PeekNamedPipe 阻塞

（vc++）我用createpipe创建了一个匿名管道，并把读句柄传给子进程。我想在程序中用
PeekNamedPipe(hReadPipe,NULL,NULL,NULL,&tempdword,0);看管道内还有多少字节的信息，结果函数就阻塞在那了。这是为什么

我是这么写的
SECURITY_ATTRIBUTES sa;
sa.nLength=sizeof(SECURITY_ATTRIBUTES);
sa.lpSecurityDescriptor=NULL;
sa.bInheritHandle=true;
CreatePipe(&hReadPipe,&hMyWritePipe,&sa,0);
CreatePipe(&hMyReadPipe,&hWritePipe,&sa,0);
STARTUPINFO si;
PROCESS_INFORMATION pi;
si.cb = sizeof(STARTUPINFO);
GetStartupInfo(&si);
si.hStdOutput = hWritePipe;
si.hStdInput = hReadPipe;
si.wShowWindow = SW_HIDE;
si.dwFlags = STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
CreateProcess((LPSTR)(LPCTSTR)exepath,NULL,NULL,NULL,TRUE,NULL,NULL,NULL,&si,&pi));
在大部分情况下
PeekNamedPipe(hReadPipe,NULL,NULL,NULL,&tempdword,&nextword);

不会阻塞，但是某些情况下就会，不知道为什么？谢谢~

Note ：
The PeekNamedPipe function can block thread execution the same way any I/O function can when called on a synchronous handle in a multi-threaded application.
To avoid this condition, use a pipe handle created forasynchronous I/O.

The PeekNamedPipe() problem on XP only happens when another thread has entered ReadFile() on the read end of the pipe and has not yet returned. Namely, a ReadFile() blocked on the read end of the pipe in one thread will cause any subsequent PeekNamedPipe() in a second thread to also block -- until ReadFile() in the first thread returns.

英语不好，就不翻译出来了。看看对你有没有帮助。

PeekNamedPipe(hReadPipe,NULL,NULL,NULL,&tempdword,&nextword); return tempdword+nextword;