unix- POSIX functionality

Portabilitynon-portable (requires POSIX)
Safe HaskellTrustworthy




POSIX signal support


The Signal type

Specific signals

Sending signals

raiseSignal :: Signal -> IO ()Source

raiseSignal int calls kill to signal the current process with interrupt signal int.

signalProcess :: Signal -> ProcessID -> IO ()Source

signalProcess int pid calls kill to signal process pid with interrupt signal int.

signalProcessGroup :: Signal -> ProcessGroupID -> IO ()Source

signalProcessGroup int pgid calls kill to signal all processes in group pgid with interrupt signal int.

Handling signals

data Handler Source

The actions to perform when a signal is received.


Catch (IO ()) 
CatchOnce (IO ()) 




:: Signal 
-> Handler 
-> Maybe SignalSet

other signals to block

-> IO Handler

old handler

installHandler int handler iset calls sigaction to install an interrupt handler for signal int. If handler is Default, SIG_DFL is installed; if handler is Ignore, SIG_IGN is installed; if handler is Catch action, a handler is installed which will invoke action in a new thread when (or shortly after) the signal is received. If iset is Just s, then the sa_mask of the sigaction structure is set to s; otherwise it is cleared. The previously installed signal handler for int is returned

Signal sets

reservedSignals :: SignalSetSource

A set of signals reserved for use by the implementation. In GHC, this will normally include either sigVTALRM or sigALRM.

The process signal mask

getSignalMask :: IO SignalSetSource

getSignalMask calls sigprocmask to determine the set of interrupts which are currently being blocked.

setSignalMask :: SignalSet -> IO ()Source

setSignalMask mask calls sigprocmask with SIG_SETMASK to block all interrupts in mask.

blockSignals :: SignalSet -> IO ()Source

blockSignals mask calls sigprocmask with SIG_BLOCK to add all interrupts in mask to the set of blocked interrupts.

unblockSignals :: SignalSet -> IO ()Source

unblockSignals mask calls sigprocmask with SIG_UNBLOCK to remove all interrupts in mask from the set of blocked interrupts.

The alarm timer

scheduleAlarm :: Int -> IO IntSource

scheduleAlarm i calls alarm to schedule a real time alarm at least i seconds in the future.

Waiting for signals

getPendingSignals :: IO SignalSetSource

getPendingSignals calls sigpending to obtain the set of interrupts which have been received but are currently blocked.

awaitSignal :: Maybe SignalSet -> IO ()Source

awaitSignal iset suspends execution until an interrupt is received. If iset is Just s, awaitSignal calls sigsuspend, installing s as the new signal mask before suspending execution; otherwise, it calls sigsuspend with current signal mask. Note that RTS scheduler signal (either virtualTimerExpired or realTimeAlarm) could cause premature termination of this call. It might be necessary to block that signal before invocation of awaitSignal with blockSignals reservedSignals.

awaitSignal returns when signal was received and processed by a signal handler, or if the signal could not be caught. If you have installed any signal handlers with installHandler, it may be wise to call yield directly after awaitSignal to ensure that the signal handler runs as promptly as possible.


setStoppedChildFlag :: Bool -> IO BoolSource

Tells the system whether or not to set the SA_NOCLDSTOP flag when installing new signal handlers.

queryStoppedChildFlag :: IO BoolSource

Queries the current state of the stopped child flag.