Process handling [XL]

• fork() -> integer [XL]
• getpid() -> integer [XL]
• getppid() -> integer [XL]
• getuid() -> integer [XL]
• kill(p:integer) -> void [XL]
• on_fork :: property(open = 3) [XL]
• on_forked :: property(open = 3) [XL]
• process_status <: thing [XL]
• waitpid(p:integer) -> tuple(process_status, integer, any) [XL]
• waitpid(p:integer, block?:boolean) -> tuple(process_status, integer, any) [XL]

fork() -> integer

fork is the standard UNIX interface to create new processes. fork creates a child process that is an image of the current process that only differs by the returned value which is:

• 0 for the parent process
• n > 0 for the child process where n is the process id of the child

getpid() -> integer

getpid() returns the process id of the calling process

getppid() -> integer

getppid() returns the parent process id of the calling process

getuid() -> integer

getuid() returns the real user ID of the calling process. Under windows this method always returns 0

kill(p:integer) -> void

kill(p) terminates the process identified by the process id p. It first give a chance to the process to exit gracefully upon receipt of a SIGTERM signal. If the process still runs after a short timeout then a SIGKILL signal is send to the process. The caller should have necessary permissions.

on_fork :: property(open = 3)

fork, when called in CLAIRE applies all existing on_fork with the domain void. the on_fork callback is applied just before the fork, that is the parent process only. For instance :

on_fork() : void -> printf("attemp to fork...\n")

on_forked :: property(open = 3)

after a fork, CLAIRE applies all existing on_forked restrictions that have the domain boolean. the on_forked callback is applied with true from the child and false from the parent process. For instance :

on_forked(parent?:boolean) : void ->          printf("just forked (~I)\n",                      (if parent? princ("parent")                      else printf("child ~S", getpid())))

process_status <: thing

Instances

A process status is returned by waitpid and tell how a child process has exited:

• WRUNNING : the child still runs
• WEXITED : the child exited normally with a call to exit
• WSIGNALED : the child was terminated by a signal, this may be an abnormal termination that caused the creation a core dump file.
• WSTOPPED : the child was stopped

waitpid(p:integer) -> tuple(process_status, integer, any)

waitpid(p) is equivalent to waitpid(p, true)

waitpid(p:integer, block?:boolean) -> tuple(process_status, integer, any)

waitpid is a the UNIX interface to get status of child process. The parameter p specifies the set of child processes to wait for:

• p = -1 : the call waits for any child process.
• p = 0 : the call waits for any child process in the process group of the caller.
• p > 0 : the call waits for the process with process id p.
• else : the call waits for any process whose process group id equals the absolute value of p.