From 66eeff040b57bc7dd89bdd08f94eec49c9c7ebf1 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Sun, 7 Jun 2020 10:46:24 +0700
Subject: [PATCH] reduce calls to time.Now() from the flow controller

---
 internal/flowcontrol/base_flow_controller.go       | 11 ++++++-----
 internal/flowcontrol/base_flow_controller_test.go  |  2 +-
 internal/flowcontrol/connection_flow_controller.go |  3 ++-
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/internal/flowcontrol/base_flow_controller.go b/internal/flowcontrol/base_flow_controller.go
index 6a0aa3c5..d11e05f4 100644
--- a/internal/flowcontrol/base_flow_controller.go
+++ b/internal/flowcontrol/base_flow_controller.go
@@ -68,7 +68,7 @@ func (c *baseFlowController) AddBytesRead(n protocol.ByteCount) {
 	// pretend we sent a WindowUpdate when reading the first byte
 	// this way auto-tuning of the window size already works for the first WindowUpdate
 	if c.bytesRead == 0 {
-		c.startNewAutoTuningEpoch()
+		c.startNewAutoTuningEpoch(time.Now())
 	}
 	c.bytesRead += n
 }
@@ -105,15 +105,16 @@ func (c *baseFlowController) maybeAdjustWindowSize() {
 	}
 
 	fraction := float64(bytesReadInEpoch) / float64(c.receiveWindowSize)
-	if time.Since(c.epochStartTime) < time.Duration(4*fraction*float64(rtt)) {
+	now := time.Now()
+	if now.Sub(c.epochStartTime) < time.Duration(4*fraction*float64(rtt)) {
 		// window is consumed too fast, try to increase the window size
 		c.receiveWindowSize = utils.MinByteCount(2*c.receiveWindowSize, c.maxReceiveWindowSize)
 	}
-	c.startNewAutoTuningEpoch()
+	c.startNewAutoTuningEpoch(now)
 }
 
-func (c *baseFlowController) startNewAutoTuningEpoch() {
-	c.epochStartTime = time.Now()
+func (c *baseFlowController) startNewAutoTuningEpoch(now time.Time) {
+	c.epochStartTime = now
 	c.epochStartOffset = c.bytesRead
 }
 
diff --git a/internal/flowcontrol/base_flow_controller_test.go b/internal/flowcontrol/base_flow_controller_test.go
index 741caae5..273b9a2b 100644
--- a/internal/flowcontrol/base_flow_controller_test.go
+++ b/internal/flowcontrol/base_flow_controller_test.go
@@ -145,7 +145,7 @@ var _ = Describe("Base Flow controller", func() {
 
 			It("doesn't increase the window size when no RTT estimate is available", func() {
 				setRtt(0)
-				controller.startNewAutoTuningEpoch()
+				controller.startNewAutoTuningEpoch(time.Now())
 				controller.AddBytesRead(400)
 				offset := controller.getWindowUpdate()
 				Expect(offset).ToNot(BeZero()) // make sure a window update is sent
diff --git a/internal/flowcontrol/connection_flow_controller.go b/internal/flowcontrol/connection_flow_controller.go
index 8b9d51ec..19de1c77 100644
--- a/internal/flowcontrol/connection_flow_controller.go
+++ b/internal/flowcontrol/connection_flow_controller.go
@@ -2,6 +2,7 @@ package flowcontrol
 
 import (
 	"fmt"
+	"time"
 
 	"github.com/lucas-clemente/quic-go/internal/congestion"
 	"github.com/lucas-clemente/quic-go/internal/protocol"
@@ -86,7 +87,7 @@ func (c *connectionFlowController) EnsureMinimumWindowSize(inc protocol.ByteCoun
 	if inc > c.receiveWindowSize {
 		c.logger.Debugf("Increasing receive flow control window for the connection to %d kB, in response to stream flow control window increase", c.receiveWindowSize/(1<<10))
 		c.receiveWindowSize = utils.MinByteCount(inc, c.maxReceiveWindowSize)
-		c.startNewAutoTuningEpoch()
+		c.startNewAutoTuningEpoch(time.Now())
 	}
 	c.mutex.Unlock()
 }