Avoid use of CFAbsoluteTime as much as possible.

SPDY.xcodeproj/project.pbxproj

@@ -94,11 +94,18 @@
 		5C2229591952257800CAF160 /* SPDYURLRequestTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 5C2229581952257800CAF160 /* SPDYURLRequestTest.m */; };
 		5C2A211D19F9CA0E00D0EA76 /* SPDYLoggingTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 5C2A211C19F9CA0E00D0EA76 /* SPDYLoggingTest.m */; };
 		5C427F0F1A1C7C4D0072403D /* SPDYSenTestLog.m in Sources */ = {isa = PBXBuildFile; fileRef = 5C427F0E1A1C7C4D0072403D /* SPDYSenTestLog.m */; };
+		5C427F111A1D57890072403D /* SPDYStopwatchTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 5C427F101A1D57890072403D /* SPDYStopwatchTest.m */; };
 		5CF0A2C91A089BC500B6D141 /* SPDYMetadataTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 5CF0A2C81A089BC500B6D141 /* SPDYMetadataTest.m */; };
 		5CF0A2CC1A0952D900B6D141 /* SPDYMockURLProtocolClient.m in Sources */ = {isa = PBXBuildFile; fileRef = 5CF0A2CB1A0952D900B6D141 /* SPDYMockURLProtocolClient.m */; };
 		7774C1318AB029C6BCEF84D6 /* SPDYSessionTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 7774C2026A4DE9957D75F629 /* SPDYSessionTest.m */; };
 		7774C1F1E544793907908882 /* SPDYMockFrameEncoderDelegate.m in Sources */ = {isa = PBXBuildFile; fileRef = 7774C69089A6978113F0C275 /* SPDYMockFrameEncoderDelegate.m */; };
+		7774C868441241542B0A90C0 /* SPDYStopwatch.m in Sources */ = {isa = PBXBuildFile; fileRef = 7774CE34A3AA067D98DA7ECC /* SPDYStopwatch.m */; };
 		7774CA1FA1F4A59CA0906BB7 /* SPDYSocket+SPDYSocketMock.m in Sources */ = {isa = PBXBuildFile; fileRef = 7774C0ECD0C6E5D73FB38752 /* SPDYSocket+SPDYSocketMock.m */; };
+		7774CC29BBD86413798C1425 /* SPDYStopwatch.h in Headers */ = {isa = PBXBuildFile; fileRef = 7774CE030BB898D2BE3D320D /* SPDYStopwatch.h */; };
+		7774CD12A73EA9ABAE521441 /* SPDYStopwatch.m in Sources */ = {isa = PBXBuildFile; fileRef = 7774CE34A3AA067D98DA7ECC /* SPDYStopwatch.m */; };
+		7774CD9416661E40D76713F5 /* SPDYStopwatch.h in Headers */ = {isa = PBXBuildFile; fileRef = 7774CE030BB898D2BE3D320D /* SPDYStopwatch.h */; };
+		7774CDD84A5D07F8DE5B8684 /* SPDYStopwatch.m in Sources */ = {isa = PBXBuildFile; fileRef = 7774CE34A3AA067D98DA7ECC /* SPDYStopwatch.m */; };
+		7774CF887055793F373F0D5E /* SPDYStopwatch.h in Headers */ = {isa = PBXBuildFile; fileRef = 7774CE030BB898D2BE3D320D /* SPDYStopwatch.h */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
@@ -152,6 +159,7 @@
 		5C2229581952257800CAF160 /* SPDYURLRequestTest.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYURLRequestTest.m; sourceTree = "<group>"; };
 		5C2A211C19F9CA0E00D0EA76 /* SPDYLoggingTest.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYLoggingTest.m; sourceTree = "<group>"; };
 		5C427F0E1A1C7C4D0072403D /* SPDYSenTestLog.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYSenTestLog.m; sourceTree = "<group>"; };
+		5C427F101A1D57890072403D /* SPDYStopwatchTest.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYStopwatchTest.m; sourceTree = "<group>"; };
 		5CF0A2C81A089BC500B6D141 /* SPDYMetadataTest.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYMetadataTest.m; sourceTree = "<group>"; };
 		5CF0A2CA1A0952BA00B6D141 /* SPDYMockURLProtocolClient.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SPDYMockURLProtocolClient.h; sourceTree = "<group>"; };
 		5CF0A2CB1A0952D900B6D141 /* SPDYMockURLProtocolClient.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYMockURLProtocolClient.m; sourceTree = "<group>"; };
@@ -160,6 +168,8 @@
 		7774C69089A6978113F0C275 /* SPDYMockFrameEncoderDelegate.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYMockFrameEncoderDelegate.m; sourceTree = "<group>"; };
 		7774C7E1AF717FC36B7F15B6 /* SPDYSocket+SPDYSocketMock.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "SPDYSocket+SPDYSocketMock.h"; sourceTree = "<group>"; };
 		7774CD0A3295C8E314D6E3FF /* SPDYMockFrameEncoderDelegate.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SPDYMockFrameEncoderDelegate.h; sourceTree = "<group>"; };
+		7774CE030BB898D2BE3D320D /* SPDYStopwatch.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SPDYStopwatch.h; sourceTree = "<group>"; };
+		7774CE34A3AA067D98DA7ECC /* SPDYStopwatch.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SPDYStopwatch.m; sourceTree = "<group>"; };
 		D2CC14B216179B43002E37CF /* Foundation.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = Foundation.framework; path = System/Library/Frameworks/Foundation.framework; sourceTree = SDKROOT; };
 		D2CC14B816179B43002E37CF /* SPDY-Prefix.pch */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "SPDY-Prefix.pch"; sourceTree = "<group>"; };
 		D2CC14C01618CF62002E37CF /* SPDYProtocol.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SPDYProtocol.h; sourceTree = "<group>"; };
@@ -234,6 +244,7 @@
 				0679F3CE186217FC006F122E /* SPDYOriginTest.m */,
 				25959A3E1937DE3900FC9731 /* SPDYSessionManagerTest.m */,
 				7774C2026A4DE9957D75F629 /* SPDYSessionTest.m */,
+				5C427F101A1D57890072403D /* SPDYStopwatchTest.m */,
 				060C235D17CE9FCE000B4E9C /* SPDYStreamManagerTest.m */,
 				067EBFE617418F350029F16C /* SPDYStreamTest.m */,
 				5C2229581952257800CAF160 /* SPDYURLRequestTest.m */,
@@ -320,8 +331,8 @@
 				D2CC14B816179B43002E37CF /* SPDY-Prefix.pch */,
 				062EA63E175D4CD3003BC1CE /* SPDYCommonLogger.h */,
 				062EA63F175D4CD3003BC1CE /* SPDYCommonLogger.m */,
-				06811C961714D426000D1677 /* SPDYError.h */,
 				062EA63C175D1A15003BC1CE /* SPDYDefinitions.h */,
+				06811C961714D426000D1677 /* SPDYError.h */,
 				D2CC14C9161A25CC002E37CF /* SPDYFrame.h */,
 				D2CC14CA161A25CC002E37CF /* SPDYFrame.m */,
 				D2CC14C6161A1952002E37CF /* SPDYFrameDecoder.h */,
@@ -333,6 +344,8 @@
 				4FE891C7065B348CC7EF4BFC /* SPDYHeaderBlockDecompressor.h */,
 				4FE895BE087AC28BBBC857F9 /* SPDYHeaderBlockDecompressor.m */,
 				06811C9A1715DC85000D1677 /* SPDYLogger.h */,
+				0655606619D5EDA600631121 /* SPDYMetadata.h */,
+				0655606719D5EDA600631121 /* SPDYMetadata.m */,
 				06B290CC1861018900540A03 /* SPDYOrigin.h */,
 				06B290CD1861018900540A03 /* SPDYOrigin.m */,
 				D2CC14C01618CF62002E37CF /* SPDYProtocol.h */,
@@ -343,16 +356,16 @@
 				D2CC14CD161A5826002E37CF /* SPDYSessionManager.m */,
 				06FC94121694B92400FC95DF /* SPDYSettingsStore.h */,
 				06FC94131694B92400FC95DF /* SPDYSettingsStore.m */,
-				069D0E88167F9D010037D8AF /* SPDYStream.h */,
-				069D0E89167F9D010037D8AF /* SPDYStream.m */,
 				D2CC14CF161A9EE9002E37CF /* SPDYSocket.h */,
 				D2CC14D0161A9EE9002E37CF /* SPDYSocket.m */,
+				7774CE030BB898D2BE3D320D /* SPDYStopwatch.h */,
+				7774CE34A3AA067D98DA7ECC /* SPDYStopwatch.m */,
+				069D0E88167F9D010037D8AF /* SPDYStream.h */,
+				069D0E89167F9D010037D8AF /* SPDYStream.m */,
 				061C8E9217C5954400D22083 /* SPDYStreamManager.h */,
 				061C8E9317C5954400D22083 /* SPDYStreamManager.m */,
 				06E7BF111823B74D004DB65D /* SPDYTLSTrustEvaluator.h */,
 				06290990169E497300E35A82 /* SPDYZLibCommon.h */,
-				0655606619D5EDA600631121 /* SPDYMetadata.h */,
-				0655606719D5EDA600631121 /* SPDYMetadata.m */,
 			);
 			path = SPDY;
 			sourceTree = "<group>";
@@ -370,6 +383,7 @@
 				0540DAAF19CB802600673796 /* SPDYTLSTrustEvaluator.h in Headers */,
 				0540DAAC19CB7FF900673796 /* SPDYError.h in Headers */,
 				0540DAA919CB7FEB00673796 /* SPDYCommonLogger.h in Headers */,
+				7774CD9416661E40D76713F5 /* SPDYStopwatch.h in Headers */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -383,6 +397,7 @@
 				05C7CEBB19CB45820032D681 /* SPDYProtocol.h in Headers */,
 				05C7CEBC19CB458F0032D681 /* SPDYTLSTrustEvaluator.h in Headers */,
 				0540DAAA19CB7FEB00673796 /* SPDYCommonLogger.h in Headers */,
+				7774CC29BBD86413798C1425 /* SPDYStopwatch.h in Headers */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -396,6 +411,7 @@
 				06E7BF131824371F004DB65D /* SPDYTLSTrustEvaluator.h in Headers */,
 				06811C971714D426000D1677 /* SPDYError.h in Headers */,
 				062EA640175D4CD3003BC1CE /* SPDYCommonLogger.h in Headers */,
+				7774CF887055793F373F0D5E /* SPDYStopwatch.h in Headers */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -580,6 +596,7 @@
 				5CF0A2C91A089BC500B6D141 /* SPDYMetadataTest.m in Sources */,
 				060C235E17CE9FCE000B4E9C /* SPDYStreamManagerTest.m in Sources */,
 				0655606819D5EDA600631121 /* SPDYMetadata.m in Sources */,
+				5C427F111A1D57890072403D /* SPDYStopwatchTest.m in Sources */,
 				06290995169E4D9700E35A82 /* SPDYHeaderBlockCompressor.m in Sources */,
 				06FDA21216717DF100137DBD /* SPDYHeaderBlockDecompressor.m in Sources */,
 				5C2229591952257800CAF160 /* SPDYURLRequestTest.m in Sources */,
@@ -599,6 +616,7 @@
 				5C427F0F1A1C7C4D0072403D /* SPDYSenTestLog.m in Sources */,
 				7774CA1FA1F4A59CA0906BB7 /* SPDYSocket+SPDYSocketMock.m in Sources */,
 				7774C1318AB029C6BCEF84D6 /* SPDYSessionTest.m in Sources */,
+				7774CD12A73EA9ABAE521441 /* SPDYStopwatch.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -622,6 +640,7 @@
 				062EA643175D4CD3003BC1CE /* SPDYCommonLogger.m in Sources */,
 				061C8E9617C5954400D22083 /* SPDYStreamManager.m in Sources */,
 				06B290CF1861018A00540A03 /* SPDYOrigin.m in Sources */,
+				7774C868441241542B0A90C0 /* SPDYStopwatch.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -645,6 +664,7 @@
 				062EA645175D4CD3003BC1CE /* SPDYCommonLogger.m in Sources */,
 				061C8E9817C5954400D22083 /* SPDYStreamManager.m in Sources */,
 				06B290D21861018A00540A03 /* SPDYOrigin.m in Sources */,
+				7774CDD84A5D07F8DE5B8684 /* SPDYStopwatch.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

SPDY/SPDYMetadata.m

@@ -9,9 +9,9 @@
 //  Created by Michael Schore
 //
 
-#import "SPDYCommonLogger.h"
 #import "SPDYMetadata.h"
 #import "SPDYProtocol.h"
+#import "SPDYStopwatch.h"
 
 @implementation SPDYMetadata
 {
@@ -71,7 +71,7 @@ - (id)init
         _hostPort = 0;
 
         NSUInteger ptr = (NSUInteger)self;
-        CFAbsoluteTime timestamp = CFAbsoluteTimeGetCurrent();
+        SPDYTimeInterval timestamp = [SPDYStopwatch currentSystemTime];
         _identifier = [NSString stringWithFormat:@"%f/%tx", timestamp, ptr];
 
         dispatch_barrier_async(__identifiersQueue, ^{

SPDY/SPDYSession.m

@@ -20,16 +20,14 @@
 #import "SPDYCommonLogger.h"
 #import "SPDYFrameDecoder.h"
 #import "SPDYFrameEncoder.h"
+#import "SPDYMetadata.h"
 #import "SPDYOrigin.h"
 #import "SPDYProtocol.h"
-#import "SPDYSession.h"
-#import "SPDYSessionManager.h"
 #import "SPDYSettingsStore.h"
 #import "SPDYSocket.h"
+#import "SPDYStopwatch.h"
 #import "SPDYStream.h"
 #import "SPDYStreamManager.h"
-#import "SPDYTLSTrustEvaluator.h"
-#import "SPDYMetadata.h"
 
 // The input buffer should be more than twice MAX_CHUNK_LENGTH and
 // MAX_COMPRESSED_HEADER_BLOCK_LENGTH to avoid having to resize the
@@ -59,9 +57,8 @@ @implementation SPDYSession
     NSMutableData *_inputBuffer;
 
     SPDYStreamId _lastGoodStreamId;
-    CFAbsoluteTime _lastSocketActivity;
-    CFAbsoluteTime _sessionPingOut;
-    CFTimeInterval _sessionLatency;
+    SPDYStopwatch *_sessionPingStopwatch;
+    SPDYTimeInterval _sessionLatency;
     NSUInteger _bufferReadIndex;
     NSUInteger _bufferWriteIndex;
     uint32_t _initialSendWindowSize;
@@ -78,7 +75,7 @@ @implementation SPDYSession
     bool _established;
     bool _receivedGoAwayFrame;
     bool _sentGoAwayFrame;
-    CFAbsoluteTime _connectedTime;
+    SPDYStopwatch *_connectedStopwatch;
     NSString *_connectedHost;
     in_port_t _connectedPort;
 }
@@ -103,6 +100,9 @@ - (id)initWithOrigin:(SPDYOrigin *)origin
             return nil;
         }
 
+        _sessionPingStopwatch = [[SPDYStopwatch alloc] init];
+        _connectedStopwatch = [[SPDYStopwatch alloc] init];
+
         SPDYSocket *socket = [[SPDYSocket alloc] initWithDelegate:self];
         bool connecting = [socket connectToHost:origin.host
                                          onPort:origin.port
@@ -193,7 +193,7 @@ - (void)openStream:(SPDYStream *)stream
     if (_sessionLatency >= 0) {
         stream.metadata.latencyMs = (NSInteger)(_sessionLatency * 1000);
     }
-    stream.metadata.connectedMs = (CFAbsoluteTimeGetCurrent() - _connectedTime) * 1000;
+    stream.metadata.connectedMs = _connectedStopwatch.elapsedSeconds * 1000;
     stream.metadata.hostAddress = _connectedHost;
     stream.metadata.hostPort = _connectedPort;
 
@@ -284,14 +284,12 @@ - (void)_closeWithStatus:(SPDYSessionStatus)status
 
 - (bool)socket:(SPDYSocket *)socket securedWithTrust:(SecTrustRef)trust
 {
-    _lastSocketActivity = CFAbsoluteTimeGetCurrent();
     return [SPDYProtocol evaluateServerTrust:trust forHost:_origin.host];
 }
 
 - (void)socket:(SPDYSocket *)socket didConnectToHost:(NSString *)host port:(in_port_t)port
 {
-    _lastSocketActivity = CFAbsoluteTimeGetCurrent();
-    _connectedTime = _lastSocketActivity;
+    [_connectedStopwatch reset];
     SPDY_INFO(@"session connected to %@ (%@:%u)", _origin, host, port);
 
     _connected = YES;
@@ -309,7 +307,6 @@ - (void)socket:(SPDYSocket *)socket didConnectToHost:(NSString *)host port:(in_p
 
 - (void)socket:(SPDYSocket *)socket didReadData:(NSData *)data withTag:(long)tag
 {
-    _lastSocketActivity = CFAbsoluteTimeGetCurrent();
     SPDY_DEBUG(@"socket read[%li] (%lu)", tag, (unsigned long)data.length);
 
     _bufferWriteIndex += data.length;
@@ -343,9 +340,8 @@ - (void)socket:(SPDYSocket *)socket didReadData:(NSData *)data withTag:(long)tag
 
 - (void)socket:(SPDYSocket *)socket didWriteDataWithTag:(long)tag
 {
-    _lastSocketActivity = CFAbsoluteTimeGetCurrent();
     if (tag == 1) {
-        _sessionPingOut = _lastSocketActivity;
+        [_sessionPingStopwatch reset];
     }
 }
 
@@ -361,12 +357,10 @@ - (void)socket:(SPDYSocket *)socket didWriteDataWithTag:(long)tag
 
 - (void)socket:(SPDYSocket *)socket didWritePartialDataOfLength:(NSUInteger)partialLength tag:(long)tag
 {
-    _lastSocketActivity = CFAbsoluteTimeGetCurrent();
 }
 
 - (void)socket:(SPDYSocket *)socket willDisconnectWithError:(NSError *)error
 {
-    _lastSocketActivity = CFAbsoluteTimeGetCurrent();
     SPDY_WARNING(@"session connection error: %@", error);
     for (SPDYStream *stream in _activeStreams) {
         stream.delegate = nil;
@@ -377,7 +371,6 @@ - (void)socket:(SPDYSocket *)socket willDisconnectWithError:(NSError *)error
 
 - (void)socketDidDisconnect:(SPDYSocket *)socket
 {
-    _lastSocketActivity = CFAbsoluteTimeGetCurrent();
     SPDY_INFO(@"session connection closed");
 
     _connected = NO;
@@ -600,6 +593,12 @@ - (void)didReadSynReplyFrame:(SPDYSynReplyFrame *)synReplyFrame frameDecoder:(SP
 
     stream.metadata.rxBytes += synReplyFrame.encodedLength;
 
+    // While we prefer to record latencyMs at stream open time, the ping response may not have been
+    // received yet. It will have been received by this point however.
+    if (_sessionLatency >= 0 && stream.metadata.latencyMs <= 0) {
+        stream.metadata.latencyMs = (NSInteger)(_sessionLatency * 1000);
+    }
+
     // Check if we have received multiple frames for the same Stream-ID
     if (stream.receivedReply) {
         SPDY_WARNING(@"received duplicate SYN_REPLY");
@@ -722,7 +721,7 @@ - (void)didReadPingFrame:(SPDYPingFrame *)pingFrame frameDecoder:(SPDYFrameDecod
 
     if (pingId & 1) {
         if (pingId == 1) {
-            _sessionLatency = CFAbsoluteTimeGetCurrent() - _sessionPingOut;
+            _sessionLatency = _sessionPingStopwatch.elapsedSeconds;
             SPDY_DEBUG(@"received PING.%u response (%f)", pingId, _sessionLatency);
             _established = YES;
         }

SPDY/SPDYStopwatch.h

@@ -0,0 +1,20 @@
+//
+//  SPDYStopwatch.h
+//  SPDY
+//
+//  Copyright (c) 2014 Twitter, Inc. All rights reserved.
+//  Licensed under the Apache License v2.0
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Created by Kevin Goodier.
+//
+
+typedef double SPDYTimeInterval;
+
+@interface SPDYStopwatch : NSObject
++ (SPDYTimeInterval)currentSystemTime;
++ (SPDYTimeInterval)currentAbsoluteTime;
+- (id)init;
+- (void)reset;
+- (SPDYTimeInterval)elapsedSeconds;
+@end

SPDY/SPDYStopwatch.m

@@ -0,0 +1,67 @@
+//
+//  SPDYStopwatch.m
+//  SPDY
+//
+//  Copyright (c) 2014 Twitter, Inc. All rights reserved.
+//  Licensed under the Apache License v2.0
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Created by Kevin Goodier
+//
+
+#import <mach/mach_time.h>
+#import "SPDYStopwatch.h"
+
+@implementation SPDYStopwatch
+{
+    SPDYTimeInterval _startTime;
+}
+
+static dispatch_once_t __initTimebase;
+static double __machTimebaseToSeconds;
+static mach_timebase_info_data_t __machTimebase;
+
++ (void)initialize
+{
+    dispatch_once(&__initTimebase, ^{
+        kern_return_t status = mach_timebase_info(&__machTimebase);
+        // Everything will be 0 if this fails.
+        if (status != KERN_SUCCESS) {
+            __machTimebase.numer = 0;
+            __machTimebase.denom = 1;
+        }
+        __machTimebaseToSeconds = (double)__machTimebase.numer / ((double)__machTimebase.denom * 1000000000.0);
+    });
+}
+
++ (SPDYTimeInterval)currentSystemTime
+{
+    uint64_t now = mach_absolute_time();
+    return (SPDYTimeInterval)now * __machTimebaseToSeconds;
+}
+
++ (SPDYTimeInterval)currentAbsoluteTime
+{
+    return CFAbsoluteTimeGetCurrent();
+}
+
+- (id)init
+{
+    self = [super init];
+    if (self) {
+        _startTime = [SPDYStopwatch currentAbsoluteTime];
+    }
+    return self;
+}
+
+- (void)reset
+{
+    _startTime = [SPDYStopwatch currentAbsoluteTime];
+}
+
+- (SPDYTimeInterval)elapsedSeconds
+{
+    return [SPDYStopwatch currentAbsoluteTime] - _startTime;
+}
+
+@end