（七）
经过短暂的熟悉过程，log4cplus已经被成功应用到了我的项目中去了，效果还不错，：）除了上文提及的功能之外，下面将介绍log4cplus提供的线程和套接字的使用情况。
### NDC ###
首先我们先了解一下log4cplus中嵌入诊断上下文（Nested Diagnostic Context），即NDC。对log系统而言，当输入源可能不止一个，而只有一个输出时，往往需要分辩所要输出消息的来源，比如服务器处理来自不同客户端的消息时就需要作此判断，NDC可以为交错显示的信息打上一个标记(stamp)， 使得辨认工作看起来比较容易些，呵呵。这个标记是线程特有的，利用了线程局部存储机制，称为线程私有数据（Thread-specific Data，或TSD）。 看了一下源代码，相关定义如下，包括定义、初始化、获取、设置和清除操作：
linux pthread
# define LOG4CPLUS_THREAD_LOCAL_TYPE pthread_key_t*
#define LOG4CPLUS_THREAD_LOCAL_INIT ::log4cplus::thread::createPthreadKey()
# define LOG4CPLUS_GET_THREAD_LOCAL_VALUE( key ) pthread_getspecific(*key)
#define LOG4CPLUS_SET_THREAD_LOCAL_VALUE( key, value ) pthread_setspecific(*key, value)
# define LOG4CPLUS_THREAD_LOCAL_CLEANUP( key ) pthread_key_delete(*key)win32
#define LOG4CPLUS_THREAD_LOCAL_TYPE DWORD
#define LOG4CPLUS_THREAD_LOCAL_INIT TlsAlloc()
# define LOG4CPLUS_GET_THREAD_LOCAL_VALUE( key ) TlsGetValue(key)
#define LOG4CPLUS_SET_THREAD_LOCAL_VALUE( key, value ) \
TlsSetValue(key, static_cast<lpvoid></lpvoid>(value))
#define LOG4CPLUS_THREAD_LOCAL_CLEANUP( key ) TlsFree(key)
使用起来比较简单，在某个线程中：
NDC& ndc = log4cplus::getNDC();
ndc.push("ur ndc string");
LOG4CPLUS_DEBUG(logger, "this is a NDC test");
... ...
ndc.pop();
... ...
LOG4CPLUS_DEBUG(logger, "There should be no NDC...");
ndc.remove();
当设定输出格式(Layout)为TTCCLayout时，输出如下：
10-21-04 21:32:58, [3392] DEBUG test <ur string="" ndc=""></ur> - this is a NDC test
10-21-04 21:32:58, [3392] DEBUG test <> - There should be no NDC...
也可以在自定义的输出格式中使用NDC(用%x) ，比如：
... ...
std::string pattern = "NDC:[%x] - %m %n";
std::auto_ptr<Layout>_layout(new PatternLayout(pattern));
... ...
LOG4CPLUS_DEBUG(_logger, "This is the FIRST log message...")
NDC& ndc = log4cplus::getNDC();
ndc.push("ur ndc string");
LOG4CPLUS_WARN(_logger, "This is the SECOND log message...")
ndc.pop();
ndc.remove();
... ...
输出如下：
NDC:[] - This is the FIRST log message...
NDC:[ur ndc string] - This is the SECOND log message...
另外一种更简单的使用方法是在线程中直接用NDCContextCreator：
NDCContextCreator _first_ndc("ur ndc string");
LOG4CPLUS_DEBUG(logger, "this is a NDC test")
不必显式地调用push/pop了，而且当出现异常时，能够确保push与pop的调用是匹配的。
### 线程 ###
线程是log4cplus中的副产品， 而且仅作了最基本的实现，使用起来也异常简单，只要且必须要在派生类中重载run函数即可：
class TestThread : public AbstractThread
{
public:
virtual void run();
};
void TestThread::run()
{
/* do sth. */
... ...
}
log4cplus的线程没有考虑同步、死锁，有互斥，实现线程切换的小函数挺别致的：
void log4cplus::thread::yield()
{
#if defined(LOG4CPLUS_USE_PTHREADS)
::sched_yield();
#elif defined(LOG4CPLUS_USE_WIN32_THREADS)
::Sleep(0);
#endif
}
### 套接字 ###
套接字也是log4cplus中的副产品，在namespace log4cplus::helpers中，实现了C/S方式的日志记录。
1. 客户端程序需要做的工作：
/* 定义一个SocketAppender类型的挂接器 */
SharedAppenderPtr _append(new SocketAppender(host, 8888, "ServerName"));
/* 把_append加入到logger中 */
Logger::getRoot().addAppender(_append);
/* SocketAppender类型不需要Layout, 直接调用宏就可以将信息发往loggerServer了*/
LOG4CPLUS_INFO(Logger::getRoot(), "This is a test: ")
【注】 这里对宏的调用其实是调用了SocketAppender::append，里面有一个数据传输约定，即先发送一个后续数据的总长度，然后再发送实际的数据：
... ...
SocketBuffer buffer = convertToBuffer(event, serverName);
SocketBuffer msgBuffer(LOG4CPLUS_MAX_MESSAGE_SIZE);
msgBuffer.appendSize_t(buffer.getSize());
msgBuffer.appendBuffer(buffer);
... ...
2. 服务器端程序需要做的工作：
/* 定义一个ServerSocket */
ServerSocket serverSocket(port);
/* 调用accept函数创建一个新的socket与客户端连接 */
Socket sock = serverSocket.accept();
此后即可用该sock进行数据read/write了,形如：
SocketBuffer msgSizeBuffer(sizeof(unsigned int));
if(!clientsock.read(msgSizeBuffer))
{
return;
}
unsigned int msgSize = msgSizeBuffer.readInt();
SocketBuffer buffer(msgSize);
if(!clientsock.read(buffer)){
return;
}
为了将读到的数据正常显示出来，需要将SocketBuffer存放的内容转换成InternalLoggingEvent格式：
spi::InternalLoggingEvent event = readFromBuffer(buffer);
然后输出：
Logger logger = Logger::getInstance(event.getLoggerName());
logger.callAppenders(event);
【注】 read/write是按照阻塞方式实现的，意味着对其调用直到满足了所接收或发送的个数才返回。
log4cplus的三个例程 http://log4cplus.sourceforge.net/codeexamples.html 里面自带的三个例程
Hello World Example
#include <log4cplus\logger.h>
#include <log4cplus\configurator.h>
#include <iomanip>
using namespace log4cplus;
intmain()
{
BasicConfigurator config;
config.configure();
Logger logger = Logger::getInstance("main");
LOG4CPLUS_WARN(logger, "Hello, World!");
return 0;
}
ostream Example (Show how to write logging messages.)
#include <log4cplus\logger.h>
#include <log4cplus\configurator.h>
#include <iomanip>
using namespace std;
using namespace log4cplus;
intmain()
{
BasicConfigurator config;
config.configure();
Logger logger = Logger::getInstance("logger");
LOG4CPLUS_WARN(logger, "This is"
<< " a reall"
<< "y long message." << endl
<< "Just testing it out" << endl
<< "What do you think?")
LOG4CPLUS_WARN(logger, "This is a bool: " << true)
LOG4CPLUS_WARN(logger, "This is a char: " << 'x')
LOG4CPLUS_WARN(logger, "This is a short: " << (short)-100)
LOG4CPLUS_WARN(logger, "This is a unsigned short: " << (unsigned short)100)
LOG4CPLUS_WARN(logger, "This is a int: " << (int)1000)
LOG4CPLUS_WARN(logger, "This is a unsigned int: " << (unsigned int)1000)
LOG4CPLUS_WARN(logger, "This is a long(hex): " << hex << (long)100000000)
LOG4CPLUS_WARN(logger, "This is a unsigned long: "
<< (unsigned long)100000000)
LOG4CPLUS_WARN(logger, "This is a float: " << (float)1.2345)
LOG4CPLUS_WARN(logger, "This is a double: "
<< setprecision(15)
<< (double)1.2345234234)
LOG4CPLUS_WARN(logger, "This is a long double: "
<< setprecision(15)
<< (long double)123452342342.342)
return 0;
}
LogLevel Example (Shows how log messages can be filtered at runtime by adjusting the LogLevel.)
#include <log4cplus\logger.h>
#include <log4cplus\configurator.h>
#include <iostream>
using namespace std;
using namespace log4cplus;
Logger logger = Logger::getInstance("main");
void printMessages()
{
LOG4CPLUS_TRACE(logger, "printMessages()");
LOG4CPLUS_DEBUG(logger, "This is a DEBUG message");
LOG4CPLUS_INFO(logger, "This is a INFO message");
LOG4CPLUS_WARN(logger, "This is a WARN message");
LOG4CPLUS_ERROR(logger, "This is a ERROR message");
LOG4CPLUS_FATAL(logger, "This is a FATAL message");}
intmain()
{
BasicConfigurator config;
config.configure();
logger.setLogLevel(TRACE_LOG_LEVEL);
cout << "*** calling printMessages() with TRACE set: ***" << endl;
printMessages();
logger.setLogLevel(DEBUG_LOG_LEVEL);
cout << "\n*** calling printMessages() with DEBUG set: ***" << endl;
printMessages();
logger.setLogLevel(INFO_LOG_LEVEL);
cout << "\n*** calling printMessages() with INFO set: ***" << endl;
printMessages();
logger.setLogLevel(WARN_LOG_LEVEL);
cout << "\n*** calling printMessages() with WARN set: ***" << endl;
printMessages();
logger.setLogLevel(ERROR_LOG_LEVEL);
cout << "\n*** calling printMessages() with ERROR set: ***" << endl;
printMessages();
logger.setLogLevel(FATAL_LOG_LEVEL);
cout << "\n*** calling printMessages() with FATAL set: ***" << endl;
printMessages();
return 0;
}
