Q151071: FIX: Spawn Hangs When Inheriting Pipe Handle
Article: Q151071
Product(s): Microsoft C Compiler
Version(s): 4.00 4.10
Operating System(s):
Keyword(s): kbCRT kbVC
Last Modified: 30-JUL-2001
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The information in this article applies to:
- The C Run-Time (CRT), included with:
- Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1
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SYMPTOMS
========
When asynchronously spawning a child process that is inheriting a pipe handle,
the parent process hangs before returning from the spawn call.
CAUSE
=====
When you starting Visual C++ version 4.0, the startup code attempts to validate
the inherited handle values by calling GetFileType for each handle. With Windows
NT, if two write handles for the same object are passed to the child process,
the GetFileType hangs when called for the second one.
RESOLUTION
==========
NOTE: In order to use the _pipe function to communicate between a parent and
child process, each process must have only one handle open on the pipe, and each
process must be of opposite sense (the parent has a read handle open, the child
has a write handle open). To implement this behavior, combine the _O_NOINHERIT
flag using the bit-wise-OR operator (|) into the third argument of the _pipe
call. Then, use _dup or _dup2 to create an inheritable copy of the pipe handle
you want to pass to the child. Close the original handle and spawn the child
process. Immediately upon returning from the spawn call in the parent process,
close the duplicate handle.
STATUS
======
Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in Visual C++ 32-bit Edition
version 4.2.
MORE INFORMATION
================
Sample Code
-----------
// Beeper.Cpp
/* Compile options needed: None */
#include <stdio.h>
#include <string.h>
int main()
{
int i;
for (i=0; i<100; ++i)
{
printf("\nThis is speaker beep number %d... \n\7", i+1);
}
return 0;
}
// BeepFilter.Cpp
/* Compile options needed:
Execute as: BeepFilter.exe <path>Beeper.exe
*/
#include <windows.h>
#include <process.h>
#include <memory.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
#define OUT_BUFF_SIZE 512
#define READ_HANDLE 0
#define WRITE_HANDLE 1
#define BEEP_CHAR 7
char szBuffer[OUT_BUFF_SIZE];
int Filter(char* szBuff, ULONG nSize, int nChar)
{
char* szPos = szBuff + nSize -1;
char* szEnd = szPos;
int nRet = nSize;
while (szPos > szBuff)
{
if (*szPos == nChar)
{
memmove(szPos, szPos+1, szEnd - szPos);
--nRet;
}
--szPos;
}
return nRet;
}
int main(int argc, char** argv)
{
int nExitCode = STILL_ACTIVE;
if (argc >= 2)
{
HANDLE hProcess;
int hStdOut;
int hStdOutPipe[2];
// Create the pipe
if(_pipe(hStdOutPipe, 512, O_BINARY | O_NOINHERIT) == -1)
return 1;
// Duplicate stdout handle (next line will close original)
hStdOut = _dup(_fileno(stdout));
// Duplicate write end of pipe to stdout handle
if (_dup2(hStdOutPipe[WRITE_HANDLE], _fileno(stdout)) != 0)
return 2;
// Close original write end of pipe
close(hStdOutPipe[WRITE_HANDLE]);
// Spawn process
hProcess = (HANDLE)spawnvp(P_NOWAIT, argv[1],
(const char* const*)&argv[1]);
// Duplicate copy of original stdout back into stdout
if (_dup2(hStdOut, _fileno(stdout)) != 0)
return 3;
// Close duplicate copy of original stdout
close(hStdOut);
if (hProcess)
{
int nOutRead;
while (nExitCode == STILL_ACTIVE)
{
nOutRead = read(hStdOutPipe[READ_HANDLE],
szBuffer, OUT_BUFF_SIZE);
if (nOutRead)
{
nOutRead = Filter(szBuffer, nOutRead, BEEP_CHAR);
fwrite(szBuffer, 1, nOutRead, stdout);
}
if (!GetExitCodeProcess(hProcess,
(unsigned long*)&nExitCode))
return 4;
}
}
}
printf("\nPress \'ENTER\' key to continue... ");
getchar();
return nExitCode;
}
Additional query words: kbVC400bug 4.00 4.10 4.20 vcfixlist420 CRTIss
======================================================================
Keywords : kbCRT kbVC
Technology : kbVCsearch kbAudDeveloper kbCRT
Version : 4.00 4.10
Issue type : kbbug
Solution Type : kbfix
=============================================================================
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