erts: Implement delay_send using timer instead of poll

The previous implementation uses a round-trip in the poll-set
to simulate a yield of the port context. With the poll thread
implementation this is no longer a good idea as it generated a
lot more work for the system. So this commit changes the
implementation to use a timer instead.

OTP-15471

1 files changed, 16 insertions, 4 deletions

diff --git a/erts/emulator/drivers/common/inet_drv.c b/erts/emulator/drivers/common/inet_drv.c
index 8a7cb7e6fa..627e1c8ec2 100644
--- a/erts/emulator/drivers/common/inet_drv.c
+++ b/erts/emulator/drivers/common/inet_drv.c
@@ -11250,6 +11250,12 @@ static int tcp_shutdown_error(tcp_descriptor* desc, int err)
     return tcp_send_or_shutdown_error(desc, err);
 }
 
+static void tcp_inet_delay_send(ErlDrvData data, ErlDrvTermData dummy)
+{
+    tcp_descriptor *desc = (tcp_descriptor*)data;
+    (void)tcp_inet_output(desc, INETP(desc)->s);
+}
+
 /*
 ** Send non-blocking vector data
 */
@@ -11319,7 +11325,10 @@ static int tcp_sendv(tcp_descriptor* desc, ErlIOVec* ev)
 	    INETP(desc)->is_ignored |= INET_IGNORE_WRITE;
 	    n = 0;
 	} else if (desc->tcp_add_flags & TCP_ADDF_DELAY_SEND) {
-	    n = 0;
+            driver_enqv(ix, ev, 0);
+            add_multi_timer(desc, INETP(desc)->port, 0,
+                            0, &tcp_inet_delay_send);
+	    return 0;
 	} else if (IS_SOCKET_ERROR(sock_sendv(desc->inet.s, ev->iov,
 					      vsize, &n, 0))) {
 	    if ((sock_errno() != ERRNO_BLOCK) && (sock_errno() != EINTR)) {
@@ -11816,6 +11825,12 @@ static int tcp_inet_output(tcp_descriptor* desc, HANDLE event)
 #ifdef __WIN32__
 		desc->inet.send_would_block = 1;
 #endif
+                /* If DELAY_SEND is set ready_output may have
+                   been called without doing select so we do
+                   a select in order to get into the correct
+                   state */
+                if (desc->tcp_add_flags & TCP_ADDF_DELAY_SEND)
+                    sock_select(INETP(desc), FD_WRITE, 1);
 		goto done;
 	    } else if (n == 0) { /* Workaround for redhat/CentOS 6.3 returning 
 				    0 when sending packets with 
@@ -12962,9 +12977,6 @@ static MultiTimerData *add_multi_timer(tcp_descriptor *desc, ErlDrvPort port,
     }
     /* Possibly set new timer */
     if (!s) {
-	if (mtd->next) {
-	    driver_cancel_timer(port);
-	}
 	driver_set_timer(port,timeout);
     }
     return mtd;