recent kernel return POLLERR and then calling read returns EGAIN which

leads to busy loop. Try to work around.

io/io_tryread.c

@@ -105,8 +105,10 @@ int64 io_tryread(int64 d,char* buf,int64 len) {
   if (!e->nonblock) {
     setitimer(ITIMER_REAL,&old,0);
   }
-  if (r==-1 && errno==EAGAIN)
+  if (r==-1 && errno==EAGAIN) {
+    if (e->goterror) r=-3;
     io_eagain_read(d);
+  }
   if (r==-1) {
     if (errno==EINTR) errno=EAGAIN;
     if (errno!=EAGAIN)

io/io_waituntil2.c

@@ -167,6 +167,7 @@ int64 io_waituntil2(int64 milliseconds) {
 	  /* error; signal whatever app is looking for */
 	  if (e->wantread) y[i].events|=POLLIN;
 	  if (e->wantwrite) y[i].events|=POLLOUT;
+	  e->goterror=1;	// prevent busy loop if the kernel return EAGAIN on read
 	}
 
 	newevents=0;

io_internal.h

@@ -49,6 +49,7 @@ typedef struct {
   unsigned int epolladded:1;
   unsigned int closed:1;	/* io_close called, but close deferred because of outstanding events */
   unsigned int zerocopy:1;	/* linux: setsockopt SO_ZEROCOPY done */
+  unsigned int goterror:1;	/* got POLLERR|POLLHUP */
 #ifdef __MINGW32__
   unsigned int readqueued:2;
   unsigned int writequeued:2;