uv_process_t — Process handle

Process handles will spawn a new process and allow the user to control it and establish communication channels with it using streams.

Data types

uv_process_t

Process handle type.

uv_process_options_t

Options for spawning the process (passed to uv_spawn().

typedef struct uv_process_options_s {
    uv_exit_cb exit_cb;
    const char* file;
    char** args;
    char** env;
    const char* cwd;
    unsigned int flags;
    int stdio_count;
    uv_stdio_container_t* stdio;
    uv_uid_t uid;
    uv_gid_t gid;
} uv_process_options_t;

void (*uv_exit_cb)(uv_process_t*, int64_t exit_status, int term_signal)

Type definition for callback passed in uv_process_options_t which will indicate the exit status and the signal that caused the process to terminate, if any.

uv_process_flags

Flags to be set on the flags field of uv_process_options_t.

enum uv_process_flags {
    /*
    * Set the child process' user id.
    */
    UV_PROCESS_SETUID = (1 << 0),
    /*
    * Set the child process' group id.
    */
    UV_PROCESS_SETGID = (1 << 1),
    /*
    * Do not wrap any arguments in quotes, or perform any other escaping, when
    * converting the argument list into a command line string. This option is
    * only meaningful on Windows systems. On Unix it is silently ignored.
    */
    UV_PROCESS_WINDOWS_VERBATIM_ARGUMENTS = (1 << 2),
    /*
    * Spawn the child process in a detached state - this will make it a process
    * group leader, and will effectively enable the child to keep running after
    * the parent exits. Note that the child process will still keep the
    * parent's event loop alive unless the parent process calls uv_unref() on
    * the child's process handle.
    */
    UV_PROCESS_DETACHED = (1 << 3),
    /*
    * Hide the subprocess console window that would normally be created. This
    * option is only meaningful on Windows systems. On Unix it is silently
    * ignored.
    */
    UV_PROCESS_WINDOWS_HIDE = (1 << 4)
};

uv_stdio_container_t

Container for each stdio handle or fd passed to a child process.

typedef struct uv_stdio_container_s {
    uv_stdio_flags flags;
    union {
        uv_stream_t* stream;
        int fd;
    } data;
} uv_stdio_container_t;

uv_stdio_flags

Flags specifying how a stdio should be transmitted to the child process.

typedef enum {
    UV_IGNORE = 0x00,
    UV_CREATE_PIPE = 0x01,
    UV_INHERIT_FD = 0x02,
    UV_INHERIT_STREAM = 0x04,
    /*
    * When UV_CREATE_PIPE is specified, UV_READABLE_PIPE and UV_WRITABLE_PIPE
    * determine the direction of flow, from the child process' perspective. Both
    * flags may be specified to create a duplex data stream.
    */
    UV_READABLE_PIPE = 0x10,
    UV_WRITABLE_PIPE = 0x20
} uv_stdio_flags;

Public members

uv_process_t.pid

The PID of the spawned process. It’s set after calling uv_spawn().

Note

The uv_handle_t members also apply.

uv_process_options_t.exit_cb

Callback called after the process exits.

uv_process_options_t.file

Path pointing to the program to be executed.

uv_process_options_t.args

Command line arguments. args[0] should be the path to the program. On Windows this uses CreateProcess which concatenates the arguments into a string this can cause some strange errors. See the UV_PROCESS_WINDOWS_VERBATIM_ARGUMENTS flag on uv_process_flags.

uv_process_options_t.env

Environment for the new process. If NULL the parents environment is used.

uv_process_options_t.cwd

Current working directory for the subprocess.

uv_process_options_t.flags

Various flags that control how uv_spawn() behaves. See uv_process_flags.

uv_process_options_t.stdio_count

uv_process_options_t.stdio

The stdio field points to an array of uv_stdio_container_t structs that describe the file descriptors that will be made available to the child process. The convention is that stdio[0] points to stdin, fd 1 is used for stdout, and fd 2 is stderr.

Note

On Windows file descriptors greater than 2 are available to the child process only if the child processes uses the MSVCRT runtime.

uv_process_options_t.uid

uv_process_options_t.gid

Libuv can change the child process’ user/group id. This happens only when the appropriate bits are set in the flags fields.

Note

This is not supported on Windows, uv_spawn() will fail and set the error to UV_ENOTSUP.

uv_stdio_container_t.flags

Flags specifying how the stdio container should be passed to the child. See uv_stdio_flags.

uv_stdio_container_t.data

Union containing either the stream or fd to be passed on to the child process.

API

void uv_disable_stdio_inheritance(void)

Disables inheritance for file descriptors / handles that this process inherited from its parent. The effect is that child processes spawned by this process don’t accidentally inherit these handles.

It is recommended to call this function as early in your program as possible, before the inherited file descriptors can be closed or duplicated.

Note

This function works on a best-effort basis: there is no guarantee that libuv can discover all file descriptors that were inherited. In general it does a better job on Windows than it does on Unix.

int uv_spawn(uv_loop_t* loop, uv_process_t* handle, const uv_process_options_t* options)

Initializes the process handle and starts the process. If the process is successfully spawned, this function will return 0. Otherwise, the negative error code corresponding to the reason it couldn’t spawn is returned.

Possible reasons for failing to spawn would include (but not be limited to) the file to execute not existing, not having permissions to use the setuid or setgid specified, or not having enough memory to allocate for the new process.

int uv_process_kill(uv_process_t* handle, int signum)

Sends the specified signal to the given process handle. Check the documentation on uv_signal_t — Signal handle for signal support, specially on Windows.

int uv_kill(int pid, int signum)

Sends the specified signal to the given PID. Check the documentation on uv_signal_t — Signal handle for signal support, specially on Windows.

See also

The uv_handle_t API functions also apply.