pipe.c

C标准库源代码,能提高对C的理解,不错的哦

/***
*pipe.c - create a pipe
*
*       Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       defines _pipe() - creates a pipe (i.e., an I/O channel for interprocess
*                         communication)
*
*******************************************************************************/

#include <cruntime.h>
#include <oscalls.h>
#include <mtdll.h>
#include <io.h>
#include <internal.h>
#include <stdlib.h>
#include <errno.h>
#include <msdos.h>
#include <fcntl.h>

/***
*int _pipe(phandles, psize, textmode) - open a pipe
*
*Purpose:
*       Checks if the given handle is associated with a character device
*       (terminal, console, printer, serial port)
*
*       Multi-thread notes: No locking is performed or deemed necessary. The
*       handles returned by DOSCREATEPIPE are newly opened and, therefore,
*       should not be referenced by any thread until after the _pipe call is
*       complete. The function is not protected from some thread of the caller
*       doing, say, output to a previously invalid handle that becomes one of
*       the pipe handles. However, any such program is doomed anyway and
*       protecting the _pipe function such a case would be of little value.
*
*Entry:
*       int phandle[2] - array to hold returned read (phandle[0]) and write
*                        (phandle[1]) handles
*
*       unsigned psize - amount of memory, in bytes, to ask o.s. to reserve
*                        for the pipe
*
*       int textmode   - _O_TEXT, _O_BINARY, _O_NOINHERIT, or 0 (use default)
*
*Exit:
*       returns 0 if successful
*       returns -1 if an error occurs in which case, errno is set to:
*
*Exceptions:
*
*******************************************************************************/

int __cdecl _pipe (
        int phandles[2],
        unsigned psize,
        int textmode
        )
{
        ULONG dosretval;                    /* o.s. return value */

        HANDLE ReadHandle, WriteHandle;
        SECURITY_ATTRIBUTES SecurityAttributes;

        SecurityAttributes.nLength = sizeof(SecurityAttributes);
        SecurityAttributes.lpSecurityDescriptor = NULL;

        if (textmode & _O_NOINHERIT) {
                SecurityAttributes.bInheritHandle = FALSE;
        }
        else {
                SecurityAttributes.bInheritHandle = TRUE;
        }

        if (!CreatePipe(&ReadHandle, &WriteHandle, &SecurityAttributes, psize)) {
                /* o.s. error */
                dosretval = GetLastError();
                _dosmaperr(dosretval);
                return -1;
        }

        /* now we must allocate C Runtime handles for Read and Write handles */
        if ((phandles[0] = _alloc_osfhnd()) != -1) {

                _osfile(phandles[0]) = (char)(FOPEN | FPIPE | FTEXT);

                if ((phandles[1] = _alloc_osfhnd()) != -1) {

                        _osfile(phandles[1]) = (char)(FOPEN | FPIPE | FTEXT);

                        if ( (textmode & _O_BINARY) ||
                             (((textmode & _O_TEXT) == 0) &&
                              (_fmode == _O_BINARY)) ) {
                                /* binary mode */
                                _osfile(phandles[0]) &= ~FTEXT;
                                _osfile(phandles[1]) &= ~FTEXT;
                        }

                        if ( textmode & _O_NOINHERIT ) {
                                _osfile(phandles[0]) |= FNOINHERIT;
                                _osfile(phandles[1]) |= FNOINHERIT;
                        }

                        _set_osfhnd(phandles[0], (long)ReadHandle);
                        _set_osfhnd(phandles[1], (long)WriteHandle);
                        errno = 0;

                        _unlock_fh(phandles[1]);    /* unlock handle */
                }
                else {
                        _osfile(phandles[0]) = 0;
                        errno = EMFILE;     /* too many files */
                }

                _unlock_fh(phandles[0]);    /* unlock handle */
        }
        else {
                errno = EMFILE;     /* too many files */
        }

        /* If error occurred, close Win32 handles and return -1 */
        if (errno != 0) {
                CloseHandle(ReadHandle);
                CloseHandle(WriteHandle);
                _doserrno = 0;      /* not an o.s. error */
                return -1;
        }

        return 0;
}