The following listing contains the interface of the Pipes unit.
This unit provides routines to start a child process and write to/read from its Input/Output/StdErr via pipes. All of this is emulated transparently under Dos as far as possible.
{ Piping data from and to processes Copyright (C) 1998-2005 Free Software Foundation, Inc. Author: Frank Heckenbach <frank@pascal.gnu.de> This file is part of GNU Pascal. GNU Pascal is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Pascal is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Pascal; see the file COPYING. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. As a special exception, if you link this file with files compiled with a GNU compiler to produce an executable, this does not cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. } {$gnu-pascal,I-} {$if __GPC_RELEASE__ < 20030303} {$error This unit requires GPC release 20030303 or newer.} {$endif} { Keep this consistent with the one in pipesc.c } {$if defined (MSDOS) or defined (__MINGW32__)} {$define NOFORK} {$endif} unit Pipes; interface uses GPC; const PipeForking = {$ifdef NOFORK} False {$else} True {$endif}; type TProcedure = procedure; PWaitPIDResult = ^TWaitPIDResult; TWaitPIDResult = (PIDNothing, PIDExited, PIDSignaled, PIDStopped, PIDUnknown); PPipeProcess = ^TPipeProcess; TPipeProcess = record PID : Integer; { Process ID of process forked } SignalPID: Integer; { Process ID to send the signal to. Equals PID by default } OpenPipes: Integer; { Number of pipes to/from the process, for internal use } Signal : Integer; { Send this signal (if not 0) to the process after all pipes have been closed after some time } Seconds : Integer; { Wait so many seconds before sending the signal if the process has not terminated by itself } Wait : Boolean; { Wait for the process, even longer than Seconds seconds, after sending the signal (if any) } Result : PWaitPIDResult; { Default nil. If a pointer to a variable is stored here, its destination will contain the information whether the process terminated by itself, or was terminated or stopped by a signal, when waiting after closing the pipes } Status : ^Integer; { Default nil. If a pointer to a variable is stored here, its destination will contain the exit status if the process terminated by itself, or the number of the signal otherwise, when waiting after closing the pipes } end; var { Default values for TPipeProcess records created by Pipe } DefaultPipeSignal : Integer = 0; DefaultPipeSeconds: Integer = 0; DefaultPipeWait : Boolean = True; { The procedure Pipe starts a process whose name is given by ProcessName, with the given parameters (can be Null if no parameters) and environment, and create pipes from and/or to the process' standard input/output/error. ProcessName is searched for in the PATH with FSearchExecutable. Any of ToInputFile, FromOutputFile and FromStdErrFile can be Null if the corresponding pipe is not wanted. FromOutputFile and FromStdErrFile may be identical, in which case standard output and standard error are redirected to the same pipe. The behaviour of other pairs of files being identical is undefined, and useless, anyway. The files are Assigned and Reset or Rewritten as appropriate. Errors are returned in IOResult. If Process is not Null, a pointer to a record is stored there, from which the PID of the process created can be read, and by writing to which the action after all pipes have been closed can be changed. (The record is automatically Dispose'd of after all pipes have been closed.) If automatic waiting is turned off, the caller should get the PID from the record before it's Dispose'd of, and wait for the process sometime in order to avoid zombies. If no redirections are performed (i.e., all 3 files are Null), the caller should wait for the process with WaitPipeProcess. When an error occurs, Process is not assigned to, and the state of the files is undefined, so be sure to check IOResult before going on. ChildProc, if not nil, is called in the child process after forking and redirecting I/O, but before executing the new process. It can even be called instead of executing a new process (ProcessName can be empty then). The procedure even works under Dos, but, of course, in a limited sense: if ToInputFile is used, the process will not actually be started until ToInputFile is closed. Signal, Seconds and Wait of TPipeProcess are ignored, and PID and SignalPID do not contain a Process ID, but an internal value without any meaning to the caller. Result will always be PIDExited. So, Status is the only interesting field (but Result should also be checked). Since there is no forking under Dos, ChildProc, if not nil, is called in the main process before spawning the program. So, to be portable, it should not do any things that would influence the process after the return of the Pipe function. The only portable way to use "pipes" in both directions is to call Pipe, write all the Input data to ToInputFile, close ToInputFile, and then read the Output and StdErr data from FromOutputFile and FromStdErrFile. However, since the capacity of pipes is limited, one should also check for Data from FromOutputFile and FromStdErrFile (using CanRead, IOSelect or IOSelectRead) while writing the Input data (under Dos, there simply won't be any data then, but checking for data doesn't do any harm). Please see pipedemo.pas for an example. } procedure Pipe (var ToInputFile, FromOutputFile, FromStdErrFile: AnyFile; const ProcessName: String; protected var Parameters: TPStrings; ProcessEnvironment: PCStrings; var Process: PPipeProcess; ChildProc: TProcedure); attribute (iocritical); { Waits for a process created by Pipe as determined in the Process record. (Process is Dispose'd of afterwards.) Returns True if successful. } function WaitPipeProcess (Process: PPipeProcess): Boolean; attribute (ignorable); { Alternative interface from PExecute } const PExecute_First = 1; PExecute_Last = 2; PExecute_One = PExecute_First or PExecute_Last; PExecute_Search = 4; PExecute_Verbose = 8; { PExecute: execute a chain of processes. Program and Arguments are the arguments to execv/execvp. Flags and PExecute_Search is non-zero if $PATH should be searched. Flags and PExecute_First is nonzero for the first process in chain. Flags and PExecute_Last is nonzero for the last process in chain. The result is the pid on systems like Unix where we fork/exec and on systems like MS-Windows and OS2 where we use spawn. It is up to the caller to wait for the child. The result is the exit code on systems like MSDOS where we spawn and wait for the child here. Upon failure, ErrMsg is set to the text of the error message, and -1 is returned. errno is available to the caller to use. PWait: cover function for wait. PID is the process id of the task to wait for. Status is the status argument to wait. Flags is currently unused (allows future enhancement without breaking upward compatibility). Pass 0 for now. The result is the process ID of the child reaped, or -1 for failure. On systems that don't support waiting for a particular child, PID is ignored. On systems like MSDOS that don't really multitask PWait is just a mechanism to provide a consistent interface for the caller. } function PExecute (ProgramName: CString; Arguments: PCStrings; var ErrMsg: String; Flags: Integer): Integer; attribute (ignorable); function PWait (PID: Integer; var Status: Integer; Flags: Integer): Integer; attribute (ignorable);