多線程來減少CPU時間

Question

我想爲需要與來自其他程序和交換數據（接收/發送）的其他線程進行通信的複雜計算進行多線程迭代，我如何使它們進行通信？例如使用文件映射？這會工作嗎？

Answer 1

假設要處理交替，那麼你將需要兩個信號量和每個過程將需要的代碼具有稍微不同序列的呼叫：

方法A：

SemA = CreateAndInitializeSemaphore(); 
SemB = CreateAndInitializeSemaphore(); 

for (i = 0; i < Numpoints; i++) 
{ 
    WaitForSemaphore(SemA); 
    …code for process A… 
    SignalSemaphore(SemB); 
} 

並且類似地對於B除了信號量被逆轉。

for (i = 0; i < Numpoints; i++) 
{ 
    WaitForSemaphore(SemB); 
    …code for process A… 
    SignalSemaphore(SemA); 
} 

請注意，當創建SemA時，需要設置它，以便A能夠立即訪問它。

所有信號函數名稱都需要映射到正確的實際系統調用。

Answer 2

信號量和過程創建需要一些結構。

沒有警告定義是爲了防止使用sscanf或sprintf的警告。 abCmdLine具有進程B（pb.exe）的名稱和共享內存句柄的值。 （注 - 句柄是指針類型）。

循環中有1/2秒的睡眠，所以你可以看看它是如何工作的。在這個例子中，兩個循環同時運行。

更新 - 原始文章被編輯。以前它特別提到了進程A和進程B，以及名爲SemA，SemB的信號量和一個名爲count的計數器。隨着從原始帖子中刪除這些名字，閱讀此主題的人可能會想知道爲什麼這些名字在這裏的例子中被使用。本示例中的其他名稱遵循Microsoft/Windows匈牙利語表示樣式。

#define _CRT_SECURE_NO_WARNINGS 1 
#include <stdio.h> 
#include <windows.h> 

typedef struct SMEM_    /* shared memory offsets */ 
{ 
    HANDLE SemA; 
    HANDLE SemB; 
    int count; 
}SMEM, *PSMEM; 
static HANDLE hMem;    /* handle for shared memory */ 
static PSMEM psMem;    /* ptr to shared memory */ 

/* bInheritHandle = TRUE */ 
static SECURITY_ATTRIBUTES sa = {sizeof(SECURITY_ATTRIBUTES), 
           NULL, TRUE}; 
static STARTUPINFO si = {sizeof(STARTUPINFO), 
         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}; 
/* hProcess = hThread = INVALID_HANDLE_VALUE */ 
static PROCESS_INFORMATION piB = {INVALID_HANDLE_VALUE, 
            INVALID_HANDLE_VALUE, 
            0, 0}; 

int main(int argc, char *argv[]) 
{ 
char abCmdLine[64]; 
    hMem = CreateFileMapping(INVALID_HANDLE_VALUE,&sa,PAGE_READWRITE,0, 
          sizeof(SMEM),NULL); 
    if(hMem == INVALID_HANDLE_VALUE){ 
     goto exit0;} 
    psMem = MapViewOfFile(hMem, FILE_MAP_WRITE, 0, 0, sizeof(SMEM)); 
    if(psMem == NULL){ 
     goto exit0;} 
    memset(psMem, 0, sizeof(SMEM)); 

    /* process A waits before psMem->count++ */ 
    psMem->SemA = CreateSemaphore(&sa,0,2,NULL); 
    if(psMem->SemA == INVALID_HANDLE_VALUE) 
     goto exit0; 
    /* process B waits for count to be updated */ 
    psMem->SemB = CreateSemaphore(&sa,0,2,NULL); 
    if(psMem->SemB == INVALID_HANDLE_VALUE) 
     goto exit0; 
    /* create process B */ 
    sprintf(abCmdLine, "pb.exe %p", hMem); 
    if(0 == CreateProcess(NULL, abCmdLine, NULL, NULL, TRUE, 
      CREATE_NEW_CONSOLE, NULL, NULL, &si, &piB)) 
     goto exit0; 
    for(psMem->count = 0; psMem->count < 20; psMem->count++){ 
     /* allow process B to use psMem->count */ 
     ReleaseSemaphore(psMem->SemB, 1, NULL); 
     printf("%d\n", psMem->count); 
     Sleep(500); 
     /* wait before psMem->count++ */ 
     WaitForSingleObject(psMem->SemA, INFINITE); 
    } 
    /* wait for process B to terminate */ 
    WaitForSingleObject(piB.hProcess, INFINITE); 
exit0: 
    if(piB.hThread != INVALID_HANDLE_VALUE) 
     CloseHandle(piB.hThread); 
    if(piB.hProcess != INVALID_HANDLE_VALUE) 
     CloseHandle(piB.hProcess); 
    if(psMem->SemB != INVALID_HANDLE_VALUE) 
     CloseHandle(psMem->SemB); 
    if(psMem->SemA != INVALID_HANDLE_VALUE) 
     CloseHandle(psMem->SemA); 
    if(hMem != INVALID_HANDLE_VALUE) 
     CloseHandle(hMem); 
    return(0); 
} 

處理B（pb.exe）

#define _CRT_SECURE_NO_WARNINGS 1 
#include <stdio.h> 
#include <windows.h> 

typedef struct SMEM_    /* shared memory offsets */ 
{ 
    HANDLE SemA; 
    HANDLE SemB; 
    int count; 
}SMEM, *PSMEM; 
static HANDLE hMem;    /* handle for shared memory */ 
static PSMEM psMem;    /* ptr to shared memory */ 

int main(int argc, char *argv[]) 
{ 
int done = 0;      /* done flag */ 
    sscanf(argv[1], "%p", &hMem); 
    psMem = MapViewOfFile(hMem, FILE_MAP_WRITE, 0, 0, sizeof(SMEM)); 
    if(psMem == NULL) 
     goto exit0; 
    while(!done){ 
     /* wait for psMem->count to be updated */ 
     WaitForSingleObject(psMem->SemB, INFINITE); 
     printf("%d\n", psMem->count); 
     Sleep(500); 
     done = psMem->count < 19 ? 0 : 1; 
     /* allow process A to update psMem->count */ 
     ReleaseSemaphore(psMem->SemA, 1, NULL); 
    } 
exit0: 
    return(0); 
}