114 lines
2.9 KiB
Plaintext
114 lines
2.9 KiB
Plaintext
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file implements runtime support for signal handling.
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//
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// Most synchronization primitives are not available from
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// the signal handler (it cannot block and cannot use locks)
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// so the handler communicates with a processing goroutine
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// via struct sig, below.
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//
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// Ownership for sig.Note passes back and forth between
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// the signal handler and the signal goroutine in rounds.
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// The initial state is that sig.note is cleared (setup by siginit).
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// At the beginning of each round, mask == 0.
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// The round goes through three stages:
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//
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// (In parallel)
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// 1a) One or more signals arrive and are handled
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// by sigsend using cas to set bits in sig.mask.
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// The handler that changes sig.mask from zero to non-zero
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// calls notewakeup(&sig).
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// 1b) Sigrecv calls notesleep(&sig) to wait for the wakeup.
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//
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// 2) Having received the wakeup, sigrecv knows that sigsend
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// will not send another wakeup, so it can noteclear(&sig)
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// to prepare for the next round. (Sigsend may still be adding
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// signals to sig.mask at this point, which is fine.)
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//
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// 3) Sigrecv uses cas to grab the current sig.mask and zero it,
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// triggering the next round.
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//
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// The signal handler takes ownership of the note by atomically
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// changing mask from a zero to non-zero value. It gives up
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// ownership by calling notewakeup. The signal goroutine takes
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// ownership by returning from notesleep (caused by the notewakeup)
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// and gives up ownership by clearing mask.
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package runtime
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#include "config.h"
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#include "runtime.h"
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#include "malloc.h"
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#include "defs.h"
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static struct {
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Note;
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uint32 mask;
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bool inuse;
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} sig;
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void
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siginit(void)
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{
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noteclear(&sig);
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}
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// Called from sighandler to send a signal back out of the signal handling thread.
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bool
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__go_sigsend(int32 s)
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{
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uint32 bit, mask;
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if(!sig.inuse)
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return false;
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bit = 1 << s;
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for(;;) {
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mask = sig.mask;
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if(mask & bit)
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break; // signal already in queue
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if(runtime_cas(&sig.mask, mask, mask|bit)) {
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// Added to queue.
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// Only send a wakeup for the first signal in each round.
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if(mask == 0)
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notewakeup(&sig);
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break;
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}
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}
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return true;
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}
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// Called to receive a bitmask of queued signals.
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func Sigrecv() (m uint32) {
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// runtime·entersyscall();
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notesleep(&sig);
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// runtime·exitsyscall();
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noteclear(&sig);
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for(;;) {
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m = sig.mask;
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if(runtime_cas(&sig.mask, m, 0))
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break;
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}
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}
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func Signame(sig int32) (name String) {
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const char* s = NULL;
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char buf[100];
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#if defined(HAVE_STRSIGNAL)
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s = strsignal(sig);
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#endif
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if (s == NULL) {
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snprintf(buf, sizeof buf, "signal %d", sig);
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s = buf;
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}
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int32 len = __builtin_strlen(s);
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unsigned char *data = runtime_mallocgc(len, FlagNoPointers, 0, 0);
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__builtin_memcpy(data, s, len);
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name.__data = data;
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name.__length = len;
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}
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func Siginit() {
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sig.inuse = true; // enable reception of signals; cannot disable
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}
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