System.Posix.Process

forkProcess corresponds to the POSIX fork system call. The IO action passed as an argument is executed in the child process; no other threads will be copied to the child process. On success, forkProcess returns the child's ProcessID to the parent process; in case of an error, an exception is thrown.

forkProcess comes with a giant warning: since any other running threads are not copied into the child process, it's easy to go wrong: e.g. by accessing some shared resource that was held by another thread in the parent. Another example is the I/O manager thread: since the I/O manager isn't running in the child, attempting to do any Handle-based I/O will deadlock.

Using forkProcess in order to do executeFile is likely to work. Anything else: you're on your own.

executeFile

:: FilePath	Command
-> Bool	Search PATH?
-> [String]	Arguments
-> Maybe [(String, String)]	Environment
-> IO ()
`executeFile cmd args env` calls one of the `execv` family, depending on whether or not the current PATH is to be searched for the command, and whether or not an environment is provided to supersede the process's current environment. The basename (leading directory names suppressed) of the command is passed to `execv` as `arg[0]`; the argument list passed to `executeFile` therefore begins with `arg[1]`.

Exiting

exitImmediately :: ExitCode -> IO ()

exitImmediately status calls _exit to terminate the process with the indicated exit status. The operation never returns.

Process environment

getProcessID :: IO ProcessID

getProcessID calls getpid to obtain the ProcessID for the current process.

getParentProcessID :: IO ProcessID

getProcessID calls getppid to obtain the ProcessID for the parent of the current process.

getProcessGroupID :: IO ProcessGroupID

getProcessGroupID calls getpgrp to obtain the ProcessGroupID for the current process.

Process groups

createProcessGroup :: ProcessID -> IO ProcessGroupID

createProcessGroup pid calls setpgid to make process pid a new process group leader.

joinProcessGroup :: ProcessGroupID -> IO ()

joinProcessGroup pgid calls setpgid to set the ProcessGroupID of the current process to pgid.

setProcessGroupID :: ProcessID -> ProcessGroupID -> IO ()

setProcessGroupID pid pgid calls setpgid to set the ProcessGroupID for process pid to pgid.

Sessions

createSession :: IO ProcessGroupID

createSession calls setsid to create a new session with the current process as session leader.

Process times

data ProcessTimes

Constructors

ProcessTimes

elapsedTime :: ClockTick
userTime :: ClockTick
systemTime :: ClockTick
childUserTime :: ClockTick
childSystemTime :: ClockTick

getProcessTimes :: IO ProcessTimes

getProcessTimes calls times to obtain time-accounting information for the current process and its children.

Scheduling priority

nice :: Int -> IO ()

getProcessPriority :: ProcessID -> IO Int

getProcessGroupPriority :: ProcessGroupID -> IO Int

getUserPriority :: UserID -> IO Int

setProcessPriority :: ProcessID -> Int -> IO ()

setProcessGroupPriority :: ProcessGroupID -> Int -> IO ()

setUserPriority :: UserID -> Int -> IO ()

Process status

data ProcessStatus

Constructors

Exited ExitCode
Terminated Signal
Stopped Signal

Instances

Eq ProcessStatus

Ord ProcessStatus

Show ProcessStatus

getProcessStatus :: Bool -> Bool -> ProcessID -> IO (Maybe ProcessStatus)

getProcessStatus blk stopped pid calls waitpid, returning Just tc, the ProcessStatus for process pid if it is available, Nothing otherwise. If blk is False, then WNOHANG is set in the options for waitpid, otherwise not. If stopped is True, then WUNTRACED is set in the options for waitpid, otherwise not.

getAnyProcessStatus :: Bool -> Bool -> IO (Maybe (ProcessID, ProcessStatus))

getAnyProcessStatus blk stopped calls waitpid, returning Just (pid, tc), the ProcessID and ProcessStatus for any child process if one is available, Nothing otherwise. If blk is False, then WNOHANG is set in the options for waitpid, otherwise not. If stopped is True, then WUNTRACED is set in the options for waitpid, otherwise not.

getGroupProcessStatus :: Bool -> Bool -> ProcessGroupID -> IO (Maybe (ProcessID, ProcessStatus))

getGroupProcessStatus blk stopped pgid calls waitpid, returning Just (pid, tc), the ProcessID and ProcessStatus for any process in group pgid if one is available, Nothing otherwise. If blk is False, then WNOHANG is set in the options for waitpid, otherwise not. If stopped is True, then WUNTRACED is set in the options for waitpid, otherwise not.

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