盡量少使用全局變量和靜態變量，盡量用棧上變量，也可用動態TLS和靜態TLS

數據與對象實例關聯起來
如SetWindowWord / SetWindowLong 將數據與窗口關聯起來

進程中每個線程都有TLS_MINIMUM_AVAILABLE個PVOID值的數組，一旦一個線程預訂了一個索引，進程內所有正在運行或將創建的線程都不能再使用這個索引

DWORD TlsAlloc();
TlsSetValue
TlsGetValue
TlsFree(DWORD index);

對DLL使用TLS，TlsAlloc放在DLL_PROCESS_ATTACH，TlsFree放在DLL_PROCESS_DETACH。 而index作為全局變量，但index不能其他用處會涉及多線程問題。

// dll project

// testdll.h

#ifdef TESTDLL_EXPORTS
#define TESTDLL_API __declspec(dllexport)
#else
#define TESTDLL_API __declspec(dllimport)
#endif
#include <Windows.h>

typedef struct _SomeStruct{
?DWORD index;
?DWORD tid;
?char buf[256];
}SomeStruct,*PSomeStruct;

TESTDLL_API PSomeStruct Fun(PSomeStruct pSomeStruct);

//testdll.cpp

#include "testdll.h"
#include <iostream>
#include <Windows.h>

DWORD g_dwTlsIndex;
BOOL APIENTRY DllMain( HMODULE hModule,
?????????????????????? DWORD? ul_reason_for_call,
?????????????????????? LPVOID lpReserved
????? )
{
?switch (ul_reason_for_call)
?{
?case DLL_PROCESS_ATTACH:
??{
???g_dwTlsIndex = TlsAlloc();
???std::cout << "case DLL_PROCESS_ATTACH: TlsAlloc:" << g_dwTlsIndex << std::endl;
??}
??break;
?case DLL_THREAD_ATTACH:
??break;
?case DLL_THREAD_DETACH:
??break;
?case DLL_PROCESS_DETACH:
??{
???TlsFree(g_dwTlsIndex);
???std::cout << "case DLL_PROCESS_DETACH: TlsFree:" << g_dwTlsIndex << std::endl;
??}
??break;
?}
?return TRUE;
}

TESTDLL_API PSomeStruct Fun(PSomeStruct pSomeStruct)
{
?if( pSomeStruct != NULL )
?{
??pSomeStruct->index = g_dwTlsIndex;
??if( TlsGetValue(g_dwTlsIndex) == NULL )
??{
???TlsSetValue(g_dwTlsIndex,HeapAlloc(GetProcessHeap(),0,sizeof(*pSomeStruct)));
??}
??memcpy(TlsGetValue(g_dwTlsIndex),pSomeStruct,sizeof(*pSomeStruct));
??return NULL;
?}
?else
?{
??return (PSomeStruct)TlsGetValue(g_dwTlsIndex);
?}
}

?

//test project

//main.cpp

#include <Windows.h>
#include "testdll\testdll.h"
#include <iostream>
#include <process.h>

unsigned __stdcall SecondThreadFunc( void* pArguments )

{
?DWORD tid = GetCurrentThreadId();
?SomeStruct ss = {0,tid,""};
?memcpy(ss.buf,pArguments,strlen((const char*)pArguments));
?
?Fun(&ss);

?while(true)
?{
??PSomeStruct pget =Fun(NULL);
??std::cout << "tlsindex:" << pget->index << "? tid:" << tid << "? buf:" << pget->buf << std::endl;
??Sleep(2000);
?}

?_endthreadex( 0 );
??? return 0;
}

int wmain(int argc, wchar_t* argv[])
{
?DWORD tid = GetCurrentThreadId();
?SomeStruct ss = {0,tid,"11111111"};
?Fun(&ss);
?PSomeStruct pget =Fun(NULL);
?std::cout << "tlsindex:" << pget->index << "? tid:" << tid << "? buf:" << pget->buf << std::endl;
?
?HANDLE hThread1,hThread2;
??? unsigned threadID;
?char *str1 = "first thread value";
?char *str2 = "second thread value";
?hThread1 = (HANDLE)_beginthreadex( NULL, 0, SecondThreadFunc, str1, 0, &threadID );
?hThread2 = (HANDLE)_beginthreadex( NULL, 0, SecondThreadFunc, str2, 0, &threadID );

?WaitForSingleObject( hThread1, INFINITE );
?WaitForSingleObject( hThread2, INFINITE );

?CloseHandle( hThread1 );
?CloseHandle( hThread2 );
?return 0;
}

?

//test result:

?

note: TLS 不要用多個索引存放一個數組，不如一個索引存放一個數組指針。

?

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