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In POSIX-conformant operating systems, a process group denotes a collection of one or more processes. Process groups are used to control the distribution of signals. A signal directed to a process group is delivered individually to all of the processes that are members of the group. Process groups are themselves grouped into sessions. Process groups are not permitted to migrate from one session to another, and a process may only create new process groups belonging to the same session as it itself belongs to. Processes are not permitted to join process groups that are not in the same session as they themselves are. New process images created by a call to a function of the exec family inherit the process group membership and the session membership of the old process image.== Applications == The distribution of signals to process groups forms the basis of job control employed by shell programs. The tty device driver incorporates a notion of a foreground process group, to which it sends the SIGTSTP, SIGQUIT, and SIGINT signals generated by keyboard interrupts. It also sends the SIGTTIN and SIGTTOU signals to any processes that attempt to read from or write to the terminal and that are ''not'' in the foreground process group. The shell, in turn, partitions the command pipelines that it creates into process groups, and controls what process group is the foreground process group of its controlling terminal, thus determining what processes (and thus what command pipelines) may perform I/O to and from the terminal at any given time. When the shell forks a new child process for a command pipeline, both the parent shell process and the child process immediately attempt to make the process into the leader of the process group for the command pipeline. (They both attempt to do the same thing in order to avoid a race condition between the child becoming the process group leader, the child executing the program image of the command being executed, and the parent, or the tty device driver, attempting to send signals to the process group for job control. Unfortunately, this introduces another race, since the child may exit before the parent's attempt—the parent may thus set the wrong process as a group leader. The safest thing is to have the parent explicitly wait for the child to become a group leader by using vfork() or by communicating through a pipe.)Where a textual user interface is being used on a Unix-like system, sessions are used to implement login sessions. A single process, the session leader, interacts with the controlling terminal in order to ensure that all programs are terminated when a user "hangs up" the terminal connection. (Where a session leader is absent, the processes in the terminal's foreground process group are expected to handle hangups.) Where a graphical user interface is being used, the session concept is largely lost, and the kernel's notion of sessions largely ignored. Graphical user interfaces, such as where the X display manager is employed, use a different mechanism for implementing login sessions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「process group」の詳細全文を読む スポンサード リンク
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