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File name : forkfuns.hlp

Content :fork SYNOPSIS Create a new process via the fork system function USAGE Int_Type fork () DESCRIPTION The `fork' function creates a new child process via the `fork' system function. See the approriate documentation for the actual semantics involved such as what is preserved in the child process. Upon sucess, the function returns a value that is greater than 0 to the parent process that represents the child process's id. It will return 0 to the child process. If the fork function fails, a value of -1 will be returned and `errno' set accordingly. EXAMPLE The following example creates a child process to invoke the ``ls'' command on a Unix system. It also illustrates the low-level nature of the `fork' and related system calls. define ls () { variable pid = fork (); if (pid == -1) throw OSError, "fork failed: " + errno_string(errno); if ((pid == 0) && (-1 == execvp ("ls", ["ls", "-l"]))) { () = fprintf (stderr, "execvp failed: " + errno_string(errno)); _exit (1); } forever { variable status = waitpid (pid, 0); if (status == NULL) { if (errno == EINTR) continue; throw OSError, "waitpid failed: " + errno_string(errno); } return status.exit_status; } } SEE ALSO waitpid, execv, execvp, execve, _exit, system -------------------------------------------------------------- execve, execv, execvp SYNOPSIS Execute a new process USAGE Int_Type execve(path, argv[], envp[]) Int_Type execvp(path, argv[])} Int_Type execv(path, argv[])} DESCRIPTION The `execv' family of functions overlay the current process with a new process that corresponds to the program specified by the `path' argument. If for some reason the function fails, a value of -1 will be returned with `errno' set accordingly. Normally the function will not return. The `argv' parameter is an array of strings that will correspond to the argument list used when invoking the program. For example, if the invoked program is a C program, the `argv' parameter will correspond to the C program's argv-list. The `execve' function takes an array of strings that will be used to initialize the environment of the overlayed program. The `execvp' function will mimick the actions `/bin/sh' when searching for the executable file. NOTES These function are wrappers around the corresponding system library functions. See the system documentation for more information. SEE ALSO execve, execvp, system, fork, _exit -------------------------------------------------------------- _exit SYNOPSIS Exit the current processes USAGE _exit(Int_Type status) DESCRIPTION Like the related `exit' function, `_exit' may be used to terminate the current process. One of the differences between the two functions is that the `_exit' will not invoke various ``atexit'' handlers that are normally run when a program is terminated. See the system-specific C runtime library documentation for more information about this function. The main use of the `_exit' function is after the failure of one of the `execv' functions in a child process. SEE ALSO fork, execv, execvp, execve, waitpid, exit -------------------------------------------------------------- waitpid SYNOPSIS Wait for a specified process USAGE Struct_Type waitpid (pid, options) DESCRIPTION The `waitpid' function will cause the calling process to wait for the child process whose process id is `pid' to change its state, e.g., exit. It returns information about the process in the form of a structure with the following fields: pid The process-id of the child process, 0 if the process has not changed state. exited Non-zero if the child exited normally. exit_status The exit status of the child. This field is meaninful only if the exited field is non-zero. signal Non-zero of the child was terminated by a signal. The value of this field is that of the signal. coredump Non-zero if the child produced a core-dump as the result of termination by a signal. stopped Non-zero if the child was stopped via a signal. The value is that of the signal that stopped it. continued Non-zero if the process was continued. Upon error, the function will return NULL and set `errno' accordingly. The value of the `options' parameter is the bitwise-or of one of the following values: WNOHANG causes waitpid to return immediately if the child has not terminated. In this case, the value of the pid field will be 0 if the child is still running. WUNTRACED (see semantics in the OS documentation) WCONTINUED (see semantics in the OS documentation) EXAMPLE s = waitpid (pid, WNOHANG); if (s == NULL) throw OSError, "waitpid failed: " + errno_string (); if (s.pid == 0) message ("The child is still running"); else if (s.exited) vmessage ("child exited with status %d", s.exit_status); else if (s.signal) { vmessage ("child terminated by signal %d %s", s.signal, (s.coredump ? "(coredump)" : "")); } SEE ALSO fork, new_process --------------------------------------------------------------

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