class KProcess

Child process invocation, monitoring and control. More...

Definition#include <kprocess.h>
InheritsQObject (qt)
Inherited byKShellProcess
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Detailed Description

Child process invocation, monitoring and control.

1) General usage and features

This class allows a KDE application to start child processes without having to worry about UN*X signal handling issues and zombie process reaping.

Basically, this class distinguishes three different ways of running child processes:

Starting a DontCare child process means that the application is not interested in any notification to determine whether the child process has already exited or not.

When the child process exits, the KProcess instance corresponding to it emits the Qt signal processExited().

Since this signal is @bf not emitted from within a UN*X signal handler, arbitrary function calls can be made.

KProcess also provides several functions for determining the exit status and the pid of the child process it represents.

Furthermore it is possible to supply command-line arguments to the process in a clean fashion (no null -- terminated stringlists and such...)

A small usage example:


KProcess proc;

proc << "my_executable";
proc << "These" << "are" << "the" << "command" << "line" << "args";
QApplication::connect(&proc, SIGNAL(processExited(KProcess *)), 
                      pointer_to_my_object, SLOT(my_objects_slot));
proc.start();

This will start "my_executable" with the commandline arguments "These"...

When the child process exits, the respective Qt signal will be emitted.

2) Communication with the child process

KProcess supports communication with the child process through stdin/stdout/stderr.

The following functions are provided for getting data from the child process or sending data to the child's stdin (For more information, have a look at the documentation of each function):

QT signals:

enum Communication {NoCommunication = 0, Stdin = 1, Stdout = 2, Stderr = 4, AllOutput = 6, All = 7, NoRead }

Modes in which the communication channel can be opened.

If communication for more than one channel is required, the values have to be or'ed together, for example to get communication with stdout as well as with stdin, you would specify Stdin @p | Stdout

If NoRead is specified in conjunction with Stdout, no data is actually read from Stdout but only the signal childOutput(int fd) is emitted.

enum RunMode {DontCare, NotifyOnExit, Block }

Run-modes for a child process.

 KProcess ()

Constructor

KProcess ()

[virtual]

Destructor:

If the process is running when the destructor for this class is called, the child process is killed with a SIGKILL, but only if the run mode is not of type DontCare. Processes started as DontCare keep running anyway.

bool  setExecutable (const QString& proc)

The use of this function is now deprecated. -- Please use the "operator<<" instead of "setExecutable".

Sets the executable to be started with this KProcess object. Returns false if the process is currently running (in that case the executable remains unchanged.)

KProcessoperator<< (const QString& arg)

Sets the executable and the command line argument list for this process.

For example, doing an "ls -l /usr/local/bin" can be achieved by:


  KProcess p;
  ...
  p << "ls" << "-l" << "/usr/local/bin"

void  clearArguments ()

Clear a command line argument list that has been set by using the "operator<<".

bool  start (RunMode runmode = NotifyOnExit, Communication comm = NoCommunication)

[virtual]

Start the process. For a detailed description of the various run modes and communication semantics, have a look at the general description of the KProcess class.

The following problems could cause KProcess:start() to return false:

Parameters:
commSpecifies which communication links should be established to the child process (stdin/stdout/stderr). By default, no communication takes place and the respective communication signals will never get emitted.

Returns: true on success, false on error (see above for error conditions)

bool  kill (int signo = SIGTERM)

[virtual]

Stop the process (by sending it a signal).

Parameters:
signoThe signal to send. The default is SIGTERM.

Returns: true if the signal was delivered successfully.

bool  isRunning ()

Returns: true if the process is (still) considered to be running

pid_t  getPid ()

Returns the process id of the process.

If it is called after the process has exited, it returns the process id of the last child process that was created by this instance of KProcess.

Calling it before any child process has been started by this KProcess instance causes getPid() to return 0.

void  suspend ()

Suspend processing of data from stdout of the child process.

void  resume ()

Resume processing of data from stdout of the child process.

bool  normalExit ()

Returns: @true if the process has already finished and has exited "voluntarily", ie: it has not been killed by a signal.

int  exitStatus ()

Retrieve the exit status of the process.

Please use KProcess::normalExit() to check whether the process has exited cleanly (i.e., KProcess::normalExit() returns true) before calling this function because if the process did not exit normally, it does not have a valid exit status.

bool  writeStdin (const char *buffer, int buflen)

Transmit data to the child process's stdin.

KProcess::writeStdin may return false in the following cases:

Please note that the data is sent to the client asynchronousely, so when this function returns, the data might not have been processed by the child process.

If all the data has been sent to the client, the signal wroteStdin() will be emitted.

Please note that you must not free "buffer" or call writeStdin() again until either a wroteStdin() signal indicates that the data has been sent or a processHasExited() signal shows that the child process is no longer alive...

bool  closeStdin ()

This causes the stdin file descriptor of the child process to be closed indicating an "EOF" to the child.

Returns: false if no communication to the process's stdin had been specified in the call to start().

bool  closeStdout ()

This causes the stdout file descriptor of the child process to be closed.

Returns: false if no communication to the process's stdout had been specified in the call to start().

bool  closeStderr ()

This causes the stderr file descriptor of the child process to be closed.

Returns: false if no communication to the process's stderr had been specified in the call to start().

const QStrList *  args ()

Lets you see what your arguments are for debugging.

void  processExited (KProcess *proc)

[signal]

Emitted after the process has terminated when the process was run in the NotfiyOnExit (==default option to start()) or the Block mode.

void  receivedStdout (KProcess *proc, char *buffer, int buflen)

[signal]

Emitted, when output from the child process has been received on stdout.

To actually get these signals, the respective communication link (stdout/stderr) has to be turned on in start().

You should copy the information contained in buffer to your private data structures before returning from this slot.

Parameters:
bufferThe data received.
buflenThe number of bytes that are available.

void  receivedStdout (int fd, int &len)

[signal]

Emitted when output from the child process has been received on stdout.

To actually get these signals, the respective communications link (stdout/stderr) has to be turned on in start() and the NoRead flag should have been passed.

The data still has to be read from file descriptor fd.

void  receivedStderr (KProcess *proc, char *buffer, int buflen)

[signal]

Emitted, when output from the child process has been received on stderr. To actually get these signals, the respective communication link (stdout/stderr) has to be turned on in start().

You should copy the information contained in buffer to your private data structures before returning from this slot.

Parameters:
bufferThe data received.
buflenThe number of bytes that are available.

void  wroteStdin (KProcess *proc)

[signal]

Emitted after all the data that has been specified by a prior call to writeStdin() has actually been written to the child process.

void  slotChildOutput (int fdno)

[protected slot]

This slot gets activated when data from the child's stdout arrives. It usually calls "childOutput"

void  slotChildError (int fdno)

[protected slot]

This slot gets activated when data from the child's stderr arrives. It usually calls "childError"

void  slotSendData (int dummy)

[protected slot]

Called when another bulk of data can be sent to the child's stdin. If there is no more data to be sent to stdin currently available, this function must disable the QSocketNotifier "innot".

QStrList arguments

[protected]

The list of the process' command line arguments. The first entry in this list is the executable itself.

RunMode run_mode

[protected]

How to run the process (Block, NotifyOnExit, DontCare). You should not modify this data member directly from derived classes.

bool runs

[protected]

true if the process is currently running. You should not modify this data member directly from derived classes. For reading the value of this data member, please use "isRunning()" since "runs" will probably be made private in later versions of KProcess.

pid_t pid

[protected]

The PID of the currently running process (see "getPid()"). You should not modify this data member in derived classes. Please use "getPid()" instead of directly accessing this member function since it will probably be made private in later versions of KProcess.

int status

[protected]

The process' exit status as returned by "waitpid". You should not modify the value of this data member from derived classes. You should rather use "getStatus()" than accessing this data member directly since it will probably be made private in further versions of KProcess.

int  setupCommunication (Communication comm)

[protected virtual]

This function is called from "KProcess::start" right before a "fork" takes place. According to the "comm" parameter this function has to initialize the "in", "out" and "err" data member of KProcess.

This function should return 0 if setting the needed communication channels was successful.

The default implementation is to create UNIX STREAM sockets for the communication, but you could overload this function and establish a TCP/IP communication for network communication, for example.

int  commSetupDoneP ()

[protected virtual]

Called right after a (successful) fork on the parent side. This function will usually do some communications cleanup, like closing the reading end of the "stdin" communication channel.

Furthermore, it must also create the QSocketNotifiers "innot", "outnot" and "errnot" and connect their Qt slots to the respective KProcess member functions.

For a more detailed explanation, it is best to have a look at the default implementation of "setupCommunication" in kprocess.cpp.

int  commSetupDoneC ()

[protected virtual]

Called right after a (successful) fork, but before an "exec" on the child process' side. It usually just closes the unused communication ends of "in", "out" and "err" (like the writing end of the "in" communication channel.

void  processHasExited (int state)

[protected virtual]

Immediately called after a process has exited. This function normally calls commClose to close all open communication channels to this process and emits the "processExited" signal (if the process was not running in the "DontCare" mode).

void  commClose ()

[protected virtual]

Should clean up the communication links to the child after it has exited. Should be called from "processHasExited".

int [2] out

[protected]

the socket descriptors for stdin/stdout/stderr.

QSocketNotifier * innot

[protected]

The socket notifiers for the above socket descriptors.

Communication communication

[protected]

Lists the communication links that are activated for the child process. Should not be modified from derived classes.

int  childOutput (int fdno)

[protected]

Called by "slotChildOutput" this function copies data arriving from the child process's stdout to the respective buffer and emits the signal "receivedStderr".

int  childError (int fdno)

[protected]

Called by "slotChildOutput" this function copies data arriving from the child process's stdout to the respective buffer and emits the signal "receivedStderr"

friend class KProcessController

[protected]

KProcessController is a friend of KProcess because it has to have access to various data members.