为什么在线程完成之前退出 main() 时，在 C 中的多线程应用程序中会出现访问冲突？

Question

我有一个程序，我创建了 4 个线程，但只等待第一个线程[0]。 线程只是打印一些内容。但是当我执行以下程序时，我会得到访问冲突 有时。

#include<Windows.h>
#include <stdio.h>
#include<tchar.h>

#define KEYLEN 8
#define DATALEN 56
typedef struct _RECORD{
    CHAR key[KEYLEN];
    TCHAR data[DATALEN];        
}RECORD;
#define RECSIZE sizeof(RECORD)
typedef RECORD *LPRECORD;

typedef struct _THREADARG{
    DWORD iTh;
    LPRECORD lowRecord;         // pointer to Low record 
    LPRECORD highRecord;
} THREADARG, *PTHREADARG;

static int KeyCompare(LPCTSTR, LPCTSTR);
static DWORD WINAPI SortThread(PTHREADARG pThArg);
static DWORD nRec;  // Total Number of records to be sorted
static HANDLE *pThreadHandle;


DWORD Options (int argc, LPCTSTR argv [], LPCTSTR OptStr, ...);

int _tmain(int argc, LPTSTR argv[]){
HANDLE hFile, mHandle;
LPRECORD pRecords = NULL;
DWORD lowRecordNum, nRecTh,numFiles, iTh;
LARGE_INTEGER fileSize;
BOOL noPrint;
int iFF, iNP;
PTHREADARG threadArg;
LPTSTR stringEnd;

iNP = 1;
iFF = iNP + 1;
numFiles = _ttoi(argv[iNP]);

if (argc <= iFF)
    _tprintf (_T ("Usage: sortMT [options] nTh files."));

/* Open the file and map it */
hFile = CreateFile (argv[iFF], GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
if (hFile == INVALID_HANDLE_VALUE)
    _tprintf (_T ("Failure to open input file."));

if (!SetFilePointer(hFile, 2, 0, FILE_END) || !SetEndOfFile(hFile))
    _tprintf (_T ("Failure position extend input file."));

mHandle = CreateFileMapping(hFile, NULL, PAGE_READWRITE, 0, 0, NULL);
if (NULL == mHandle)
    _tprintf (_T ("Failure to create mapping handle on input file."));

/* Get the file size. */
if (!GetFileSizeEx (hFile, &fileSize))
    _tprintf (_T ("Error getting file size."));

nRec = (DWORD)fileSize.QuadPart / RECSIZE;  
nRecTh = nRec / numFiles;   
threadArg = malloc (numFiles * sizeof (THREADARG)); /* Array of thread args. */ 
pThreadHandle = malloc (numFiles * sizeof (HANDLE));

/* Map the entire file */
pRecords = MapViewOfFile(mHandle, FILE_MAP_ALL_ACCESS, 0, 0, 0); 
if (NULL == pRecords)
    _tprintf (_T ("Failure to map input file."));
CloseHandle (mHandle);

/* Create the sorting threads. */
lowRecordNum = 0;
for (iTh = 0; iTh < numFiles; iTh++) {
    threadArg[iTh].iTh = iTh;
    threadArg[iTh].lowRecord = pRecords + lowRecordNum;
    threadArg[iTh].highRecord = pRecords + (lowRecordNum + nRecTh);
    lowRecordNum += nRecTh;
    pThreadHandle[iTh] = (HANDLE)_beginthreadex (
        NULL, 0, SortThread, &threadArg[iTh], CREATE_SUSPENDED, NULL);
}

/* Resume all the initially suspened threads. */

for (iTh = 0; iTh < numFiles; iTh++)
    ResumeThread (pThreadHandle[iTh]);


/* Wait for the sort-merge threads to complete. */

WaitForSingleObject (pThreadHandle[0], INFINITE);   
for (iTh = 0; iTh < numFiles; iTh++);
    CloseHandle (pThreadHandle[iTh]);

//Sleep(3);  // Un comment it and see no error.


UnmapViewOfFile(pRecords);
// Restore the file length
/* SetFilePointer is convenient as it's a short addition from the file end */
if (!SetFilePointer(hFile, -2, 0, FILE_END) || !SetEndOfFile(hFile))
    _tprintf("Failure restore input file lenght.");

CloseHandle(hFile);
free (threadArg); free (pThreadHandle);
return 0;
}


DWORD WINAPI SortThread(PTHREADARG pThArg){

DWORD groupSize = 2, myNumber, twoToI = 1;
        /* twoToI = 2^i, where i is the merge step number. */
DWORD_PTR numbersInGroup;
LPRECORD first;

myNumber = pThArg->iTh;
first = pThArg->lowRecord; 
numbersInGroup = (DWORD)(pThArg->highRecord - first); 

printf(" %d : %s \n",myNumber,  pThArg->lowRecord );

return 0;
}

文件内容结构：

02d2d159. Record Number: 00000000.abcdefghijklmnopqrstuvwxyz X
f362711e. Record Number: 00000001.abcdefghijklmnopqrstuvwxyz X
ba957dff. Record Number: 00000002.abcdefghijklmnopqrstuvwxyz X

但是如果我在创建线程之后给一个 Sleep(N); 就没有问题了。！ 所以我理解 main() 线程在子线程之前退出。但是当 main() 退出时，整个进程应该终止。不是吗？ 那么访问冲突怎么可能呢？

为什么我访问冲突？

Answer 1

但是当main()退出时，整个进程应该终止。

最终是的，但是在从main 返回和实际进程终止之间实际上可能有很多代码在运行、破坏进程映像等。

因此，当你...

free (threadArg); free (pThreadHandle);

...还有一个或多个线程尚未完成，将...

printf(" %d : %s \n",myNumber,  pThArg->lowRecord );

...访问例如他们的线程参数pThArg（现已删除）你已经注册了麻烦。

请注意，这只是一个示例。从main 返回后，可能还有更多（内部）共享数据被释放，但仍被线程使用（例如，它们的堆栈，线程句柄......）。

道德：在释放该资源之前等待所有个使用资源的线程终止。

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另外：pThArg->lowRecord 不是char * 所期望的char *，因此你也有未定义的行为。