[Qemu-devel] [PATCH 4/6] main-loop: interrupt wait when data arrives on a socket

[Paolo Bonzini <pbonzini@redhat.com>]

Right now, the main loop is not interrupted when data arrives on a
socket.  To fix this, register each socket to interrupt the main loop
with WSAEventSelect.  This does not replace select, it only communicates
a change in socket state that requires a select call.

Since the interrupt fires only once per recv call, or only once
after a send call returns EWOULDBLOCK we can activate it on all events
unconditionally.  If QEMU is momentarily uninterested on some condition,
the main loop will not busy wait.  Instead, it may get one extra wakeup,
but then it will ignore the condition until progress occurs and/or
qemu_set_fd_handler is called to set a callback.  At this point the
condition will be tested via select and the callback will be invoked
even if it is still disabled on the event.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 main-loop.c   |   69 ++++++++++++++++++++++++++++++++++++--------------------
 main-loop.h   |    1 +
 oslib-win32.c |    3 ++
 3 files changed, 48 insertions(+), 25 deletions(-)

diff --git a/main-loop.c b/main-loop.c
index dc6bdb5..7364074 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -392,10 +392,18 @@ void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
     }
 }
 
+void qemu_fd_register(int fd)
+{
+    WSAEventSelect(fd, qemu_event_handle, FD_READ | FD_ACCEPT | FD_CLOSE |
+                   FD_CONNECT | FD_WRITE | FD_OOB);
+}
+
 static int os_host_main_loop_wait(int timeout)
 {
     int ret, ret2, i;
     PollingEntry *pe;
+    int err;
+    WaitObjects *w = &wait_objects;
     static struct timeval tv0;
 
     /* XXX: need to suppress polling by better using win32 events */
@@ -403,38 +411,49 @@ static int os_host_main_loop_wait(int timeout)
     for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
         ret |= pe->func(pe->opaque);
     }
-    if (ret == 0) {
-        int err;
-        WaitObjects *w = &wait_objects;
+    if (ret != 0) {
+        return ret;
+    }
 
-        qemu_mutex_unlock_iothread();
-        ret = WaitForMultipleObjects(w->num, w->events, FALSE, timeout);
-        qemu_mutex_lock_iothread();
-        if (WAIT_OBJECT_0 + 0 <= ret && ret <= WAIT_OBJECT_0 + w->num - 1) {
-            if (w->func[ret - WAIT_OBJECT_0]) {
-                w->func[ret - WAIT_OBJECT_0](w->opaque[ret - WAIT_OBJECT_0]);
-            }
+    if (nfds >= 0) {
+        ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
+        if (ret != 0) {
+            timeout = 0;
+        }
+    }
 
-            /* Check for additional signaled events */
-            for (i = (ret - WAIT_OBJECT_0 + 1); i < w->num; i++) {
-                /* Check if event is signaled */
-                ret2 = WaitForSingleObject(w->events[i], 0);
-                if (ret2 == WAIT_OBJECT_0) {
-                    if (w->func[i]) {
-                        w->func[i](w->opaque[i]);
-                    }
-                } else if (ret2 != WAIT_TIMEOUT) {
-                    err = GetLastError();
-                    fprintf(stderr, "WaitForSingleObject error %d %d\n", i, err);
+    qemu_mutex_unlock_iothread();
+    ret = WaitForMultipleObjects(w->num, w->events, FALSE, timeout);
+    qemu_mutex_lock_iothread();
+    if (WAIT_OBJECT_0 + 0 <= ret && ret <= WAIT_OBJECT_0 + w->num - 1) {
+        if (w->func[ret - WAIT_OBJECT_0]) {
+            w->func[ret - WAIT_OBJECT_0](w->opaque[ret - WAIT_OBJECT_0]);
+        }
+
+        /* Check for additional signaled events */
+        for (i = (ret - WAIT_OBJECT_0 + 1); i < w->num; i++) {
+            /* Check if event is signaled */
+            ret2 = WaitForSingleObject(w->events[i], 0);
+            if (ret2 == WAIT_OBJECT_0) {
+                if (w->func[i]) {
+                    w->func[i](w->opaque[i]);
                 }
+            } else if (ret2 != WAIT_TIMEOUT) {
+                err = GetLastError();
+                fprintf(stderr, "WaitForSingleObject error %d %d\n", i, err);
             }
-        } else if (ret != WAIT_TIMEOUT) {
-            err = GetLastError();
-            fprintf(stderr, "WaitForMultipleObjects error %d %d\n", ret, err);
         }
+    } else if (ret != WAIT_TIMEOUT) {
+        err = GetLastError();
+        fprintf(stderr, "WaitForMultipleObjects error %d %d\n", ret, err);
     }
 
-    ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
+
+    /* If an edge-triggered socket event occurred, select will return a
+     * positive result on the next iteration.  We do not need to do anything
+     * here.
+     */
+
     return ret;
 }
 #endif
diff --git a/main-loop.h b/main-loop.h
index 4987041..e743aa0 100644
--- a/main-loop.h
+++ b/main-loop.h
@@ -359,6 +359,7 @@ void qemu_mutex_unlock_iothread(void);
 
 /* internal interfaces */
 
+void qemu_fd_register(int fd);
 void qemu_iohandler_fill(int *pnfds, fd_set *readfds, fd_set *writefds, fd_set *xfds);
 void qemu_iohandler_poll(fd_set *readfds, fd_set *writefds, fd_set *xfds, int rc);
 
diff --git a/oslib-win32.c b/oslib-win32.c
index ce3021e..ffbc6d0 100644
--- a/oslib-win32.c
+++ b/oslib-win32.c
@@ -28,6 +28,7 @@
 #include <windows.h>
 #include "config-host.h"
 #include "sysemu.h"
+#include "main-loop.h"
 #include "trace.h"
 #include "qemu_socket.h"
 
@@ -76,6 +77,7 @@ void qemu_vfree(void *ptr)
 void socket_set_block(int fd)
 {
     unsigned long opt = 0;
+    WSAEventSelect(fd, NULL, 0);
     ioctlsocket(fd, FIONBIO, &opt);
 }
 
@@ -83,6 +85,7 @@ void socket_set_nonblock(int fd)
 {
     unsigned long opt = 1;
     ioctlsocket(fd, FIONBIO, &opt);
+    qemu_fd_register(fd);
 }
 
 int inet_aton(const char *cp, struct in_addr *ia)
-- 
1.7.7.6