Next: , Previous: , Up: Services   [Contents][Index]

4.4 Service De- and Constructors

All of the procedures listed below return procedures generated from the supplied arguments. These procedures take one argument in the case of destructors and no arguments in the case of constructors.

procedure: make-system-constructor command

The returned procedure will execute command in a shell and return #t if execution was successful, otherwise #f. For convenience, it takes multiple arguments which will be concatenated first.

procedure: make-system-destructor command

Similar to make-system-constructor, but returns #f if execution of the command was successful, #t if not.

procedure: make-forkexec-constructor command [#:directory (default-service-directory)] [#:environment-variables (default-environment-variables)]

Return a procedure that forks a child process, close all file descriptors except the standard output and standard error descriptors, sets the current directory to directory, changes the environment to environment-variables (using the environ procedure), and executes command (a list of strings.) Return the PID of the child process.

procedure: make-kill-destructor [signal]

Returns a procedure that sends signal to the pid which it takes as argument. This does work together with respawning services, because in that case the stop method of the <service> class sets the running slot to #f before actually calling the destructor; if it would not do that, killing the process in the destructor would immediately respawn the service.

The make-forkexec-constructor procedure builds upon the following procedures.

procedure: exec-command command [#:directory (default-service-directory)] [#:environment-variables (default-environment-variables)]
procedure: fork+exec-command command [#:directory (default-service-directory)] [#:environment-variables (default-environment-variables)]

Run command as the current process from directory, and with environment-variables (a list of strings like "PATH=/bin".) File descriptors 1 and 2 are kept as is, whereas file descriptor 0 (standard input) points to /dev/null; all other file descriptors are closed prior to yielding control to command.

fork+exec-command does the same, but in a separate process whose PID it returns.

Next: , Previous: , Up: Services   [Contents][Index]