os/signal: new package

Fixes #71.

R=rsc, r
https://golang.org/cl/162056

src/pkg/Makefile

@@ -82,6 +82,7 @@ DIRS=\
 	net\
 	once\
 	os\
+	os/signal\
 	patch\
 	path\
 	rand\

src/pkg/os/signal/Makefile

@@ -0,0 +1,11 @@
+# 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.
+
+include ../../../Make.$(GOARCH)
+
+TARG=os/signal
+GOFILES=\
+	signal.go\
+
+include ../../../Make.pkg

src/pkg/os/signal/signal.go

@@ -0,0 +1,47 @@
+// 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.
+
+// Package signal implements operating system-independent signal handling.
+package signal
+
+import (
+	"runtime"
+	"strconv"
+)
+
+// A Signal can represent any operating system signal.
+type Signal interface {
+	String() string
+}
+
+type UnixSignal int32
+
+func (sig UnixSignal) String() string {
+	s := runtime.Signame(int32(sig))
+	if len(s) > 0 {
+		return s
+	}
+	return "Signal " + strconv.Itoa(int(sig))
+}
+
+// Incoming is the global signal channel.
+// All signals received by the program will be delivered to this channel.
+var Incoming <-chan Signal
+
+func process(ch chan<- Signal) {
+	for {
+		var mask uint32 = runtime.Sigrecv()
+		for sig := uint(0); sig < 32; sig++ {
+			if mask&(1<<sig) != 0 {
+				ch <- UnixSignal(sig)
+			}
+		}
+	}
+}
+
+func init() {
+	ch := make(chan Signal) // Done here so Incoming can have type <-chan Signal
+	Incoming = ch
+	go process(ch)
+}

src/pkg/os/signal/signal_test.go

@@ -0,0 +1,19 @@
+// 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.
+
+package signal
+
+import (
+	"syscall"
+	"testing"
+)
+
+func TestSignal(t *testing.T) {
+	// Send this process a SIGHUP.
+	syscall.Syscall(syscall.SYS_KILL, uintptr(syscall.Getpid()), syscall.SIGHUP, 0)
+
+	if sig := (<-Incoming).(UnixSignal); sig != 1 {
+		t.Error("signal was %v, want %v", sig, 1)
+	}
+}

src/pkg/runtime/Makefile

@@ -63,6 +63,7 @@ OFILES=\
 	rt0.$O\
 	sema.$O\
 	signal.$O\
+	sigqueue.$O\
 	slice.$O\
 	string.$O\
 	symtab.$O\
@@ -78,6 +79,7 @@ HFILES=\
 	malloc.h\
 	$(GOARCH)/asm.h\
 	$(GOOS)/os.h\
+	$(GOOS)/signals.h\
 	$(GOOS)/$(GOARCH)/defs.h\
 
 include ../../Make.pkg

src/pkg/runtime/darwin/386/signal.c

@@ -25,6 +25,14 @@ dumpregs(Regs *r)
 	printf("gs      %x\n", r->gs);
 }
 
+String
+signame(int32 sig)
+{
+	if(sig < 0 || sig >= NSIG)
+		return emptystring;
+	return gostring((byte*)sigtab[sig].name);
+}
+
 void
 sighandler(int32 sig, Siginfo *info, void *context)
 {
@@ -32,6 +40,11 @@ sighandler(int32 sig, Siginfo *info, void *context)
 	Mcontext *mc;
 	Regs *r;
 
+	if(sigtab[sig].flags & SigQueue) {
+		sigsend(sig);
+		return;
+	}
+
 	if(panicking)	// traceback already printed
 		exit(2);
 	panicking = 1;
@@ -82,12 +95,14 @@ initsig(void)
 	int32 i;
 	static Sigaction sa;
 
+	siginit();
+
 	sa.sa_flags |= SA_SIGINFO|SA_ONSTACK;
 	sa.sa_mask = 0xFFFFFFFFU;
 	sa.sa_tramp = sigtramp;	// sigtramp's job is to call into real handler
 	for(i = 0; i<NSIG; i++) {
 		if(sigtab[i].flags) {
-			if(sigtab[i].flags & SigCatch) {
+			if(sigtab[i].flags & (SigCatch | SigQueue)) {
 				sa.__sigaction_u.__sa_sigaction = sighandler;
 			} else {
 				sa.__sigaction_u.__sa_sigaction = sigignore;
@@ -100,4 +115,3 @@ initsig(void)
 		}
 	}
 }
-

src/pkg/runtime/darwin/amd64/signal.c

@@ -33,6 +33,14 @@ dumpregs(Regs *r)
 	printf("gs      %X\n", r->gs);
 }
 
+String
+signame(int32 sig)
+{
+	if(sig < 0 || sig >= NSIG)
+		return emptystring;
+	return gostring((byte*)sigtab[sig].name);
+}
+
 void
 sighandler(int32 sig, Siginfo *info, void *context)
 {
@@ -40,6 +48,11 @@ sighandler(int32 sig, Siginfo *info, void *context)
 	Mcontext *mc;
 	Regs *r;
 
+	if(sigtab[sig].flags & SigQueue) {
+		sigsend(sig);
+		return;
+	}
+
 	if(panicking)	// traceback already printed
 		exit(2);
 	panicking = 1;
@@ -90,12 +103,14 @@ initsig(void)
 	int32 i;
 	static Sigaction sa;
 
+	siginit();
+
 	sa.sa_flags |= SA_SIGINFO|SA_ONSTACK;
 	sa.sa_mask = 0xFFFFFFFFU;
 	sa.sa_tramp = sigtramp;	// sigtramp's job is to call into real handler
 	for(i = 0; i<NSIG; i++) {
 		if(sigtab[i].flags) {
-			if(sigtab[i].flags & SigCatch) {
+			if(sigtab[i].flags & (SigCatch | SigQueue)) {
 				sa.__sigaction_u.__sa_sigaction = sighandler;
 			} else {
 				sa.__sigaction_u.__sa_sigaction = sigignore;
@@ -108,4 +123,3 @@ initsig(void)
 		}
 	}
 }
-

src/pkg/runtime/darwin/signals.h

@@ -5,11 +5,12 @@
 #define C SigCatch
 #define I SigIgnore
 #define R SigRestart
+#define Q SigQueue
 
 static SigTab sigtab[] = {
 	/* 0 */	0, "SIGNONE: no trap",
-	/* 1 */	0, "SIGHUP: terminal line hangup",
-	/* 2 */	0, "SIGINT: interrupt",
+	/* 1 */	Q+R, "SIGHUP: terminal line hangup",
+	/* 2 */	Q+R, "SIGINT: interrupt",
 	/* 3 */	C, "SIGQUIT: quit",
 	/* 4 */	C, "SIGILL: illegal instruction",
 	/* 5 */	C, "SIGTRAP: trace trap",	/* used by panic and array out of bounds, etc. */
@@ -21,27 +22,28 @@ static SigTab sigtab[] = {
 	/* 11 */	C, "SIGSEGV: segmentation violation",
 	/* 12 */	C, "SIGSYS: bad system call",
 	/* 13 */	I, "SIGPIPE: write to broken pipe",
-	/* 14 */	0, "SIGALRM: alarm clock",
-	/* 15 */	0, "SIGTERM: termination",
-	/* 16 */	0, "SIGURG: urgent condition on socket",
+	/* 14 */	Q+R, "SIGALRM: alarm clock",
+	/* 15 */	Q+R, "SIGTERM: termination",
+	/* 16 */	Q+R, "SIGURG: urgent condition on socket",
 	/* 17 */	0, "SIGSTOP: stop",
-	/* 18 */	0, "SIGTSTP: keyboard stop",
+	/* 18 */	Q+R, "SIGTSTP: keyboard stop",
 	/* 19 */	0, "SIGCONT: continue after stop",
 	/* 20 */	I+R, "SIGCHLD: child status has changed",
-	/* 21 */	0, "SIGTTIN: background read from tty",
-	/* 22 */	0, "SIGTTOU: background write to tty",
-	/* 23 */	0, "SIGIO: i/o now possible",
-	/* 24 */	0, "SIGXCPU: cpu limit exceeded",
-	/* 25 */	0, "SIGXFSZ: file size limit exceeded",
-	/* 26 */	0, "SIGVTALRM: virtual alarm clock",
-	/* 27 */	0, "SIGPROF: profiling alarm clock",
-	/* 28 */	I+R, "SIGWINCH: window size change",
-	/* 29 */	0, "SIGINFO: status request from keyboard",
-	/* 30 */	0, "SIGUSR1: user-defined signal 1",
-	/* 31 */	0, "SIGUSR2: user-defined signal 2",
+	/* 21 */	Q+R, "SIGTTIN: background read from tty",
+	/* 22 */	Q+R, "SIGTTOU: background write to tty",
+	/* 23 */	Q+R, "SIGIO: i/o now possible",
+	/* 24 */	Q+R, "SIGXCPU: cpu limit exceeded",
+	/* 25 */	Q+R, "SIGXFSZ: file size limit exceeded",
+	/* 26 */	Q+R, "SIGVTALRM: virtual alarm clock",
+	/* 27 */	Q+R, "SIGPROF: profiling alarm clock",
+	/* 28 */	Q+R, "SIGWINCH: window size change",
+	/* 29 */	Q+R, "SIGINFO: status request from keyboard",
+	/* 30 */	Q+R, "SIGUSR1: user-defined signal 1",
+	/* 31 */	Q+R, "SIGUSR2: user-defined signal 2",
 };
 #undef C
 #undef I
 #undef R
+#undef Q
 
 #define	NSIG 32

src/pkg/runtime/extern.go

@@ -59,3 +59,10 @@ func Semacquire(s *uint32)
 // It is intended as a simple wakeup primitive for use by the synchronization
 // library and should not be used directly.
 func Semrelease(s *uint32)
+
+// Sigrecv returns a bitmask of signals that have arrived since the last call to Sigrecv.
+// It blocks until at least one signal arrives.
+func Sigrecv() uint32
+
+// Signame returns a string describing the signal, or "" if the signal is unknown.
+func Signame(sig int32) string

src/pkg/runtime/freebsd/386/signal.c

@@ -1,3 +1,7 @@
+// 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.
+
 #include "runtime.h"
 #include "defs.h"
 #include "signals.h"
@@ -32,12 +36,25 @@ dumpregs(Mcontext *r)
 	printf("gs      %x\n", r->mc_gs);
 }
 
+String
+signame(int32 sig)
+{
+	if(sig < 0 || sig >= NSIG)
+		return emptystring;
+	return gostring((byte*)sigtab[sig].name);
+}
+
 void
 sighandler(int32 sig, Siginfo* info, void* context)
 {
 	Ucontext *uc;
 	Mcontext *mc;
 
+	if(sigtab[sig].flags & SigQueue) {
+		sigsend(sig);
+		return;
+	}
+
 	if(panicking)	// traceback already printed
 		exit(2);
 	panicking = 1;
@@ -85,13 +102,15 @@ initsig(void)
 {
 	static Sigaction sa;
 
+	siginit();
+
 	int32 i;
 	sa.sa_flags |= SA_ONSTACK | SA_SIGINFO;
 	sa.sa_mask = ~0x0ull;
 	
 	for(i = 0; i < NSIG; i++) {
 		if(sigtab[i].flags) {
-			if(sigtab[i].flags & SigCatch)
+			if(sigtab[i].flags & (SigCatch | SigQueue))
 				sa.__sigaction_u.__sa_sigaction = (void*) sigtramp;
 			else
 				sa.__sigaction_u.__sa_sigaction = (void*) sigignore;

src/pkg/runtime/freebsd/amd64/signal.c

@@ -1,3 +1,7 @@
+// 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.
+
 #include "runtime.h"
 #include "defs.h"
 #include "signals.h"
@@ -40,12 +44,25 @@ dumpregs(Mcontext *r)
 	printf("gs      %X\n", r->mc_gs);
 }
 
+String
+signame(int32 sig)
+{
+	if(sig < 0 || sig >= NSIG)
+		return emptystring;
+	return gostring((byte*)sigtab[sig].name);
+}
+
 void
 sighandler(int32 sig, Siginfo* info, void* context)
 {
 	Ucontext *uc;
 	Mcontext *mc;
 
+	if(sigtab[sig].flags & SigQueue) {
+		sigsend(sig);
+		return;
+	}
+
 	if(panicking)	// traceback already printed
 		exit(2);
 	panicking = 1;
@@ -93,13 +110,15 @@ initsig(void)
 {
 	static Sigaction sa;
 
+	siginit();
+
 	int32 i;
 	sa.sa_flags |= SA_ONSTACK | SA_SIGINFO;
 	sa.sa_mask = ~0x0ull;
 	
 	for(i = 0; i < NSIG; i++) {
 		if(sigtab[i].flags) {
-			if(sigtab[i].flags & SigCatch)
+			if(sigtab[i].flags & (SigCatch | SigQueue))
 				sa.__sigaction_u.__sa_sigaction = (void*) sigtramp;
 			else
 				sa.__sigaction_u.__sa_sigaction = (void*) sigignore;

src/pkg/runtime/freebsd/signals.h

@@ -5,11 +5,12 @@
 #define C SigCatch
 #define I SigIgnore
 #define R SigRestart
+#define Q SigQueue
 
 static SigTab sigtab[] = {
 	/* 0 */		0, "SIGNONE: no trap",
-	/* 1 */		0, "SIGHUP: terminal line hangup",
-	/* 2 */		0, "SIGINT: interrupt",
+	/* 1 */		Q+R, "SIGHUP: terminal line hangup",
+	/* 2 */		Q+R, "SIGINT: interrupt",
 	/* 3 */		C, "SIGQUIT: quit",
 	/* 4 */		C, "SIGILL: illegal instruction",
 	/* 5 */		C, "SIGTRAP: trace trap",
@@ -21,28 +22,29 @@ static SigTab sigtab[] = {
 	/* 11 */	C, "SIGSEGV: segmentation violation",
 	/* 12 */	C, "SIGSYS: bad system call",
 	/* 13 */	I, "SIGPIPE: write to broken pipe",
-	/* 14 */	0, "SIGALRM: alarm clock",
-	/* 15 */	0, "SIGTERM: termination",
-	/* 16 */	0, "SIGURG: urgent condition on socket",
+	/* 14 */	Q+R, "SIGALRM: alarm clock",
+	/* 15 */	Q+R, "SIGTERM: termination",
+	/* 16 */	Q+R, "SIGURG: urgent condition on socket",
 	/* 17 */	0, "SIGSTOP: stop, unblockable",
-	/* 18 */	0, "SIGTSTP: stop from tty",
+	/* 18 */	Q+R, "SIGTSTP: stop from tty",
 	/* 19 */	0, "SIGCONT: continue",
 	/* 20 */	I+R, "SIGCHLD: child status has changed",
-	/* 21 */	0, "SIGTTIN: background read from tty",
-	/* 22 */	0, "SIGTTOU: background write to tty",
-	/* 23 */	0, "SIGIO: i/o now possible",
-	/* 24 */	0, "SIGXCPU: cpu limit exceeded",
-	/* 25 */	0, "SIGXFSZ: file size limit exceeded",
-	/* 26 */	0, "SIGVTALRM: virtual alarm clock",
-	/* 27 */	0, "SIGPROF: profiling alarm clock",
+	/* 21 */	Q+R, "SIGTTIN: background read from tty",
+	/* 22 */	Q+R, "SIGTTOU: background write to tty",
+	/* 23 */	Q+R, "SIGIO: i/o now possible",
+	/* 24 */	Q+R, "SIGXCPU: cpu limit exceeded",
+	/* 25 */	Q+R, "SIGXFSZ: file size limit exceeded",
+	/* 26 */	Q+R, "SIGVTALRM: virtual alarm clock",
+	/* 27 */	Q+R, "SIGPROF: profiling alarm clock",
 	/* 28 */	I+R, "SIGWINCH: window size change",
-	/* 29 */	0, "SIGINFO: information request",
-	/* 30 */	0, "SIGUSR1: user-defined signal 1",
-	/* 31 */	0, "SIGUSR2: user-defined signal 2",
-	/* 32 */	0, "SIGTHR: reserved",
+	/* 29 */	Q+R, "SIGINFO: information request",
+	/* 30 */	Q+R, "SIGUSR1: user-defined signal 1",
+	/* 31 */	Q+R, "SIGUSR2: user-defined signal 2",
+	/* 32 */	Q+R, "SIGTHR: reserved",
 };
 #undef C
 #undef I
 #undef R
+#undef Q
 
 #define	NSIG 33

src/pkg/runtime/linux/386/signal.c

@@ -33,12 +33,25 @@ extern void sigtramp(void);
 extern void sigignore(void);	// just returns
 extern void sigreturn(void);	// calls sigreturn
 
+String
+signame(int32 sig)
+{
+	if(sig < 0 || sig >= NSIG)
+		return emptystring;
+	return gostring((byte*)sigtab[sig].name);
+}
+
 void
 sighandler(int32 sig, Siginfo* info, void* context)
 {
 	Ucontext *uc;
 	Sigcontext *sc;
 
+	if(sigtab[sig].flags & SigQueue) {
+		sigsend(sig);
+		return;
+	}
+
 	if(panicking)	// traceback already printed
 		exit(2);
 	panicking = 1;
@@ -81,13 +94,15 @@ initsig(void)
 {
 	static Sigaction sa;
 
+	siginit();
+
 	int32 i;
 	sa.sa_flags = SA_ONSTACK | SA_SIGINFO | SA_RESTORER;
 	sa.sa_mask = 0xFFFFFFFFFFFFFFFFULL;
 	sa.sa_restorer = (void*)sigreturn;
 	for(i = 0; i<NSIG; i++) {
 		if(sigtab[i].flags) {
-			if(sigtab[i].flags & SigCatch)
+			if(sigtab[i].flags & (SigCatch | SigQueue))
 				sa.k_sa_handler = (void*)sigtramp;
 			else
 				sa.k_sa_handler = (void*)sigignore;
@@ -99,4 +114,3 @@ initsig(void)
 		}
 	}
 }
-

src/pkg/runtime/linux/amd64/signal.c

@@ -41,6 +41,14 @@ extern void sigtramp(void);
 extern void sigignore(void);	// just returns
 extern void sigreturn(void);	// calls sigreturn
 
+String
+signame(int32 sig)
+{
+	if(sig < 0 || sig >= NSIG)
+		return emptystring;
+	return gostring((byte*)sigtab[sig].name);
+}
+
 void
 sighandler(int32 sig, Siginfo* info, void* context)
 {
@@ -48,6 +56,11 @@ sighandler(int32 sig, Siginfo* info, void* context)
 	Mcontext *mc;
 	Sigcontext *sc;
 
+	if(sigtab[sig].flags & SigQueue) {
+		sigsend(sig);
+		return;
+	}
+
 	if(panicking)	// traceback already printed
 		exit(2);
 	panicking = 1;
@@ -91,13 +104,15 @@ initsig(void)
 {
 	static Sigaction sa;
 
+	siginit();
+
 	int32 i;
 	sa.sa_flags = SA_ONSTACK | SA_SIGINFO | SA_RESTORER;
 	sa.sa_mask = 0xFFFFFFFFFFFFFFFFULL;
 	sa.sa_restorer = (void*)sigreturn;
 	for(i = 0; i<NSIG; i++) {
 		if(sigtab[i].flags) {
-			if(sigtab[i].flags & SigCatch)
+			if(sigtab[i].flags & (SigCatch | SigQueue))
 				sa.sa_handler = (void*)sigtramp;
 			else
 				sa.sa_handler = (void*)sigignore;
@@ -109,4 +124,3 @@ initsig(void)
 		}
 	}
 }
-

src/pkg/runtime/linux/arm/signal.c

@@ -35,6 +35,14 @@ extern void sigtramp(void);
 extern void sigignore(void);	// just returns
 extern void sigreturn(void);	// calls sigreturn
 
+String
+signame(int32 sig)
+{
+	if(sig < 0 || sig >= NSIG)
+		return emptystring;
+	return gostring((byte*)sigtab[sig].name);
+}
+
 void sighandler(void) {}
 // void
 // sighandler(int32 sig, Siginfo* info, void* context)

src/pkg/runtime/linux/signals.h

@@ -5,11 +5,12 @@
 #define C SigCatch
 #define I SigIgnore
 #define R SigRestart
+#define Q SigQueue
 
 static SigTab sigtab[] = {
 	/* 0 */	0, "SIGNONE: no trap",
-	/* 1 */	0, "SIGHUP: terminal line hangup",
-	/* 2 */	0, "SIGINT: interrupt",
+	/* 1 */	Q+R, "SIGHUP: terminal line hangup",
+	/* 2 */	Q+R, "SIGINT: interrupt",
 	/* 3 */	C, "SIGQUIT: quit",
 	/* 4 */	C, "SIGILL: illegal instruction",
 	/* 5 */	C, "SIGTRAP: trace trap",
@@ -17,31 +18,32 @@ static SigTab sigtab[] = {
 	/* 7 */	C, "SIGBUS: bus error",
 	/* 8 */	C, "SIGFPE: floating-point exception",
 	/* 9 */	0, "SIGKILL: kill",
-	/* 10 */	0, "SIGUSR1: user-defined signal 1",
+	/* 10 */	Q+R, "SIGUSR1: user-defined signal 1",
 	/* 11 */	C, "SIGSEGV: segmentation violation",
-	/* 12 */	0, "SIGUSR2: user-defined signal 2",
+	/* 12 */	Q+R, "SIGUSR2: user-defined signal 2",
 	/* 13 */	I, "SIGPIPE: write to broken pipe",
-	/* 14 */	0, "SIGALRM: alarm clock",
-	/* 15 */	0, "SIGTERM: termination",
-	/* 16 */	0, "SIGSTKFLT: stack fault",
-	/* 17 */	I+R, "SIGCHLD: child status has changed",
+	/* 14 */	Q+R, "SIGALRM: alarm clock",
+	/* 15 */	Q+R, "SIGTERM: termination",
+	/* 16 */	Q+R, "SIGSTKFLT: stack fault",
+	/* 17 */	Q+R, "SIGCHLD: child status has changed",
 	/* 18 */	0, "SIGCONT: continue",
 	/* 19 */	0, "SIGSTOP: stop, unblockable",
-	/* 20 */	0, "SIGTSTP: keyboard stop",
-	/* 21 */	0, "SIGTTIN: background read from tty",
-	/* 22 */	0, "SIGTTOU: background write to tty",
-	/* 23 */	0, "SIGURG: urgent condition on socket",
-	/* 24 */	0, "SIGXCPU: cpu limit exceeded",
-	/* 25 */	0, "SIGXFSZ: file size limit exceeded",
-	/* 26 */	0, "SIGVTALRM: virtual alarm clock",
-	/* 27 */	0, "SIGPROF: profiling alarm clock",
-	/* 28 */	I+R, "SIGWINCH: window size change",
-	/* 29 */	0, "SIGIO: i/o now possible",
-	/* 30 */	0, "SIGPWR: power failure restart",
+	/* 20 */	Q+R, "SIGTSTP: keyboard stop",
+	/* 21 */	Q+R, "SIGTTIN: background read from tty",
+	/* 22 */	Q+R, "SIGTTOU: background write to tty",
+	/* 23 */	Q+R, "SIGURG: urgent condition on socket",
+	/* 24 */	Q+R, "SIGXCPU: cpu limit exceeded",
+	/* 25 */	Q+R, "SIGXFSZ: file size limit exceeded",
+	/* 26 */	Q+R, "SIGVTALRM: virtual alarm clock",
+	/* 27 */	Q+R, "SIGPROF: profiling alarm clock",
+	/* 28 */	Q+R, "SIGWINCH: window size change",
+	/* 29 */	Q+R, "SIGIO: i/o now possible",
+	/* 30 */	Q+R, "SIGPWR: power failure restart",
 	/* 31 */	C, "SIGSYS: bad system call",
 };
 #undef C
 #undef I
 #undef R
+#undef Q
 
 #define	NSIG 32

src/pkg/runtime/proc.c

@@ -527,12 +527,9 @@ gosched(void)
 // Record that it's not using the cpu anymore.
 // This is called only from the go syscall library, not
 // from the low-level system calls used by the runtime.
-// The "arguments" are syscall.Syscall's stack frame
 void
-runtime·entersyscall(uint64 callerpc, int64 trap)
+runtime·entersyscall(void)
 {
-	USED(callerpc, trap);
-
 	lock(&sched);
 	if(sched.predawn) {
 		unlock(&sched);

src/pkg/runtime/runtime.h

@@ -235,6 +235,7 @@ enum
 	SigCatch = 1<<0,
 	SigIgnore = 1<<1,
 	SigRestart = 1<<2,
+	SigQueue = 1<<3,
 };
 
 // (will be) shared with go; edit ../cmd/6g/sys.go too.
@@ -373,6 +374,10 @@ void	breakpoint(void);
 void	gosched(void);
 void	goexit(void);
 void	runcgo(void (*fn)(void*), void*);
+void	entersyscall(void);
+void	exitsyscall(void);
+void	siginit(void);
+void	sigsend(int32 sig);
 
 #pragma	varargck	argpos	printf	1
 
@@ -485,6 +490,8 @@ float64	ldexp(float64 d, int32 e);
 float64	modf(float64 d, float64 *ip);
 void	semacquire(uint32*);
 void	semrelease(uint32*);
+String	signame(int32 sig);
+
 
 void	mapassign(Hmap*, byte*, byte*);
 void	mapaccess(Hmap*, byte*, byte*, bool*);

src/pkg/runtime/sigqueue.cgo

@@ -0,0 +1,90 @@
+// 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 and cannot use locks)
+// so the handler communicates with a processing goroutine
+// via struct sig, below.
+//
+// Ownership for sig.Note passes back and forth between
+// the signal handler and the signal goroutine in rounds.
+// The initial state is that sig.note is cleared (setup by siginit).
+// At the beginning of each round, mask == 0.
+// The round goes through three stages:
+//
+// (In parallel)
+// 1a) One or more signals arrive and are handled
+// by sigsend using cas to set bits in sig.mask.
+// The handler that changes sig.mask from zero to non-zero
+// calls notewakeup(&sig).
+// 1b) Sigrecv calls notesleep(&sig) to wait for the wakeup.
+//
+// 2) Having received the wakeup, sigrecv knows that sigsend
+// will not send another wakeup, so it can noteclear(&sig)
+// to prepare for the next round. (Sigsend may still be adding
+// signals to sig.mask at this point, which is fine.)
+//
+// 3) Sigrecv uses cas to grab the current sig.mask and zero it,
+// triggering the next round.
+//
+// The signal handler takes ownership of the note by atomically
+// changing mask from a zero to non-zero value. It gives up
+// ownership by calling notewakeup. The signal goroutine takes
+// ownership by returning from notesleep (caused by the notewakeup)
+// and gives up ownership by clearing mask.
+
+package runtime
+#include "runtime.h"
+#include "defs.h"
+
+static struct {
+	Note;
+	uint32 mask;
+} sig;
+
+void
+siginit(void)
+{
+	noteclear(&sig);
+}
+
+// Called from sighandler to send a signal back out of the signal handling thread.
+void
+sigsend(int32 s)
+{
+	uint32 bit, mask;
+
+	bit = 1 << s;
+	for(;;) {
+		mask = sig.mask;
+		if(mask & bit)
+			return;		// signal already in queue
+		if(cas(&sig.mask, mask, mask|bit)) {
+			// Added to queue.
+			// Only send a wakeup for the first signal in each round.
+			if(mask == 0)
+				notewakeup(&sig);
+			return;
+		}
+	}
+}
+
+// Called to receive a bitmask of queued signals.
+func Sigrecv() (m uint32) {
+	runtime·entersyscall();
+	notesleep(&sig);
+	runtime·exitsyscall();
+	noteclear(&sig);
+	for(;;) {
+		m = sig.mask;
+		if(cas(&sig.mask, m, 0))
+			break;
+	}
+}
+
+func Signame(sig int32) (name String) {
+	name = signame(sig);
+}