
		{
			fflush(file_);
			bytes_since_flush_ = 0;
		}

		const int64 next = (FLAGS_logbufsecs * static_cast<int64>(1000000));  // in usec
		next_flush_time_ = CycleClock_Now() + UsecToCycles(next);
	}

	ThreadLog::ThreadLog(): file_(NULL)
		, bytes_since_flush_(0)
		, file_length_(0)
		, rollover_attempt_(0)
		, next_flush_time_(0)
		, stopWriting(false)
		, m_pActive(Active::createActive(std::bind(&ThreadLog::CallBack, this, std::placeholders::_1)))
	{
	}

	ThreadLog::~ThreadLog()
	{

	}

	void ThreadLog::WriteInteral( bool force_flush, time_t timestamp, const char* message, int message_len )
	{
		if (base_filename_selected_ && base_filename_.empty())
		{
			return;
		}

		if (static_cast<int>(file_length_ >> 20) >= MaxLogSize()) 
		{
			if (file_ != NULL) 
				fclose(file_);
			file_ = NULL;
			file_length_ = bytes_since_flush_ = 0;
			rollover_attempt_ = kRolloverAttemptFrequency-1;
		}

		if (file_ == NULL) 
		{
			//if (++rollover_attempt_ != kRolloverAttemptFrequency) 
			//	return;
			//rollover_attempt_ = 0;

			struct ::tm tm_time;
			localtime_r(×tamp, &tm_time);
			ostringstream time_pid_stream;
			time_pid_stream.fill(‘0‘);
			time_pid_stream << 1900+tm_time.tm_year
				<< setw(2) << 1+tm_time.tm_mon
				<< setw(2) << tm_time.tm_mday
				<< ‘-‘
				<< setw(2) << tm_time.tm_hour
				<< setw(2) << tm_time.tm_min
				<< setw(2) << tm_time.tm_sec
				<< ‘.‘
				<< GetCurrentThreadId();
			const string& time_pid_string = time_pid_stream.str();

			if (base_filename_selected_) 
			{
				if (!CreateLogfile(time_pid_string)) 
				{
					perror("Could not create log file");
					fprintf(stderr, "COULD NOT CREATE LOGFILE ‘%s‘!\n", time_pid_string.c_str());
					return;
				}
			} 
			else 
			{
				string stripped_filename(glog_internal_namespace_::ProgramInvocationShortName());
				GetHostName(&hostname);
				string uidname = MyUserName();
				if (uidname.empty()) 
					uidname = "invalid-user";

				stripped_filename = stripped_filename+‘.‘+hostname+‘.‘+uidname+".log."+LogSeverityNames[severity_]+‘.‘;
				const vector<string> & log_dirs = GetLoggingDirectories();

				bool success = false;
				for (vector<string>::const_iterator dir = log_dirs.begin();dir != log_dirs.end(); ++dir) 
				{
						base_filename_ = *dir + "/" + stripped_filename;
						if ( CreateLogfile(time_pid_string) ) 
						{
							success = true;
							break;
						}
				}

				if ( success == false ) 
				{
					perror("Could not create logging file");
					fprintf(stderr, "COULD NOT CREATE A LOGGINGFILE %s!",
						time_pid_string.c_str());
					return;
				}
			}

			ostringstream file_header_stream;
			file_header_stream.fill(‘0‘);
			file_header_stream << "Log file created at: "
				<< 1900+tm_time.tm_year << ‘/‘
				<< setw(2) << 1+tm_time.tm_mon << ‘/‘
				<< setw(2) << tm_time.tm_mday
				<< ‘ ‘
				<< setw(2) << tm_time.tm_hour << ‘:‘
				<< setw(2) << tm_time.tm_min << ‘:‘
				<< setw(2) << tm_time.tm_sec << ‘\n‘
				<< "Running on machine: "
				<< hostname << ‘\n‘
				<< "Log line format: [IWEF]mmdd hh:mm:ss.uuuuuu "
				<< "threadid file:line] msg" << ‘\n‘;
			const string& file_header_string = file_header_stream.str();

			const int header_len = file_header_string.size();
			fwrite(file_header_string.data(), 1, header_len, file_);
			file_length_ += header_len;
			bytes_since_flush_ += header_len;
		}

		if ( !stopWriting ) 
		{
			errno = 0;
			fwrite(message, 1, message_len, file_);
			if ( FLAGS_stop_logging_if_full_disk && errno == ENOSPC ) 
			{  // disk full, stop writing to disk
				stopWriting = true;  // until the disk is
				return;
			} 
			else 
			{
				file_length_ += message_len;
				bytes_since_flush_ += message_len;
			}
		} 
		else 
		{
			if ( CycleClock_Now() >= next_flush_time_ )
				stopWriting = true;  // check to see if disk has free space.
		}

		if ( force_flush || (bytes_since_flush_ >= 1000000) || (CycleClock_Now() >= next_flush_time_) ) {
				FlushUnlocked();
#ifdef OS_LINUX
				if (FLAGS_drop_log_memory) {
					if (file_length_ >= logging::kPageSize) {
						// don‘t evict the most recent page
						uint32 len = file_length_ & ~(logging::kPageSize - 1);
						posix_fadvise(fileno(file_), 0, len, POSIX_FADV_DONTNEED);
					}
				}
#endif
		}
	}

	void ThreadLog::CallBack( Buffer* pBuffer )
	{
		char* curData = pBuffer->m_pMsg;
		bool force_flush = *(bool*)curData;
		curData += sizeof(force_flush);
		time_t timestamp = *(time_t*)curData;
		curData += sizeof(timestamp);
		int message_len = *(int*)curData;
		curData += sizeof(message_len);
		char* message = curData;
		WriteInteral(force_flush, timestamp, message, message_len);
	}

}

#define GLOG_NO_ABBREVIATED_SEVERITIES
#include <windows.h>
#include <glog/logging.h>
#include "ThreadLog.h"

using namespace google;
int main(int argc, char* argv[]) {
	google::InitGoogleLogging("test/testsss");
	google::base::Logger* mylogger = new google::ThreadLog;
	SetLogger(google::GLOG_INFO, mylogger);

	google::SetLogDestination(google::GLOG_INFO, "../Debug/logtestInfo"); 
	//google::SetLogDestination(google::GLOG_ERROR, "../Debug/logtestDebug");

	int num_cookies = 0;

	google::SetStderrLogging(google::GLOG_INFO);
	//google::SetStderrLogging(google::GLOG_ERROR);
	//google::LogToStderr();
	for (int i = 0; i < 1000; ++i){
		LOG(INFO) << "how are " << i << " cookies";
	}

	google::ShutdownGoogleLogging();
}

整个项目地址：git@github.com:boyxiaolong/Proejcts.git

測试还有点问题，偶尔会有乱码，并且须要优化的是那个Buffer的动态申请。

只是都是后话了。