unix- POSIX functionality
Copyright(c) The University of Glasgow 2002
LicenseBSD-style (see the file libraries/base/LICENSE)
Portabilitynon-portable (requires POSIX)
Safe HaskellTrustworthy



POSIX signal support


The Signal type

Specific signals

sigABRT :: CInt Source #

Process abort signal.

sigALRM :: CInt Source #

Alarm clock.

sigBUS :: CInt Source #

Access to an undefined portion of a memory object.

sigCHLD :: CInt Source #

Child process terminated, stopped, or continued.

sigCONT :: CInt Source #

Continue executing, if stopped.

sigFPE :: CInt Source #

Erroneous arithmetic operation.

sigHUP :: CInt Source #


sigILL :: CInt Source #

Illegal instruction.

sigINT :: CInt Source #

Terminal interrupt signal.

sigKILL :: CInt Source #

Kill (cannot be caught or ignored).

sigPIPE :: CInt Source #

Write on a pipe with no one to read it.

sigQUIT :: CInt Source #

Terminal quit signal.

sigSEGV :: CInt Source #

Invalid memory reference.

sigSTOP :: CInt Source #

Stop executing (cannot be caught or ignored).

sigTERM :: CInt Source #

Termination signal.

sigTSTP :: CInt Source #

Terminal stop signal.

sigTTIN :: CInt Source #

Background process attempting read.

sigTTOU :: CInt Source #

Background process attempting write.

sigUSR1 :: CInt Source #

User-defined signal 1.

sigUSR2 :: CInt Source #

User-defined signal 2.

sigPOLL :: CInt Source #

Pollable event.

sigPROF :: CInt Source #

Profiling timer expired.

sigSYS :: CInt Source #

Bad system call.

sigTRAP :: CInt Source #

Trace/breakpoint trap.

sigURG :: CInt Source #

High bandwidth data is available at a socket.

sigVTALRM :: CInt Source #

Virtual timer expired.

sigXCPU :: CInt Source #

CPU time limit exceeded.

sigXFSZ :: CInt Source #

File size limit exceeded.

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.



Sets the disposition of the signal to SIG_DFL, which means we want the default action associated with the signal. For example, the default action for SIGTERM (and various other signals) is to terminate the process.


Set the disposition of the signal to SIG_IGN, which means we want to ignore the signal. Ignored signals will not be delivered to the process, and if also blocked will not be added to the pending set for later delivery (if/when unblocked). Some signals (e.g. SIGSTOP and SIGKILL) cannot be caught or ignored. not yet: | Hold

Catch (IO ())

signal handler is not reset

CatchOnce (IO ())

signal handler is automatically reset (via SA_RESETHAND)

CatchInfo (SignalInfo -> IO ())

Since: unix-

CatchInfoOnce (SignalInfo -> IO ())

Since: unix-

data SignalInfo Source #

Information about a received signal (derived from siginfo_t).

Since: unix-

data SignalSpecificInfo Source #

Information specific to a particular type of signal (derived from siginfo_t).

Since: unix-

installHandler Source #


:: 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 :: SignalSet Source #

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 SignalSet Source #

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 Int Source #

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

Waiting for signals

getPendingSignals :: IO SignalSet Source #

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 Bool Source #

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

queryStoppedChildFlag :: IO Bool Source #

Queries the current state of the stopped child flag.