本文共 4193 字，大约阅读时间需要 13 分钟。

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在线程创建和结束时销毁.

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. 假如如果用全局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: 

例子test_TSL.cpp:

#include "stdafx.h"#include 
   
    #include 
    
     #include 
     
      #include 
      
        #include 
       
         #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); }
       
      
     
    
   

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输出:

TestWin32TLSdwTlsIndex 26thread 8452: lpvData=714f50common: thread 8452: lpvData=714f50 : value=8452thread 8460: lpvData=7153d0common: thread 8460: lpvData=7153d0 : value=8460thread 8456: lpvData=715610common: thread 8456: lpvData=715610 : value=8456thread 8464: lpvData=715190common: thread 8464: lpvData=715190 : value=8464TestPthreadTLScommon: thread 8520: lpvData=3b4eb0 : value=8520common: thread 8512: lpvData=3b4ff0 : value=8512common: thread 8516: lpvData=3b4eb0 : value=8516common: thread 8524: lpvData=3b4ff0 : value=8524

参考:

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