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Tricks of the Windows Gam…ming Gurus (2nd Edition)
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Disc2.iso
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vc98
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crt
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src
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popen.c
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C/C++ Source or Header
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1998-06-17
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530 lines
/***
*popen.c - initiate a pipe and a child command
*
* Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
* Defines _popen() and _pclose().
*
*******************************************************************************/
#include <cruntime.h>
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <process.h>
#include <io.h>
#include <fcntl.h>
#include <internal.h>
#include <errno.h>
#include <msdos.h>
#include <mtdll.h>
#include <oscalls.h>
#include <tchar.h>
#include <dbgint.h>
/* size for pipe buffer
*/
#define PSIZE 1024
#define STDIN 0
#define STDOUT 1
/* definitions for table of stream pointer - process handle pairs. the table
* is created, maintained and accessed by the idtab function. _popen and
* _pclose gain access to table entries only by calling idtab. Note that the
* table is expanded as necessary (by idtab) and free table entries are reused
* (an entry is free if its stream field is NULL), but the table is never
* contracted.
*/
typedef struct {
FILE *stream;
int prochnd;
} IDpair;
/* number of entries in idpairs table
*/
#ifndef _UNICODE
unsigned __idtabsiz = 0;
#else /* _UNICODE */
extern unsigned __idtabsiz;
#endif /* _UNICODE */
/* pointer to first table entry
*/
#ifndef _UNICODE
IDpair *__idpairs = NULL;
#else /* _UNICODE */
extern IDpair *__idpairs;
#endif /* _UNICODE */
/* function to find specified table entries. also, creates and maintains
* the table.
*/
static IDpair * __cdecl idtab(FILE *);
/***
*FILE *_popen(cmdstring,type) - initiate a pipe and a child command
*
*Purpose:
* Creates a pipe and asynchronously executes a child copy of the command
* processor with cmdstring (see system()). If the type string contains
* an 'r', the calling process can read child command's standard output
* via the returned stream. If the type string contains a 'w', the calling
* process can write to the child command's standard input via the
* returned stream.
*
*Entry:
* _TSCHAR *cmdstring - command to be executed
* _TSCHAR *type - string of the form "r|w[b|t]", determines the mode
* of the returned stream (i.e., read-only vs write-only,
* binary vs text mode)
*
*Exit:
* If successful, returns a stream associated with one end of the created
* pipe (the other end of the pipe is associated with either the child
* command's standard input or standard output).
*
* If an error occurs, NULL is returned.
*
*Exceptions:
*
*******************************************************************************/
FILE * __cdecl _tpopen (
const _TSCHAR *cmdstring,
const _TSCHAR *type
)
{
int phdls[2]; /* I/O handles for pipe */
int ph_open[2]; /* flags, set if correspond phdls is open */
int i1; /* index into phdls[] */
int i2; /* index into phdls[] */
int tm = 0; /* flag indicating text or binary mode */
int stdhdl; /* either STDIN or STDOUT */
HANDLE osfhndsv1; /* used to save _osfhnd(stdhdl) */
long osfhndsv2; /* used to save _osfhnd(phdls[i2]) */
char osfilesv1; /* used to save _osfile(stdhdl) */
char osfilesv2; /* used to save _osfile(phdls[i2]) */
HANDLE oldhnd; /* used to hold OS file handle values... */
HANDLE newhnd; /* ...in calls to DuplicateHandle API */
FILE *pstream; /* stream to be associated with pipe */
HANDLE prochnd; /* handle for current process */
_TSCHAR *cmdexe; /* pathname for the command processor */
int childhnd; /* handle for child process (cmd.exe) */
IDpair *locidpair; /* pointer to IDpair table entry */
/* first check for errors in the arguments
*/
if ( (cmdstring == NULL) || (type == NULL) || ((*type != 'w') &&
(*type != _T('r'))) )
goto error1;
/* do the _pipe(). note that neither of the resulting handles will
* be inheritable.
*/
if ( *(type + 1) == _T('t') )
tm = _O_TEXT;
else if ( *(type + 1) == _T('b') )
tm = _O_BINARY;
tm |= _O_NOINHERIT;
if ( _pipe( phdls, PSIZE, tm ) == -1 )
goto error1;
/* test *type and set stdhdl, i1 and i2 accordingly.
*/
if ( *type == _T('w') ) {
stdhdl = STDIN;
i1 = 0;
i2 = 1;
}
else {
stdhdl = STDOUT;
i1 = 1;
i2 = 0;
}
/* the pipe now exists. the following steps must be carried out before
* the child process (cmd.exe) may be spawned:
*
* 1. save a non-inheritable dup of stdhdl
*
* 2. force stdhdl to be a dup of ph[i1]. close both ph[i1] and
* the original OS handle underlying stdhdl
*
* 3. associate a stdio-level stream with ph[i2].
*/
/* set flags to indicate pipe handles are open. note, these are only
* used for error recovery.
*/
ph_open[ 0 ] = ph_open[ 1 ] = 1;
/* get the process handle, it will be needed in some API calls
*/
prochnd = GetCurrentProcess();
/* MULTI-THREAD: ASSERT LOCK ON STDHDL HERE!!!!
*/
_lock_fh( stdhdl );
/* save a non-inheritable copy of stdhdl for later restoration.
*/
oldhnd = (HANDLE)_osfhnd( stdhdl );
if ( (oldhnd == INVALID_HANDLE_VALUE) ||
!DuplicateHandle( prochnd,
oldhnd,
prochnd,
&osfhndsv1,
0L,
FALSE, /* non-inheritable */
DUPLICATE_SAME_ACCESS )
) {
goto error2;
}
osfilesv1 = _osfile( stdhdl );
/* force stdhdl to an inheritable dup of phdls[i1] (i.e., force
* STDIN to the pipe read handle or STDOUT to the pipe write handle)
* and close phdls[i1] (so there won't be a stray open handle on the
* pipe after a _pclose). also, clear ph_open[i1] flag so that error
* recovery won't try to close it again.
*/
if ( !DuplicateHandle( prochnd,
(HANDLE)_osfhnd( phdls[i1] ),
prochnd,
&newhnd,
0L,
TRUE, /* inheritable */
DUPLICATE_SAME_ACCESS )
) {
goto error3;
}
(void)CloseHandle( (HANDLE)_osfhnd(stdhdl) );
_free_osfhnd( stdhdl );
_set_osfhnd( stdhdl, (long)newhnd );
_osfile( stdhdl ) = _osfile( phdls[i1] );
(void)_close( phdls[i1] );
ph_open[ i1 ] = 0;
/* associate a stream with phdls[i2]. note that if there are no
* errors, pstream is the return value to the caller.
*/
if ( (pstream = _tfdopen( phdls[i2], type )) == NULL )
goto error4;
/* MULTI-THREAD: ASSERT LOCK ON IDPAIRS HERE!!!!
*/
_mlock( _POPEN_LOCK );
/* next, set locidpair to a free entry in the idpairs table.
*/
if ( (locidpair = idtab( NULL )) == NULL )
goto error5;
/* temporarily change the osfhnd and osfile entries so that
* the child doesn't get any entries for phdls[i2].
*/
osfhndsv2 = _osfhnd( phdls[i2] );
_osfhnd( phdls[i2] ) = (long)INVALID_HANDLE_VALUE;
osfilesv2 = _osfile( phdls[i2] );
_osfile( phdls[i2] ) = 0;
/* spawn the child copy of cmd.exe. the algorithm is adapted from
* SYSTEM.C, and behaves the same way.
*/
if ( ((cmdexe = _tgetenv(_T("COMSPEC"))) == NULL) ||
(((childhnd = _tspawnl( _P_NOWAIT,
cmdexe,
cmdexe,
_T("/c"),
cmdstring,
NULL ))
== -1) && ((errno == ENOENT) || (errno == EACCES))) ) {
/*
* either COMSPEC wasn't defined, or the spawn failed because
* cmdexe wasn't found or was inaccessible. in either case, try to
* spawn "cmd.exe" (Windows NT) or "command.com" (Windows 95) instead
* Note that spawnlp is used here so that the path is searched.
*/
cmdexe = ( _osver & 0x8000 ) ? _T("command.com") : _T("cmd.exe");
childhnd = _tspawnlp( _P_NOWAIT,
cmdexe,
cmdexe,
_T("/c"),
cmdstring,
NULL);
}
_osfhnd( phdls[i2] ) = osfhndsv2;
_osfile( phdls[i2] ) = osfilesv2;
/* check if the last (perhaps only) spawn attempt was successful
*/
if ( childhnd == -1 )
goto error6;
/* restore stdhdl for the current process, set value of *locidpair,
* close osfhndsv1 (note that CloseHandle must be used instead of close)
* and return pstream to the caller
*/
(void)DuplicateHandle( prochnd,
osfhndsv1,
prochnd,
&newhnd,
0L,
TRUE, /* inheritable */
DUPLICATE_CLOSE_SOURCE | /* close osfhndsv1 */
DUPLICATE_SAME_ACCESS );
(void)CloseHandle( (HANDLE)_osfhnd(stdhdl) );
_free_osfhnd( stdhdl );
_set_osfhnd( stdhdl, (long)newhnd );
_osfile(stdhdl) = osfilesv1;
/* MULTI-THREAD: RELEASE LOCK ON STDHDL HERE!!!!
*/
_unlock_fh( stdhdl );
locidpair->prochnd = childhnd;
locidpair->stream = pstream;
/* MULTI-THREAD: RELEASE LOCK ON IDPAIRS HERE!!!!
*/
_munlock( _POPEN_LOCK );
/* all successful calls to _popen return to the caller via this return
* statement!
*/
return( pstream );
/**
* error handling code. all detected errors end up here, entering
* via a goto one of the labels. note that the logic is currently
* a straight fall-thru scheme (e.g., if entered at error5, the
* code for error5, error4,...,error1 is all executed).
**********************************************************************/
error6: /* make sure locidpair is reusable
*/
locidpair->stream = NULL;
error5: /* close pstream (also, clear ph_open[i2] since the stream
* close will also close the pipe handle)
*/
(void)fclose( pstream );
ph_open[ i2 ] = 0;
/* MULTI-THREAD: RELEASE LOCK ON IDPAIRS HERE!!!!
*/
_munlock(_POPEN_LOCK);
error4: /* restore stdhdl
*/
(void)DuplicateHandle( prochnd,
osfhndsv1,
prochnd,
&newhnd,
0L,
TRUE,
DUPLICATE_SAME_ACCESS );
(void)CloseHandle( (HANDLE)_osfhnd(stdhdl) );
_free_osfhnd( stdhdl );
_set_osfhnd( stdhdl, (long)newhnd );
_osfile( stdhdl ) = osfilesv1;
/* MULTI-THREAD: RELEASE LOCK ON STDHDL HERE!!!!
*/
_unlock_fh( stdhdl );
error3: /* close osfhndsv1
*/
CloseHandle( osfhndsv1 );
error2: /* close handles on pipe (if they are still open)
*/
if ( ph_open[i1] )
_close( phdls[i1] );
if ( ph_open[i2] )
_close( phdls[i2] );
error1: /* return NULL to the caller indicating failure
*/
return( NULL );
}
#ifndef _UNICODE
/***
*int _pclose(pstream) - wait on a child command and close the stream on the
* associated pipe
*
*Purpose:
* Closes pstream then waits on the associated child command. The
* argument, pstream, must be the return value from a previous call to
* _popen. _pclose first looks up the process handle of child command
* started by that _popen and does a cwait on it. Then, it closes pstream
* and returns the exit status of the child command to the caller.
*
*Entry:
* FILE *pstream - file stream returned by a previous call to _popen
*
*Exit:
* If successful, _pclose returns the exit status of the child command.
* The format of the return value is that same as for cwait, except that
* the low order and high order bytes are swapped.
*
* If an error occurs, -1 is returned.
*
*Exceptions:
*
*******************************************************************************/
int __cdecl _pclose (
FILE *pstream
)
{
IDpair *locidpair; /* pointer to entry in idpairs table */
int termstat; /* termination status word */
int retval = -1; /* return value (to caller) */
/* MULTI-THREAD: LOCK IDPAIRS HERE!!!!
*/
_mlock(_POPEN_LOCK);
if ( (pstream == NULL) || ((locidpair = idtab(pstream)) == NULL) )
/* invalid pstream, exit with retval == -1
*/
goto done;
/* close pstream
*/
(void)fclose(pstream);
/* wait on the child (copy of the command processor) and all of its
* children.
*/
if ( (_cwait(&termstat, locidpair->prochnd, _WAIT_GRANDCHILD) != -1) ||
(errno == EINTR) )
retval = termstat;
/* Mark the IDpairtable entry as free (note: prochnd was closed by the
* preceding call to _cwait).
*/
locidpair->stream = NULL;
locidpair->prochnd = 0;
/* only return path!
*/
done:
/* MULTI-THREAD: RELEASE LOCK ON IDPAIRS HERE!!!!
*/
_munlock(_POPEN_LOCK);
return(retval);
}
#endif /* _UNICODE */
/***
* static IDpair * idtab(FILE *pstream) - find an idpairs table entry
*
*Purpose:
* Find an entry in the idpairs table. This function finds the entry the
* idpairs table entry corresponding to pstream. In the case where pstream
* is NULL, the entry being searched for is any free entry. In this case,
* idtab will create the idpairs table if it doesn't exist, or expand it (by
* exactly one entry) if there are no free entries.
*
* [MTHREAD NOTE: This routine assumes that the caller has acquired the
* idpairs table lock.]
*
*Entry:
* FILE *pstream - stream corresponding to table entry to be found (if NULL
* then find any free table entry)
*
*Exit:
* if successful, returns a pointer to the idpairs table entry. otherwise,
* returns NULL.
*
*Exceptions:
*
*******************************************************************************/
static IDpair * __cdecl idtab (
FILE *pstream
)
{
IDpair * pairptr; /* ptr to entry */
IDpair * newptr; /* ptr to newly malloc'd memory */
/* search the table. if table is empty, appropriate action should
* fall out automatically.
*/
for ( pairptr = __idpairs ; pairptr < (__idpairs+__idtabsiz) ; pairptr++ )
if ( pairptr->stream == pstream )
break;
/* if we found an entry, return it.
*/
if ( pairptr < (__idpairs + __idtabsiz) )
return(pairptr);
/* did not find an entry in the table. if pstream was NULL, then try
* creating/expanding the table. otherwise, return NULL. note that
* when the table is created or expanded, exactly one new entry is
* produced. this must not be changed unless code is added to mark
* the extra entries as being free (i.e., set their stream fields to
* to NULL).
*/
if ( (pstream != NULL) || ((newptr = (IDpair *)_realloc_crt((void *)__idpairs,
(__idtabsiz + 1)*sizeof(IDpair))) == NULL) )
/* either pstream was non-NULL or the attempt to create/expand
* the table failed. in either case, return a NULL to indicate
* failure.
*/
return( NULL );
__idpairs = newptr; /* new table ptr */
pairptr = newptr + __idtabsiz; /* first new entry */
__idtabsiz++; /* new table size */
return( pairptr );
}