38 Processes

In the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process.

A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a “process". Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it.

In addition to processes that run programs, Lisp programs can open connections of several types to devices or processes running on the same machine or on other machines. The supported connection types are: TCP and UDP network connections, serial port connections, and pipe connections. Each such connection is also represented by a process object.

function processp object

This function returns t if object represents an Emacs process object, nil otherwise. The process object can represent a subprocess running a program or a connection of any supported type.

In addition to subprocesses of the current Emacs session, you can also access other processes running on your machine. See System Processes.

• Subprocess Creation		Functions that start subprocesses.
• Shell Arguments		Quoting an argument to pass it to a shell.
• Synchronous Processes		Details of using synchronous subprocesses.
• Asynchronous Processes		Starting up an asynchronous subprocess.
• Deleting Processes		Eliminating an asynchronous subprocess.
• Process Information		Accessing run-status and other attributes.
• Input to Processes		Sending input to an asynchronous subprocess.
• Signals to Processes		Stopping, continuing or interrupting an asynchronous subprocess.
• Output from Processes		Collecting output from an asynchronous subprocess.
• Sentinels		Sentinels run when process run-status changes.
• Query Before Exit		Whether to query if exiting will kill a process.
• System Processes		Accessing other processes running on your system.
• Transaction Queues		Transaction-based communication with subprocesses.
• Network		Opening network connections.
• Network Servers		Network servers let Emacs accept net connections.
• Datagrams		UDP network connections.
• Low-Level Network		Lower-level but more general function to create connections and servers.
• Misc Network		Additional relevant functions for net connections.
• Serial Ports		Communicating with serial ports.
• Byte Packing		Using bindat to pack and unpack binary data.