进程间通信之CreatePipe

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CreatePipe function

创建匿名管道，返回读，写管道的handle。

BOOL WINAPI CreatePipe(
  _Out_     PHANDLE hReadPipe,
  _Out_     PHANDLE hWritePipe,
  _In_opt_  LPSECURITY_ATTRIBUTES lpPipeAttributes,
  _In_      DWORD nSize
);

参数：

hReadPipe [out]
返回对管道读的handle

hWritePipe [out]
返回对管道写的handle

lpPipeAttributes [in, optional]
指向SECURITY_ATTRIBUTES结构的指针。SECURITY_ATTRIBUTES决定了子进程是否可以继承管道的读写handle。
如果lpPipeAttributes是NULL，不能继承。

nSize [in]
管道的缓冲空间。只是一个建议值，系统会根据建议值计算出一个合适的值。如果nSize是0，使用缺省值。

返回值：
如果函数执行成功，返回值非0.
如果失败，返回0。可以通过GetLastError获得更多的信息。

说明：
CreatePipe创建包含适当大小缓冲空间的管道，返回通过ReadFile读， WriteFile写缓冲空间的handle.
ReadFile在如下情况返回：写操作完成，已读到请求大小的字节数，或者发生错误。
WriteFile只到写完所有的字节数才会返回。
若管道缓冲空间在写之前已经满了，那么WriteFile将一直不会返回直到ReadFile读管道后有足够的缓冲空间。
匿名管道是通过命名管道实现的。因此，你可以把匿名管道handle作为命名管道handle使用。
为了释放管道使用的资源，应用程序应该关闭那些不再使用的handles。

下面是子进程的代码。它使用继承的标准输入STDIN和输出STDOUT访问父进程创建的管道。
父进程从in.txt读数据，并把这些数据写到管道1中。子进程从管道1中通过STDIN获得数据，再通过STDOUT写到管道2中。父进程之后再从管道2中读取数据并显示。

//client.cpp

#include <windows.h>
#include <stdio.h>

#define BUFSIZE 4096 
 
int main(void) 
{ 
   CHAR chBuf[BUFSIZE]; 
   DWORD dwRead, dwWritten; 
   HANDLE hStdin, hStdout; 
   BOOL bSuccess; 
 
   hStdout = GetStdHandle(STD_OUTPUT_HANDLE); 
   hStdin = GetStdHandle(STD_INPUT_HANDLE); 
   if ( 
       (hStdout == INVALID_HANDLE_VALUE) || 
       (hStdin == INVALID_HANDLE_VALUE) 
      ) 
      ExitProcess(1); 
 
   // Send something to this process's stdout using printf.
   printf("\n ** This is a message from the child process. ** \n");

   // This simple algorithm uses the existence of the pipes to control execution.
   // It relies on the pipe buffers to ensure that no data is lost.
   // Larger applications would use more advanced process control.

   for (;;) 
   { 
   // Read from standard input and stop on error or no data.
      bSuccess = ReadFile(hStdin, chBuf, BUFSIZE, &dwRead, NULL); 
      
      if (! bSuccess || dwRead == 0) 
         break; 
 
   // Write to standard output and stop on error.
      bSuccess = WriteFile(hStdout, chBuf, dwRead, &dwWritten, NULL); 
      
      if (! bSuccess) 
         break; 
   } 
   return 0;
}

下面的示例展示了如何使用CreateProcess创建子进程。

同时展示了如何通过匿名管道重定向子进程的标准输入和标准输出。

命名管道同样可以用于进程I/O的重定向。

CreatePipe函数使用SECURITY_ATTRIBUTES结构创建可继承的handle。

这些管道指针在STARTUPINFO结构中被指定为子进程的标准输入，输出。

具体的，不妨参考in.txt上的一幅图。

//parent.cpp

#include <windows.h> 
#include <tchar.h>
#include <stdio.h> 
#include <strsafe.h>

#define BUFSIZE 4096 
 
HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;
HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;

HANDLE g_hInputFile = NULL;
 
void CreateChildProcess(void); 
void WriteToPipe(void); 
void ReadFromPipe(void); 
void ErrorExit(PTSTR); 
 
int _tmain(int argc, TCHAR *argv[]) 
{ 
   SECURITY_ATTRIBUTES saAttr; 
 
   printf("\n->Start of parent execution.\n");

// Set the bInheritHandle flag so pipe handles are inherited. 
 
   saAttr.nLength = sizeof(SECURITY_ATTRIBUTES); 
   saAttr.bInheritHandle = TRUE; 
   saAttr.lpSecurityDescriptor = NULL; 

// Create a pipe for the child process's STDOUT.  
   if ( ! CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0) ) 
      ErrorExit(TEXT("StdoutRd CreatePipe")); 

// Ensure the read handle to the pipe for STDOUT is not inherited.
   if ( ! SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0) )
      ErrorExit(TEXT("Stdout SetHandleInformation")); 

// Create a pipe for the child process's STDIN.  
   if (! CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0)) 
      ErrorExit(TEXT("Stdin CreatePipe")); 

// Ensure the write handle to the pipe for STDIN is not inherited.  
   if ( ! SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0) )
      ErrorExit(TEXT("Stdin SetHandleInformation")); 


// Create the child process. 
// g_hChildStd_OUT_Wr and g_hChildStd_IN_Rd will be inherited by child
   
   CreateChildProcess();

// Get a handle to an input file for the parent. 
// This example assumes a plain text file and uses string output to verify data flow. 
 
   if (argc == 1) 
      ErrorExit(TEXT("Please specify an input file.\n")); 

   g_hInputFile = CreateFile(
       argv[1], 
       GENERIC_READ, 
       0, 
       NULL, 
       OPEN_EXISTING, 
       FILE_ATTRIBUTE_READONLY, 
       NULL); 

   if ( g_hInputFile == INVALID_HANDLE_VALUE ) 
      ErrorExit(TEXT("CreateFile")); 
 
// Write to the pipe that is the standard input for a child process. 
// Data is written to the pipe's buffers, so it is not necessary to wait
// until the child process is running before writing data.
 
   WriteToPipe(); 
   printf( "\n->Contents of %s written to child STDIN pipe.\n", argv[1]);
 
// Read from pipe that is the standard output for child process. 
 
   printf( "\n->Contents of child process STDOUT:\n\n", argv[1]);
   ReadFromPipe(); 

   printf("\n->End of parent execution.\n");

// The remaining open handles are cleaned up when this process terminates. 
// To avoid resource leaks in a larger application, close handles explicitly. 

   return 0; 
} 
 
void CreateChildProcess()
// Create a child process that uses the previously created pipes for STDIN and STDOUT.
{ 
   TCHAR szCmdline[]=TEXT("child");
   PROCESS_INFORMATION piProcInfo; 
   STARTUPINFO siStartInfo;
   BOOL bSuccess = FALSE; 
 
// Set up members of the PROCESS_INFORMATION structure. 
 
   ZeroMemory( &piProcInfo, sizeof(PROCESS_INFORMATION) );
 
// Set up members of the STARTUPINFO structure. 
// This structure specifies the STDIN and STDOUT handles for redirection.
 
   ZeroMemory( &siStartInfo, sizeof(STARTUPINFO) );
   siStartInfo.cb = sizeof(STARTUPINFO); 
   siStartInfo.hStdError = g_hChildStd_OUT_Wr;
   siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
   siStartInfo.hStdInput = g_hChildStd_IN_Rd;
   siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
 
// Create the child process. 
    
   bSuccess = CreateProcess(NULL, 
      szCmdline,     // command line 
      NULL,          // process security attributes 
      NULL,          // primary thread security attributes 
      TRUE,          // handles are inherited 
      0,             // creation flags 
      NULL,          // use parent's environment 
      NULL,          // use parent's current directory 
      &siStartInfo,  // STARTUPINFO pointer 
      &piProcInfo);  // receives PROCESS_INFORMATION 
   
   // If an error occurs, exit the application. 
   if ( ! bSuccess ) 
      ErrorExit(TEXT("CreateProcess"));
   else 
   {
      // Close handles to the child process and its primary thread.
      // Some applications might keep these handles to monitor the status
      // of the child process, for example. 

      CloseHandle(piProcInfo.hProcess);
      CloseHandle(piProcInfo.hThread);
   }
}
 
void WriteToPipe(void) 

// Read from a file and write its contents to the pipe for the child's STDIN.
// Stop when there is no more data. 
{ 
   DWORD dwRead, dwWritten; 
   CHAR chBuf[BUFSIZE];
   BOOL bSuccess = FALSE;
 
   for (;;) 
   { 
      bSuccess = ReadFile(g_hInputFile, chBuf, BUFSIZE, &dwRead, NULL);
      if ( ! bSuccess || dwRead == 0 ) break; 
      
      bSuccess = WriteFile(g_hChildStd_IN_Wr, chBuf, dwRead, &dwWritten, NULL);
      if ( ! bSuccess ) break; 
   } 
 
// Close the pipe handle so the child process stops reading. 
 
   if ( ! CloseHandle(g_hChildStd_IN_Wr) ) 
      ErrorExit(TEXT("StdInWr CloseHandle")); 
} 
 
void ReadFromPipe(void) 

// Read output from the child process's pipe for STDOUT
// and write to the parent process's pipe for STDOUT. 
// Stop when there is no more data. 
{ 
   DWORD dwRead, dwWritten; 
   CHAR chBuf[BUFSIZE]; 
   BOOL bSuccess = FALSE;
   HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);

   for (;;) 
   { 
      bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
      if( ! bSuccess || dwRead == 0 ) break; 

      bSuccess = WriteFile(hParentStdOut, chBuf, 
                           dwRead, &dwWritten, NULL);
      if (! bSuccess ) break; 
   } 
} 
 
void ErrorExit(PTSTR lpszFunction) 

// Format a readable error message, display a message box, 
// and exit from the application.
{ 
    LPVOID lpMsgBuf;
    LPVOID lpDisplayBuf;
    DWORD dw = GetLastError(); 

    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | 
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        dw,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR) &lpMsgBuf,
        0, NULL );

    lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT, 
        (lstrlen((LPCTSTR)lpMsgBuf)+lstrlen((LPCTSTR)lpszFunction)+40)*sizeof(TCHAR)); 
    StringCchPrintf((LPTSTR)lpDisplayBuf, 
        LocalSize(lpDisplayBuf) / sizeof(TCHAR),
        TEXT("%s failed with error %d: %s"), 
        lpszFunction, dw, lpMsgBuf); 
    MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK); 

    LocalFree(lpMsgBuf);
    LocalFree(lpDisplayBuf);
    ExitProcess(1);
}

//in.txt

/*Creating a Child Process with Redirected Input and Output
The example in this topic demonstrates how to create a child process 
using the CreateProcess function from a console process. 
It also demonstrates a technique for using anonymous pipes to redirect 
the child process's standard input and output handles. 
Note that named pipes can also be used to redirect process I/O.

  PipServer                     PipClient

g_hChildStd_IN_Wr			g_hChildStd_IN_Rd/STD_INPUT_HANDLE 
		 |-----------------------> 
			  anonymous pipe     
	     <-----------------------|       
g_hChildStd_OUT_Rd			g_hChildStd_OUT_Wr/STD_OUTPUT_HANDLE*/

说明

1, http://msdn.microsoft.com/en-us/library/windows/desktop/aa365152(v=vs.85).aspx

2, http://msdn.microsoft.com/en-us/library/windows/desktop/ms682499(v=vs.85).aspx