Fix the poor performance in network writing

The poor performance is hit when there is only one active port with a
big packet (> 64k bytes) to write. The network driver will split the
packet into 32k chunks, and only send the first chunk before returning
RD_PEND. When N_wait checks for signals from this port, it sees no
signal (write is not done yet), and thus the wait time is doubled, and
OS_Wait is called.

In OS_Wait, default Poll_Default is called, which goes through all
pending requests for the device. Because the packet is so big, after a
second "write", the packet is still not sent completely, and the status
remains the same: DR_PEND, which causes Poll_Default mistakenly thinks
the device is inactive, and then OS_Wait starts waiting with the doubled
wait time. The wait time could get doubled further until its max if the
packet is quite big.

The fix is in two folds:
1. Introduce a new flag RRF_ACTIVE, to mark the request as active in
case that partial data is written
2. Modify Poll_Default funcntion to check RRF_ACTIVE in
addition to the current DR_DONE/DR_ERROR.

So when the data is partial written, Poll_Default will return "TRUE",
which causes OS_Wait to return immediately, no matter how long the "wait
time" is.

Author: zsx

src/include/reb-device.h

@@ -93,6 +93,7 @@ enum {
 	RRF_PENDING,	// Request is attached to pending list
 	RRF_ALLOC,		// Request is allocated, not a temp on stack
 	RRF_WIDE,		// Wide char IO
+	RRF_ACTIVE,		// Port is active, even no new events yet
 };
 
 // REBOL Device Errors:

src/os/dev-net.c

@@ -460,6 +460,7 @@ static REBOOL Nonblocking_Mode(SOCKET sock)
 				Signal_Device(sock, EVT_WROTE);
 				return DR_DONE;
 			}
+			SET_FLAG(sock->flags, RRF_ACTIVE); /* notify OS_WAIT of activity */
 			return DR_PEND;
 		}
 		// if (result < 0) ...
@@ -612,7 +613,6 @@ static REBOOL Nonblocking_Mode(SOCKET sock)
 	return DR_PEND;
 }
 
-
 /***********************************************************************
 **
 **	Command Dispatch Table (RDC_ enum order)

src/os/host-device.c

@@ -102,9 +102,10 @@ static int Poll_Default(REBDEV *dev)
 	for (req = *prior; req; req = *prior) {
 
 		// Call command again:
-		if (req->command < RDC_MAX)
+		if (req->command < RDC_MAX) {
+			CLR_FLAG(req->flags, RRF_ACTIVE);
 			result = dev->commands[req->command](req);
-		else {
+		} else {
 			result = -1;	// invalid command, remove it
 			req->error = ((REBCNT)-1);
 		}
@@ -115,8 +116,12 @@ static int Poll_Default(REBDEV *dev)
 			req->next = 0;
 			CLR_FLAG(req->flags, RRF_PENDING);
 			change = TRUE;
+		} else {
+			prior = &req->next;
+			if (GET_FLAG(req->flags, RRF_ACTIVE)) {
+				change = TRUE;
+			}
 		}
-		else prior = &req->next;
 	}
 
 	return change;