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GSubprocess

GSubprocess — Child processes

Properties

GStrv argv Write / Construct Only
GSubprocessFlags flags Write / Construct Only

Types and Values

Object Hierarchy

    GObject
    ╰── GSubprocess

Implemented Interfaces

GSubprocess implements GInitable.

Includes

#include <gio/gio.h>

Description

GSubprocess allows the creation of and interaction with child processes.

Processes can be communicated with using standard GIO-style APIs (ie: GInputStream, 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 GSubprocessLauncher 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).

Functions

g_subprocess_new ()

GSubprocess *
g_subprocess_new (GSubprocessFlags flags,
                  GError **error,
                  const gchar *argv0,
                  ...);

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 NULL.

[skip]

Parameters

flags

flags that define the behaviour of the subprocess

 

error

return location for an error, or NULL.

[nullable]

argv0

first commandline argument to pass to the subprocess

 

...

more commandline arguments, followed by NULL

 

Returns

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

Since: 2.40


g_subprocess_newv ()

GSubprocess *
g_subprocess_newv (const gchar * const *argv,
                   GSubprocessFlags flags,
                   GError **error);

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

The argument list is expected to be NULL-terminated.

[rename-to g_subprocess_new]

Parameters

argv

commandline arguments for the subprocess.

[array zero-terminated=1][element-type utf8]

flags

flags that define the behaviour of the subprocess

 

error

return location for an error, or NULL.

[nullable]

Returns

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

Since: 2.40


g_subprocess_get_identifier ()

const gchar *
g_subprocess_get_identifier (GSubprocess *subprocess);

On UNIX, returns the process ID as a decimal string. On Windows, returns the result of GetProcessId() also as a string.

Parameters

subprocess

a GSubprocess

 

g_subprocess_get_stdin_pipe ()

GOutputStream *
g_subprocess_get_stdin_pipe (GSubprocess *subprocess);

Gets the GOutputStream 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.

Parameters

subprocess

a GSubprocess

 

Returns

the stdout pipe.

[transfer none]

Since: 2.40


g_subprocess_get_stdout_pipe ()

GInputStream *
g_subprocess_get_stdout_pipe (GSubprocess *subprocess);

Gets the GInputStream from which to read the stdout output of subprocess .

The process must have been created with G_SUBPROCESS_FLAGS_STDOUT_PIPE.

Parameters

subprocess

a GSubprocess

 

Returns

the stdout pipe.

[transfer none]

Since: 2.40


g_subprocess_get_stderr_pipe ()

GInputStream *
g_subprocess_get_stderr_pipe (GSubprocess *subprocess);

Gets the GInputStream from which to read the stderr output of subprocess .

The process must have been created with G_SUBPROCESS_FLAGS_STDERR_PIPE.

Parameters

subprocess

a GSubprocess

 

Returns

the stderr pipe.

[transfer none]

Since: 2.40


g_subprocess_wait ()

gboolean
g_subprocess_wait (GSubprocess *subprocess,
                   GCancellable *cancellable,
                   GError **error);

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

subprocess

a GSubprocess

 

cancellable

a GCancellable

 

error

a GError

 

Returns

TRUE on success, FALSE if cancellable was cancelled

Since: 2.40


g_subprocess_wait_async ()

void
g_subprocess_wait_async (GSubprocess *subprocess,
                         GCancellable *cancellable,
                         GAsyncReadyCallback callback,
                         gpointer user_data);

Wait for the subprocess to terminate.

This is the asynchronous version of g_subprocess_wait().

Parameters

subprocess

a GSubprocess

 

cancellable

a GCancellable, or NULL

 

callback

a GAsyncReadyCallback to call when the operation is complete

 

user_data

user_data for callback

 

Since: 2.40


g_subprocess_wait_finish ()

gboolean
g_subprocess_wait_finish (GSubprocess *subprocess,
                          GAsyncResult *result,
                          GError **error);

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

Parameters

subprocess

a GSubprocess

 

result

the GAsyncResult passed to your GAsyncReadyCallback

 

error

a pointer to a NULL GError, or NULL

 

Returns

TRUE if successful, or FALSE with error set

Since: 2.40


g_subprocess_wait_check ()

gboolean
g_subprocess_wait_check (GSubprocess *subprocess,
                         GCancellable *cancellable,
                         GError **error);

Combines g_subprocess_wait() with g_spawn_check_exit_status().

Parameters

subprocess

a GSubprocess

 

cancellable

a GCancellable

 

error

a GError

 

Returns

TRUE on success, FALSE if process exited abnormally, or cancellable was cancelled

Since: 2.40


g_subprocess_wait_check_async ()

void
g_subprocess_wait_check_async (GSubprocess *subprocess,
                               GCancellable *cancellable,
                               GAsyncReadyCallback callback,
                               gpointer user_data);

Combines g_subprocess_wait_async() with g_spawn_check_exit_status().

This is the asynchronous version of g_subprocess_wait_check().

Parameters

subprocess

a GSubprocess

 

cancellable

a GCancellable, or NULL

 

callback

a GAsyncReadyCallback to call when the operation is complete

 

user_data

user_data for callback

 

Since: 2.40


g_subprocess_wait_check_finish ()

gboolean
g_subprocess_wait_check_finish (GSubprocess *subprocess,
                                GAsyncResult *result,
                                GError **error);

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

Parameters

subprocess

a GSubprocess

 

result

the GAsyncResult passed to your GAsyncReadyCallback

 

error

a pointer to a NULL GError, or NULL

 

Returns

TRUE if successful, or FALSE with error set

Since: 2.40


g_subprocess_get_successful ()

gboolean
g_subprocess_get_successful (GSubprocess *subprocess);

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.

Parameters

subprocess

a GSubprocess

 

Returns

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

Since: 2.40


g_subprocess_get_if_exited ()

gboolean
g_subprocess_get_if_exited (GSubprocess *subprocess);

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.

Parameters

subprocess

a GSubprocess

 

Returns

TRUE if the case of a normal exit

Since: 2.40


g_subprocess_get_exit_status ()

gint
g_subprocess_get_exit_status (GSubprocess *subprocess);

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.

Parameters

subprocess

a GSubprocess

 

Returns

the exit status

Since: 2.40


g_subprocess_get_if_signaled ()

gboolean
g_subprocess_get_if_signaled (GSubprocess *subprocess);

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.

Parameters

subprocess

a GSubprocess

 

Returns

TRUE if the case of termination due to a signal

Since: 2.40


g_subprocess_get_term_sig ()

gint
g_subprocess_get_term_sig (GSubprocess *subprocess);

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.

Parameters

subprocess

a GSubprocess

 

Returns

the signal causing termination

Since: 2.40


g_subprocess_get_status ()

gint
g_subprocess_get_status (GSubprocess *subprocess);

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.

Parameters

subprocess

a GSubprocess

 

Returns

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

Since: 2.40


g_subprocess_send_signal ()

void
g_subprocess_send_signal (GSubprocess *subprocess,
                          gint signal_num);

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

subprocess

a GSubprocess

 

signal_num

the signal number to send

 

Since: 2.40


g_subprocess_force_exit ()

void
g_subprocess_force_exit (GSubprocess *subprocess);

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.

Parameters

subprocess

a GSubprocess

 

Since: 2.40


g_subprocess_communicate ()

gboolean
g_subprocess_communicate (GSubprocess *subprocess,
                          GBytes *stdin_buf,
                          GCancellable *cancellable,
                          GBytes **stdout_buf,
                          GBytes **stderr_buf,
                          GError **error);

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 NULL. Similar provisions apply to stderr_buf and G_SUBPROCESS_FLAGS_STDERR_PIPE.

As usual, any output variable may be given as NULL 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 NULL.

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

subprocess

a GSubprocess

 

stdin_buf

data to send to the stdin of the subprocess, or NULL.

[nullable]

cancellable

a GCancellable

 

stdout_buf

data read from the subprocess stdout.

[out]

stderr_buf

data read from the subprocess stderr.

[out]

error

a pointer to a NULL GError pointer, or NULL

 

Returns

TRUE if successful

Since: 2.40


g_subprocess_communicate_async ()

void
g_subprocess_communicate_async (GSubprocess *subprocess,
                                GBytes *stdin_buf,
                                GCancellable *cancellable,
                                GAsyncReadyCallback callback,
                                gpointer user_data);

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

Parameters

subprocess

Self

 

stdin_buf

Input data, or NULL.

[nullable]

cancellable

Cancellable.

[nullable]

callback

Callback

 

user_data

User data

 

g_subprocess_communicate_finish ()

gboolean
g_subprocess_communicate_finish (GSubprocess *subprocess,
                                 GAsyncResult *result,
                                 GBytes **stdout_buf,
                                 GBytes **stderr_buf,
                                 GError **error);

Complete an invocation of g_subprocess_communicate_async().

Parameters

subprocess

Self

 

result

Result

 

stdout_buf

Return location for stdout data.

[out]

stderr_buf

Return location for stderr data.

[out]

error

Error

 

g_subprocess_communicate_utf8 ()

gboolean
g_subprocess_communicate_utf8 (GSubprocess *subprocess,
                               const char *stdin_buf,
                               GCancellable *cancellable,
                               char **stdout_buf,
                               char **stderr_buf,
                               GError **error);

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

Parameters

subprocess

a GSubprocess

 

stdin_buf

data to send to the stdin of the subprocess, or NULL.

[nullable]

cancellable

a GCancellable

 

stdout_buf

data read from the subprocess stdout.

[out]

stderr_buf

data read from the subprocess stderr.

[out]

error

a pointer to a NULL GError pointer, or NULL

 

g_subprocess_communicate_utf8_async ()

void
g_subprocess_communicate_utf8_async (GSubprocess *subprocess,
                                     const char *stdin_buf,
                                     GCancellable *cancellable,
                                     GAsyncReadyCallback callback,
                                     gpointer user_data);

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

Parameters

subprocess

Self

 

stdin_buf

Input data, or NULL.

[nullable]

cancellable

Cancellable

 

callback

Callback

 

user_data

User data

 

g_subprocess_communicate_utf8_finish ()

gboolean
g_subprocess_communicate_utf8_finish (GSubprocess *subprocess,
                                      GAsyncResult *result,
                                      char **stdout_buf,
                                      char **stderr_buf,
                                      GError **error);

Complete an invocation of g_subprocess_communicate_utf8_async().

Parameters

subprocess

Self

 

result

Result

 

stdout_buf

Return location for stdout data.

[out]

stderr_buf

Return location for stderr data.

[out]

error

Error

 

Types and Values

GSubprocess

typedef struct _GSubprocess GSubprocess;

A child process.

Since: 2.40


enum GSubprocessFlags

Flags to define the behaviour of a GSubprocess.

Note that the default for stdin is to redirect from /dev/null. For stdout and stderr the default are for them to inherit the corresponding descriptor from the calling process.

Note that it is a programmer error to mix 'incompatible' flags. For example, you may not request both G_SUBPROCESS_FLAGS_STDOUT_PIPE and G_SUBPROCESS_FLAGS_STDOUT_SILENCE.

Members

G_SUBPROCESS_FLAGS_NONE

No flags.

 

G_SUBPROCESS_FLAGS_STDIN_PIPE

create a pipe for the stdin of the spawned process that can be accessed with g_subprocess_get_stdin_pipe().

 

G_SUBPROCESS_FLAGS_STDIN_INHERIT

stdin is inherited from the calling process.

 

G_SUBPROCESS_FLAGS_STDOUT_PIPE

create a pipe for the stdout of the spawned process that can be accessed with g_subprocess_get_stdout_pipe().

 

G_SUBPROCESS_FLAGS_STDOUT_SILENCE

silence the stdout of the spawned process (ie: redirect to /dev/null).

 

G_SUBPROCESS_FLAGS_STDERR_PIPE

create a pipe for the stderr of the spawned process that can be accessed with g_subprocess_get_stderr_pipe().

 

G_SUBPROCESS_FLAGS_STDERR_SILENCE

silence the stderr of the spawned process (ie: redirect to /dev/null).

 

G_SUBPROCESS_FLAGS_STDERR_MERGE

merge the stderr of the spawned process with whatever the stdout happens to be. This is a good way of directing both streams to a common log file, for example.

 

G_SUBPROCESS_FLAGS_INHERIT_FDS

spawned processes will inherit the file descriptors of their parent, unless those descriptors have been explicitly marked as close-on-exec. This flag has no effect over the "standard" file descriptors (stdin, stdout, stderr).

 

Since: 2.40

Property Details

The “argv” property

  “argv”                     GStrv

Argument vector.

Flags: Write / Construct Only


The “flags” property

  “flags”                    GSubprocessFlags

Subprocess flags.

Flags: Write / Construct Only

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