Merge remote-tracking branch 'remotes/weil/tags/pull-wxx-20150924' into staging

wxx patch queue

# gpg: Signature made Thu 24 Sep 2015 20:24:50 BST using RSA key ID 677450AD
# gpg: Good signature from "Stefan Weil <sw@weilnetz.de>"
# gpg:                 aka "Stefan Weil <stefan.weil@weilnetz.de>"
# gpg:                 aka "Stefan Weil <stefan.weil@bib.uni-mannheim.de>"
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# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 4923 6FEA 75C9 5D69 8EC2  B78A E08C 21D5 6774 50AD

* remotes/weil/tags/pull-wxx-20150924:
  oslib-win32: only provide localtime_r/gmtime_r if missing
  gtk: avoid redefining _WIN32_WINNT macro
  qemu-thread: add a fast path to the Win32 QemuEvent
  slirp: Fix non blocking connect for w32
  nsis: Add QEMU version information to Windows registry

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 64 insertions, 4 deletions

diff --git a/util/oslib-win32.c b/util/oslib-win32.c
index 730a6707a0..08f5a9cda2 100644
--- a/util/oslib-win32.c
+++ b/util/oslib-win32.c
@@ -95,6 +95,7 @@ void qemu_anon_ram_free(void *ptr, size_t size)
     }
 }
 
+#ifndef CONFIG_LOCALTIME_R
 /* FIXME: add proper locking */
 struct tm *gmtime_r(const time_t *timep, struct tm *result)
 {
@@ -118,6 +119,7 @@ struct tm *localtime_r(const time_t *timep, struct tm *result)
     }
     return p;
 }
+#endif /* CONFIG_LOCALTIME_R */
 
 void qemu_set_block(int fd)
 {
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index 406b52f91d..6cdd553e9a 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -238,10 +238,34 @@ void qemu_sem_wait(QemuSemaphore *sem)
     }
 }
 
+/* Wrap a Win32 manual-reset event with a fast userspace path.  The idea
+ * is to reset the Win32 event lazily, as part of a test-reset-test-wait
+ * sequence.  Such a sequence is, indeed, how QemuEvents are used by
+ * RCU and other subsystems!
+ *
+ * Valid transitions:
+ * - free->set, when setting the event
+ * - busy->set, when setting the event, followed by futex_wake
+ * - set->free, when resetting the event
+ * - free->busy, when waiting
+ *
+ * set->busy does not happen (it can be observed from the outside but
+ * it really is set->free->busy).
+ *
+ * busy->free provably cannot happen; to enforce it, the set->free transition
+ * is done with an OR, which becomes a no-op if the event has concurrently
+ * transitioned to free or busy (and is faster than cmpxchg).
+ */
+
+#define EV_SET         0
+#define EV_FREE        1
+#define EV_BUSY       -1
+
 void qemu_event_init(QemuEvent *ev, bool init)
 {
     /* Manual reset.  */
-    ev->event = CreateEvent(NULL, TRUE, init, NULL);
+    ev->event = CreateEvent(NULL, TRUE, TRUE, NULL);
+    ev->value = (init ? EV_SET : EV_FREE);
 }
 
 void qemu_event_destroy(QemuEvent *ev)
@@ -251,17 +275,51 @@ void qemu_event_destroy(QemuEvent *ev)
 
 void qemu_event_set(QemuEvent *ev)
 {
-    SetEvent(ev->event);
+    if (atomic_mb_read(&ev->value) != EV_SET) {
+        if (atomic_xchg(&ev->value, EV_SET) == EV_BUSY) {
+            /* There were waiters, wake them up.  */
+            SetEvent(ev->event);
+        }
+    }
 }
 
 void qemu_event_reset(QemuEvent *ev)
 {
-    ResetEvent(ev->event);
+    if (atomic_mb_read(&ev->value) == EV_SET) {
+        /* If there was a concurrent reset (or even reset+wait),
+         * do nothing.  Otherwise change EV_SET->EV_FREE.
+         */
+        atomic_or(&ev->value, EV_FREE);
+    }
 }
 
 void qemu_event_wait(QemuEvent *ev)
 {
-    WaitForSingleObject(ev->event, INFINITE);
+    unsigned value;
+
+    value = atomic_mb_read(&ev->value);
+    if (value != EV_SET) {
+        if (value == EV_FREE) {
+            /* qemu_event_set is not yet going to call SetEvent, but we are
+             * going to do another check for EV_SET below when setting EV_BUSY.
+             * At that point it is safe to call WaitForSingleObject.
+             */
+            ResetEvent(ev->event);
+
+            /* Tell qemu_event_set that there are waiters.  No need to retry
+             * because there cannot be a concurent busy->free transition.
+             * After the CAS, the event will be either set or busy.
+             */
+            if (atomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
+                value = EV_SET;
+            } else {
+                value = EV_BUSY;
+            }
+        }
+        if (value == EV_BUSY) {
+            WaitForSingleObject(ev->event, INFINITE);
+        }
+    }
 }
 
 struct QemuThreadData {