runtime: refactor level-triggered IO support

Remove GOOS_solaris ifdef from netpoll code,
instead introduce runtime edge/level triggered IO flag.
Replace armread/armwrite with a single arm(mode) function,
that's how all other interfaces look like and these functions
will need to do roughly the same thing anyway.

LGTM=rsc
R=golang-codereviews, dave, rsc
CC=golang-codereviews
https://golang.org/cl/55500044

src/pkg/runtime/netpoll.goc

@@ -134,12 +134,9 @@ ret:
 func runtime_pollWait(pd *PollDesc, mode int) (err int) {
 	err = checkerr(pd, mode);
 	if(err == 0) {
-#ifdef GOOS_solaris
-		if(mode == 'r')
-			runtime·netpollarmread(pd->fd);
-		else if(mode == 'w')
-			runtime·netpollarmwrite(pd->fd);
-#endif
+		// As for now only Solaris uses level-triggered IO.
+		if(Solaris)
+			runtime·netpollarm(pd->fd, mode);
 		while(!netpollblock(pd, mode, false)) {
 			err = checkerr(pd, mode);
 			if(err != 0)
@@ -152,13 +149,8 @@ func runtime_pollWait(pd *PollDesc, mode int) (err int) {
 }
 
 func runtime_pollWaitCanceled(pd *PollDesc, mode int) {
-#ifdef GOOS_solaris
-	if(mode == 'r')
-		runtime·netpollarmread(pd->fd);
-	else if(mode == 'w')
-		runtime·netpollarmwrite(pd->fd);
-#endif
-	// wait for ioready, ignore closing or timeouts.
+	// This function is used only on windows after a failed attempt to cancel
+	// a pending async IO operation. Wait for ioready, ignore closing or timeouts.
 	while(!netpollblock(pd, mode, true))
 		;
 }

src/pkg/runtime/netpoll_epoll.c

@@ -52,6 +52,13 @@ runtime·netpollclose(uintptr fd)
 	return -res;
 }
 
+void
+runtime·netpollarm(uintptr fd, int32 mode)
+{
+	USED(fd, mode);
+	runtime·throw("unused");
+}
+
 // polls for ready network connections
 // returns list of goroutines that become runnable
 G*

src/pkg/runtime/netpoll_kqueue.c

@@ -59,6 +59,13 @@ runtime·netpollclose(uintptr fd)
 	return 0;
 }
 
+void
+runtime·netpollarm(uintptr fd, int32 mode)
+{
+	USED(fd, mode);
+	runtime·throw("unused");
+}
+
 // Polls for ready network connections.
 // Returns list of goroutines that become runnable.
 G*

src/pkg/runtime/netpoll_windows.c

@@ -72,6 +72,13 @@ runtime·netpollclose(uintptr fd)
 	return 0;
 }
 
+void
+runtime·netpollarm(uintptr fd, int32 mode)
+{
+	USED(fd, mode);
+	runtime·throw("unused");
+}
+
 // Polls for completed network IO.
 // Returns list of goroutines that become runnable.
 G*

src/pkg/runtime/runtime.h

@@ -893,8 +893,7 @@ int32	runtime·netpollopen(uintptr, PollDesc*);
 int32   runtime·netpollclose(uintptr);
 void	runtime·netpollready(G**, PollDesc*, int32);
 uintptr	runtime·netpollfd(PollDesc*);
-void	runtime·netpollarmread(uintptr fd);
-void	runtime·netpollarmwrite(uintptr fd);
+void	runtime·netpollarm(uintptr, int32);
 void	runtime·crash(void);
 void	runtime·parsedebugvars(void);
 void	_rt0_go(void);