change NetworkClock to cache the offset and do lazy evaluation, but m…

…ake sure the offset is rediscovered periodically.
derekzhang79 · Nov 5, 2010 · 3a1c894 · 3a1c894
1 parent 85fa9d6
commit 3a1c894
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Showing 3 changed files with 29 additions and 20 deletions.
diff --git a/Classes/NetworkClock.h b/Classes/NetworkClock.h
@@ -13,6 +13,7 @@
 @interface NetworkClock : NSObject {
 
     NSTimeInterval          timeIntervalSinceDeviceTime;
+    NSDate *                timeLastSynchronized;
 
     NSMutableArray *        timeAssociations;
 

diff --git a/Classes/NetworkClock.m b/Classes/NetworkClock.m
@@ -22,30 +22,38 @@ - (id) init {
     if (nil == [super init]) return nil;
 
     timeAssociations = [[NSMutableArray arrayWithCapacity:48] retain];
-    timeIntervalSinceDeviceTime = 0.0;
+    timeLastSynchronized = [[NSDate dateWithTimeIntervalSince1970:0.0] retain];
 
     return self;
 }
 
 /*┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
-  ┃ Scan the associations and get the best time offset, then return adjusted time                    ┃
+  ┃ Return the device clock time adjusted for the offset to network-derived UTC.  If we have not     ┃
+  ┃ synchronized for five minutes, get a new offset by scanning the associations.                    ┃
   ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛*/
 - (NSDate *) networkTime {
-    short       usefulCount = 0;
-    timeIntervalSinceDeviceTime = 0.0;
+    if ([timeLastSynchronized timeIntervalSinceNow] < -90.0) {
+        [timeLastSynchronized release];
 
-    for (NetAssociation * timeAssociation in timeAssociations) {
-        if (timeAssociation.useful) {
-            usefulCount++;
-            timeIntervalSinceDeviceTime += timeAssociation.offset;
+        short       usefulCount = 0;
+        timeIntervalSinceDeviceTime = 0.0;
+
+        for (NetAssociation * timeAssociation in timeAssociations) {
+            if (timeAssociation.useful) {
+                usefulCount++;
+                timeIntervalSinceDeviceTime += timeAssociation.offset;
+            }
         }
-    }
-
-    if (usefulCount == 0)
-        NSLog(@"no useful associations");
-    else {
-        timeIntervalSinceDeviceTime /= usefulCount;
-    }
+
+        if (usefulCount == 0)
+            NSLog(@"no useful associations");
+        else {
+            NSLog(@"%i useful associations", usefulCount);
+            timeIntervalSinceDeviceTime /= usefulCount;
+        }
+
+        timeLastSynchronized = [[NSDate date] retain];
+    }    
 
     return [[NSDate date] dateByAddingTimeInterval:-timeIntervalSinceDeviceTime];
 }
@@ -160,4 +168,4 @@ - (NSString *) hostAddress:(struct sockaddr_in *) sockAddr {
 
 SYNTHESIZE_SINGLETON_FOR_CLASS(NetworkClock);
 
-@end
+@end
diff --git a/Classes/ntpAAppDelegate.m b/Classes/ntpAAppDelegate.m
@@ -23,8 +23,8 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
     [window makeKeyAndVisible];
 
     NSTimer * repeatingTimer = [[NSTimer alloc] 
-                                initWithFireDate:[NSDate dateWithTimeIntervalSinceNow:1.0]
-                                        interval:30.0
+                                initWithFireDate:[NSDate dateWithTimeIntervalSinceNow:10.0]
+                                        interval:10.0
                                           target:self 
                                         selector:@selector(repeatingMethod:)
                                         userInfo:nil 
@@ -37,8 +37,8 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
 }
 
 - (void) repeatingMethod:(NSTimer*) theTimer {
-    NSLog(@"clock: %@", [NSDate date]);
-    NSLog(@"timer: %@", [[NetworkClock sharedNetworkClock] networkTime]);
+    NSLog(@"sys clock: %@", [NSDate date]);
+    NSLog(@"net clock: %@", [[NetworkClock sharedNetworkClock] networkTime]);
 }
 
 - (void)applicationWillTerminate:(UIApplication *)application {