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(*
Title: Signal structure and signature.
Author: David Matthews
Copyright David Matthews 2000, 2008
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*)
signature SIGNAL =
sig
datatype sig_handle = SIG_DFL | SIG_IGN | SIG_HANDLE of int->unit
val signal: int * sig_handle -> sig_handle
end;
structure Signal: SIGNAL =
struct
datatype sig_handle = SIG_DFL | SIG_IGN | SIG_HANDLE of int->unit
local
val doSig = RunCall.run_call2 RuntimeCalls.POLY_SYS_signal_handler
in
fun signal(s, cmd) =
let
val c =
case cmd of
SIG_DFL => 0
| SIG_IGN => 1
| SIG_HANDLE f => RunCall.unsafeCast f
in
case doSig(0, (s, c)) of
0 => SIG_DFL
| 1 => SIG_IGN
| f => SIG_HANDLE(RunCall.unsafeCast f)
end
end
local
datatype sigHandle = SigHandle of (int->unit) * int | WeakMarker
val doSig = RunCall.run_call2 RuntimeCalls.POLY_SYS_signal_handler
open Thread
fun sigThread(): unit =
let
(* This call to the RTS returns either a pair of a signal
and a handler or a flag indicating that some wek reference
has been set to NONE. These aren't logically related but
it's convenient to use a single thread for both. *)
val nextSig: sigHandle = doSig(1, ())
(* When we get a WeakMarker message we need to broadcast
on this condition variable. *)
fun broadCastWeak haveLock () =
(
if haveLock then () else Mutex.lock Weak.weakLock;
ConditionVar.broadcast Weak.weakSignal;
Mutex.unlock Weak.weakLock
)
in
case nextSig of
SigHandle (handler, signal) => (handler signal handle _ => ())
| WeakMarker =>
(* If the lock is free we can do the broadcast now but
to avoid waiting and being unable to handle any signals
we fork off a thread if we can't. *)
if Mutex.trylock Weak.weakLock
then broadCastWeak true ()
else (Thread.fork(broadCastWeak false, []); ());
sigThread() (* Forever. *)
end
fun forkThread() =
(Thread.fork(sigThread, []); ()) handle Thread _ => print "Unable to create signal thread\n"
in
(* Run this thread now and also start one each time we start up. *)
val _ = forkThread()
val _ = PolyML.onEntry forkThread
end
end;
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