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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements runtime support for signal handling.
//
// Most synchronization primitives are not available from
// the signal handler (it cannot block, allocate memory, or use locks)
// so the handler communicates with a processing goroutine
// via struct sig, below.
//
// sigsend() is called by the signal handler to queue a new signal.
// signal_recv() is called by the Go program to receive a newly queued signal.
// Synchronization between sigsend() and signal_recv() is based on the sig.state
// variable. It can be in 3 states: 0, HASWAITER and HASSIGNAL.
// HASWAITER means that signal_recv() is blocked on sig.Note and there are no
// new pending signals.
// HASSIGNAL means that sig.mask *may* contain new pending signals,
// signal_recv() can't be blocked in this state.
// 0 means that there are no new pending signals and signal_recv() is not blocked.
// Transitions between states are done atomically with CAS.
// When signal_recv() is unblocked, it resets sig.Note and rechecks sig.mask.
// If several sigsend()'s and signal_recv() execute concurrently, it can lead to
// unnecessary rechecks of sig.mask, but must not lead to missed signals
// nor deadlocks.
package signal
#include "config.h"
#include "runtime.h"
#include "arch.h"
#include "malloc.h"
#include "defs.h"
static struct {
Note;
uint32 mask[(NSIG+31)/32];
uint32 wanted[(NSIG+31)/32];
uint32 state;
bool inuse;
} sig;
enum {
HASWAITER = 1,
HASSIGNAL = 2,
};
// Called from sighandler to send a signal back out of the signal handling thread.
bool
__go_sigsend(int32 s)
{
uint32 bit, mask, old, new;
if(!sig.inuse || s < 0 || (size_t)s >= 32*nelem(sig.wanted) || !(sig.wanted[s/32]&(1U<<(s&31))))
return false;
bit = 1 << (s&31);
for(;;) {
mask = sig.mask[s/32];
if(mask & bit)
break; // signal already in queue
if(runtime_cas(&sig.mask[s/32], mask, mask|bit)) {
// Added to queue.
// Only send a wakeup if the receiver needs a kick.
for(;;) {
old = runtime_atomicload(&sig.state);
if(old == HASSIGNAL)
break;
if(old == HASWAITER)
new = 0;
else // if(old == 0)
new = HASSIGNAL;
if(runtime_cas(&sig.state, old, new)) {
if (old == HASWAITER)
runtime_notewakeup(&sig);
break;
}
}
break;
}
}
return true;
}
// Called to receive the next queued signal.
// Must only be called from a single goroutine at a time.
func signal_recv() (m uint32) {
static uint32 recv[nelem(sig.mask)];
uint32 i, old, new;
for(;;) {
// Serve from local copy if there are bits left.
for(i=0; i<NSIG; i++) {
if(recv[i/32]&(1U<<(i&31))) {
recv[i/32] ^= 1U<<(i&31);
m = i;
goto done;
}
}
// Check and update sig.state.
for(;;) {
old = runtime_atomicload(&sig.state);
if(old == HASWAITER)
runtime_throw("inconsistent state in signal_recv");
if(old == HASSIGNAL)
new = 0;
else // if(old == 0)
new = HASWAITER;
if(runtime_cas(&sig.state, old, new)) {
if (new == HASWAITER) {
runtime_entersyscall();
runtime_notesleep(&sig);
runtime_exitsyscall();
runtime_noteclear(&sig);
}
break;
}
}
// Get a new local copy.
for(i=0; (size_t)i<nelem(sig.mask); i++) {
for(;;) {
m = sig.mask[i];
if(runtime_cas(&sig.mask[i], m, 0))
break;
}
recv[i] = m;
}
}
done:;
// goc requires that we fall off the end of functions
// that return values instead of using our own return
// statements.
}
// Must only be called from a single goroutine at a time.
func signal_enable(s uint32) {
int32 i;
if(!sig.inuse) {
// The first call to signal_enable is for us
// to use for initialization. It does not pass
// signal information in m.
sig.inuse = true; // enable reception of signals; cannot disable
runtime_noteclear(&sig);
return;
}
if(~s == 0) {
// Special case: want everything.
for(i=0; (size_t)i<nelem(sig.wanted); i++)
sig.wanted[i] = ~(uint32)0;
runtime_sigenable(s);
return;
}
if(s >= nelem(sig.wanted)*32)
return;
sig.wanted[s/32] |= 1U<<(s&31);
runtime_sigenable(s);
}
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