Class: Gio::Subprocess

Inherits:
Object
  • Object
show all
Defined in:
(unknown)

Overview

#GSubprocess allows the creation of and interaction with child processes.

Processes can be communicated with using standard GIO-style APIs (ie: GInput::Stream, #GOutputStream). There are GIO-style APIs to wait for process termination (ie: cancellable and with an asynchronous variant).

There is an API to force a process to terminate, as well as a race-free API for sending UNIX signals to a subprocess.

One major advantage that GIO brings over the core GLib library is comprehensive API for asynchronous I/O, such g_output_stream_splice_async(). This makes GSubprocess significantly more powerful and flexible than equivalent APIs in some other languages such as the ‘subprocess.py` included with Python. For example, using #GSubprocess one could create two child processes, reading standard output from the first, processing it, and writing to the input stream of the second, all without blocking the main loop.

A powerful g_subprocess_communicate() API is provided similar to the ‘communicate()` method of `subprocess.py`. This enables very easy interaction with a subprocess that has been opened with pipes.

#GSubprocess defaults to tight control over the file descriptors open in the child process, avoiding dangling-fd issues that are caused by a simple fork()/exec(). The only open file descriptors in the spawned process are ones that were explicitly specified by the #GSubprocess API (unless %G_SUBPROCESS_FLAGS_INHERIT_FDS was specified).

#GSubprocess will quickly reap all child processes as they exit, avoiding “zombie processes” remaining around for long periods of time. g_subprocess_wait() can be used to wait for this to happen, but it will happen even without the call being explicitly made.

As a matter of principle, #GSubprocess has no API that accepts shell-style space-separated strings. It will, however, match the typical shell behaviour of searching the PATH for executables that do not contain a directory separator in their name.

#GSubprocess attempts to have a very simple API for most uses (ie: spawning a subprocess with arguments and support for most typical kinds of input and output redirection). See g_subprocess_new(). The GSubprocess::Launcher API is provided for more complicated cases (advanced types of redirection, environment variable manipulation, change of working directory, child setup functions, etc).

A typical use of #GSubprocess will involve calling g_subprocess_new(), followed by g_subprocess_wait_async() or g_subprocess_wait(). After the process exits, the status can be checked using functions such as g_subprocess_get_if_exited() (which are similar to the familiar WIFEXITED-style POSIX macros).

Instance Method Summary collapse

Instance Method Details

#argv=(argv) ⇒ Gio::

Returns argv.

Parameters:

Returns:

#communicate(stdin_buf, cancellable, stdout_buf, stderr_buf) ⇒ TrueClass

Communicate with the subprocess until it terminates, and all input and output has been completed.

If stdin_buf is given, the subprocess must have been created with %G_SUBPROCESS_FLAGS_STDIN_PIPE. The given data is fed to the stdin of the subprocess and the pipe is closed (ie: EOF).

At the same time (as not to cause blocking when dealing with large amounts of data), if %G_SUBPROCESS_FLAGS_STDOUT_PIPE or %G_SUBPROCESS_FLAGS_STDERR_PIPE were used, reads from those streams. The data that was read is returned in stdout and/or the stderr.

If the subprocess was created with %G_SUBPROCESS_FLAGS_STDOUT_PIPE, stdout_buf will contain the data read from stdout. Otherwise, for subprocesses not created with %G_SUBPROCESS_FLAGS_STDOUT_PIPE, stdout_buf will be set to nil. Similar provisions apply to stderr_buf and %G_SUBPROCESS_FLAGS_STDERR_PIPE.

As usual, any output variable may be given as nil to ignore it.

If you desire the stdout and stderr data to be interleaved, create the subprocess with %G_SUBPROCESS_FLAGS_STDOUT_PIPE and %G_SUBPROCESS_FLAGS_STDERR_MERGE. The merged result will be returned in stdout_buf and stderr_buf will be set to nil.

In case of any error (including cancellation), false will be returned with error set. Some or all of the stdin data may have been written. Any stdout or stderr data that has been read will be discarded. None of the out variables (aside from error) will have been set to anything in particular and should not be inspected.

In the case that true is returned, the subprocess has exited and the exit status inspection APIs (eg: g_subprocess_get_if_exited(), g_subprocess_get_exit_status()) may be used.

You should not attempt to use any of the subprocess pipes after starting this function, since they may be left in strange states, even if the operation was cancelled. You should especially not attempt to interact with the pipes while the operation is in progress (either from another thread or if using the asynchronous version).

Parameters:

  • stdin_buf (GLib::Bytes) —

    data to send to the stdin of the subprocess, or nil

  • cancellable (Gio::Cancellable) —

    a #GCancellable

  • stdout_buf (GLib::Bytes) —

    data read from the subprocess stdout

  • stderr_buf (GLib::Bytes) —

    data read from the subprocess stderr

Returns:

  • (TrueClass) —

    true if successful

#communicate_async(stdin_buf, cancellable, callback, user_data) ⇒ nil

Asynchronous version of g_subprocess_communicate(). Complete invocation with g_subprocess_communicate_finish().

Parameters:

  • stdin_buf (GLib::Bytes) —

    Input data, or nil

  • cancellable (Gio::Cancellable) —

    Cancellable

  • callback (Gio::AsyncReadyCallback) —

    Callback

  • user_data (GObject) —

    User data

Returns:

  • (nil)

#communicate_finish(result, stdout_buf, stderr_buf) ⇒ TrueClass

Complete an invocation of g_subprocess_communicate_async().

Parameters:

  • result (Gio::AsyncResult) —

    Result

  • stdout_buf (GLib::Bytes) —

    Return location for stdout data

  • stderr_buf (GLib::Bytes) —

    Return location for stderr data

Returns:

  • (TrueClass)

#communicate_utf8(stdin_buf, cancellable, stdout_buf, stderr_buf) ⇒ TrueClass

Like g_subprocess_communicate(), but validates the output of the process as UTF-8, and returns it as a regular NUL terminated string.

On error, stdout_buf and stderr_buf will be set to undefined values and should not be used.

Parameters:

  • stdin_buf (String) —

    data to send to the stdin of the subprocess, or nil

  • cancellable (Gio::Cancellable) —

    a #GCancellable

  • stdout_buf (String) —

    data read from the subprocess stdout

  • stderr_buf (String) —

    data read from the subprocess stderr

Returns:

  • (TrueClass)

#communicate_utf8_async(stdin_buf, cancellable, callback, user_data) ⇒ nil

Asynchronous version of g_subprocess_communicate_utf8(). Complete invocation with g_subprocess_communicate_utf8_finish().

Parameters:

  • stdin_buf (String) —

    Input data, or nil

  • cancellable (Gio::Cancellable) —

    Cancellable

  • callback (Gio::AsyncReadyCallback) —

    Callback

  • user_data (GObject) —

    User data

Returns:

  • (nil)

#communicate_utf8_finish(result, stdout_buf, stderr_buf) ⇒ TrueClass

Complete an invocation of g_subprocess_communicate_utf8_async().

Parameters:

  • result (Gio::AsyncResult) —

    Result

  • stdout_buf (String) —

    Return location for stdout data

  • stderr_buf (String) —

    Return location for stderr data

Returns:

  • (TrueClass)

#exit_status ⇒ Integer

Check the exit status of the subprocess, given that it exited normally. This is the value passed to the exit() system call or the return value from main.

This is equivalent to the system WEXITSTATUS macro.

It is an error to call this function before g_subprocess_wait() and unless g_subprocess_get_if_exited() returned true.

Returns:

  • (Integer) —

    the exit status

#flags=(flags) ⇒ Gio::SubprocessFlags

Returns flags.

Parameters:

Returns:

#force_exit ⇒ nil

Use an operating-system specific method to attempt an immediate, forceful termination of the process. There is no mechanism to determine whether or not the request itself was successful; however, you can use g_subprocess_wait() to monitor the status of the process after calling this function.

On Unix, this function sends %SIGKILL.

Returns:

  • (nil)

#identifier ⇒ String

On UNIX, returns the process ID as a decimal string. On Windows, returns the result of GetProcessId() also as a string. If the subprocess has terminated, this will return nil.

Returns:

  • (String) —

    the subprocess identifier, or nil if the subprocess has terminated

#if_exited ⇒ TrueClass

Check if the given subprocess exited normally (ie: by way of exit() or return from main()).

This is equivalent to the system WIFEXITED macro.

It is an error to call this function before g_subprocess_wait() has returned.

Returns:

  • (TrueClass) —

    true if the case of a normal exit

#if_signaled ⇒ TrueClass

Check if the given subprocess terminated in response to a signal.

This is equivalent to the system WIFSIGNALED macro.

It is an error to call this function before g_subprocess_wait() has returned.

Returns:

  • (TrueClass) —

    true if the case of termination due to a signal

#new(flags, error, argv0, array) ⇒ Gio::Subprocess

Create a new process with the given flags and varargs argument list. By default, matching the g_spawn_async() defaults, the child’s stdin will be set to the system null device, and stdout/stderr will be inherited from the parent. You can use flags to control this behavior.

The argument list must be terminated with nil.

Parameters:

  • flags (Gio::SubprocessFlags) —

    flags that define the behaviour of the subprocess

  • error (GLib::Error) —

    return location for an error, or nil

  • argv0 (String) —

    first commandline argument to pass to the subprocess

  • array (Array) —

    more commandline arguments, followed by nil

Returns:

  • (Gio::Subprocess) —

    A newly created #GSubprocess, or nil on error (and error will be set)

#newv(argv, flags) ⇒ Gio::Subprocess

Create a new process with the given flags and argument list.

The argument list is expected to be nil-terminated.

Parameters:

  • argv (Array<Gio::filename>) —

    commandline arguments for the subprocess

  • flags (Gio::SubprocessFlags) —

    flags that define the behaviour of the subprocess

Returns:

  • (Gio::Subprocess) —

    A newly created #GSubprocess, or nil on error (and error will be set)

#send_signal(signal_num) ⇒ nil

Sends the UNIX signal signal_num to the subprocess, if it is still running.

This API is race-free. If the subprocess has terminated, it will not be signalled.

This API is not available on Windows.

Parameters:

  • signal_num (Integer) —

    the signal number to send

Returns:

  • (nil)

#status ⇒ Integer

Gets the raw status code of the process, as from waitpid().

This value has no particular meaning, but it can be used with the macros defined by the system headers such as WIFEXITED. It can also be used with g_spawn_check_exit_status().

It is more likely that you want to use g_subprocess_get_if_exited() followed by g_subprocess_get_exit_status().

It is an error to call this function before g_subprocess_wait() has returned.

Returns:

  • (Integer) —

    the (meaningless) waitpid() exit status from the kernel

#stderr_pipe ⇒ Gio::InputStream

Gets the GInput::Stream from which to read the stderr output of subprocess.

The process must have been created with %G_SUBPROCESS_FLAGS_STDERR_PIPE.

Returns:

#stdin_pipe ⇒ Gio::OutputStream

Gets the GOutput::Stream that you can write to in order to give data to the stdin of subprocess.

The process must have been created with %G_SUBPROCESS_FLAGS_STDIN_PIPE.

Returns:

#stdout_pipe ⇒ Gio::InputStream

Gets the GInput::Stream from which to read the stdout output of subprocess.

The process must have been created with %G_SUBPROCESS_FLAGS_STDOUT_PIPE.

Returns:

#successful ⇒ TrueClass

Checks if the process was “successful”. A process is considered successful if it exited cleanly with an exit status of 0, either by way of the exit() system call or return from main().

It is an error to call this function before g_subprocess_wait() has returned.

Returns:

  • (TrueClass) —

    true if the process exited cleanly with a exit status of 0

#term_sig ⇒ Integer

Get the signal number that caused the subprocess to terminate, given that it terminated due to a signal.

This is equivalent to the system WTERMSIG macro.

It is an error to call this function before g_subprocess_wait() and unless g_subprocess_get_if_signaled() returned true.

Returns:

  • (Integer) —

    the signal causing termination

#wait(cancellable) ⇒ TrueClass

Synchronously wait for the subprocess to terminate.

After the process terminates you can query its exit status with functions such as g_subprocess_get_if_exited() and g_subprocess_get_exit_status().

This function does not fail in the case of the subprocess having abnormal termination. See g_subprocess_wait_check() for that.

Cancelling cancellable doesn’t kill the subprocess. Call g_subprocess_force_exit() if it is desirable.

Parameters:

Returns:

  • (TrueClass) —

    true on success, false if cancellable was cancelled

#wait_async(cancellable, callback, user_data) ⇒ nil

Wait for the subprocess to terminate.

This is the asynchronous version of g_subprocess_wait().

Parameters:

  • cancellable (Gio::Cancellable) —

    a #GCancellable, or nil

  • callback (Gio::AsyncReadyCallback) —

    a GAsync::ReadyCallback to call when the operation is complete

  • user_data (GObject) —

    user_data for callback

Returns:

  • (nil)

#wait_check(cancellable) ⇒ TrueClass

Combines g_subprocess_wait() with g_spawn_check_exit_status(). cancellable was cancelled

Parameters:

Returns:

  • (TrueClass) —

    true on success, false if process exited abnormally, or

#wait_check_async(cancellable, callback, user_data) ⇒ nil

Combines g_subprocess_wait_async() with g_spawn_check_exit_status().

This is the asynchronous version of g_subprocess_wait_check().

Parameters:

  • cancellable (Gio::Cancellable) —

    a #GCancellable, or nil

  • callback (Gio::AsyncReadyCallback) —

    a GAsync::ReadyCallback to call when the operation is complete

  • user_data (GObject) —

    user_data for callback

Returns:

  • (nil)

#wait_check_finish(result) ⇒ TrueClass

Collects the result of a previous call to g_subprocess_wait_check_async().

Parameters:

  • result (Gio::AsyncResult) —

    the GAsync::Result passed to your #GAsyncReadyCallback

Returns:

  • (TrueClass) —

    true if successful, or false with error set

#wait_finish(result) ⇒ TrueClass

Collects the result of a previous call to g_subprocess_wait_async().

Parameters:

  • result (Gio::AsyncResult) —

    the GAsync::Result passed to your #GAsyncReadyCallback

Returns:

  • (TrueClass) —

    true if successful, or false with error set