[并发并行]_[C/C++]_[使用线程本地存储Thread Local Storage(TLS)-win32和pthread比较]

场景:

1.  需要统计某个线程的对象上创建的个数.

2. 当创建的堆空间需要根据线程需要创建和结束时销毁时.

3. 因为范围是线程只能看到自己的存储数据，所以不需要临界区或互斥量来维护自己的堆内存. 加入如果用全局std::map实现,那么必须在put和get时加锁，这是很损耗资源的.

4. 可以用在维护一个连接，比如socket,database连接.

说明:

1. Java也有自己的线程本地存储ThreadLocal

2. pthread的win32版本: http://sourceware.org/pthreads-win32/

例子test_TSL.cpp:

#include "stdafx.h"
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <assert.h>
#include <windows.h>
#include "pthread.h"

#define THREADCOUNT 4
DWORD dwTlsIndex;
VOID ErrorExit(const char*); 

static pthread_barrier_t barrier  = NULL;
static pthread_once_t random_is_initialized = PTHREAD_ONCE_INIT;
static pthread_key_t key;

VOID CommonFunc(VOID)
{
   LPVOID lpvData; 

// Retrieve a data pointer for the current thread. 

   lpvData = TlsGetValue(dwTlsIndex);
   if ((lpvData == 0) && (GetLastError() != ERROR_SUCCESS))
      ErrorExit("TlsGetValue error"); 

// Use the data stored for the current thread.
   int64_t* value = (int64_t*)lpvData;
   printf("common: thread %d: lpvData=%lx : value=%lld\n",
      GetCurrentThreadId(), lpvData,*value); 

   Sleep(5000);
} 

DWORD WINAPI ThreadFunc(VOID)
{
   LPVOID lpvData; 

// Initialize the TLS index for this thread. 

   lpvData = (LPVOID) LocalAlloc(LPTR, 8);
   if (! TlsSetValue(dwTlsIndex, lpvData))
      ErrorExit("TlsSetValue error"); 

   int64_t* value = (int64_t*)lpvData;
   *value = GetCurrentThreadId();
   printf("thread %d: lpvData=%lx\n", GetCurrentThreadId(), lpvData); 

   CommonFunc(); 

// Release the dynamic memory before the thread returns. 

   lpvData = TlsGetValue(dwTlsIndex);
   if (lpvData != 0)
      LocalFree((HLOCAL) lpvData); 

   return 0;
}

void TestWin32TLS()
{
   DWORD IDThread;
   HANDLE hThread[THREADCOUNT];
   int i; 

// Allocate a TLS index. 

   if ((dwTlsIndex = TlsAlloc()) == TLS_OUT_OF_INDEXES)
      ErrorExit("TlsAlloc failed");

   //1. 注意,这个dwTlsIndex 并不是从0开始.
   printf("dwTlsIndex %ld\n",dwTlsIndex);
// Create multiple threads. 

   for (i = 0; i < THREADCOUNT; i++)
   {
      hThread[i] = CreateThread(NULL, // default security attributes
         0,                           // use default stack size
         (LPTHREAD_START_ROUTINE) ThreadFunc, // thread function
         NULL,                    // no thread function argument
         0,                       // use default creation flags
         &IDThread);              // returns thread identifier 

   // Check the return value for success.
      if (hThread[i] == NULL)
         ErrorExit("CreateThread error\n");
   } 

   for (i = 0; i < THREADCOUNT; i++)
      WaitForSingleObject(hThread[i], INFINITE); 

   TlsFree(dwTlsIndex);
}

void CommonFuncPthread(void)
{
   void* lpvData = pthread_getspecific(key);
   int64_t* value = (int64_t*)lpvData;
   printf("common: thread %d: lpvData=%lx : value=%lld\n",
      GetCurrentThreadId(), lpvData,*value);
}

void* StartPthread(void* data)
{
	int64_t *buf = (int64_t*)malloc(256);
	*buf = GetCurrentThreadId();
	pthread_setspecific(key, buf);
	CommonFuncPthread();
	free(buf);
    pthread_barrier_wait(&barrier);

	return NULL;
}

//1.只调用一次,可以放在随意一个work thread执行函数里都可以,会随机找一个线程执行.
//2.类似win32的DLL_PROCESS_ATTACH只执行一次.

void TestPthreadTLS()
{
	pthread_key_create(&key, NULL);
	pthread_barrier_init(&barrier,NULL, THREADCOUNT + 1);
	for(int i = 0; i< THREADCOUNT; ++i)
	{
		pthread_t t;
		pthread_create(&t,NULL,StartPthread,NULL);
		pthread_detach(t);
	}
	//1.等待其他线程执行完.
	pthread_barrier_wait(&barrier);
	pthread_key_delete(key);
}

DWORD main(VOID)
{
   //1.win32TLS
   printf("TestWin32TLS\n");
   TestWin32TLS();
   //1.pthread TLS
   printf("TestPthreadTLS\n");
   TestPthreadTLS();
   return 0;
} 

VOID ErrorExit (const char* lpszMessage)
{
   fprintf(stderr, "%s\n", lpszMessage);
   ExitProcess(0);
}

.

输出:

TestWin32TLS
dwTlsIndex 26
thread 8452: lpvData=714f50
common: thread 8452: lpvData=714f50 : value=8452
thread 8460: lpvData=7153d0
common: thread 8460: lpvData=7153d0 : value=8460
thread 8456: lpvData=715610
common: thread 8456: lpvData=715610 : value=8456
thread 8464: lpvData=715190
common: thread 8464: lpvData=715190 : value=8464
TestPthreadTLS
common: thread 8520: lpvData=3b4eb0 : value=8520
common: thread 8512: lpvData=3b4ff0 : value=8512
common: thread 8516: lpvData=3b4eb0 : value=8516
common: thread 8524: lpvData=3b4ff0 : value=8524

参考:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms686749(v=vs.85).aspx

https://msdn.microsoft.com/en-us/library/windows/desktop/ms686991(v=vs.85).aspx

http://blog.chinaunix.net/uid-10231348-id-3034751.html

http://blog.csdn.net/liulina603/article/details/17991731

http://linux.die.net/man/3/pthread_once