Refactor use of strings in the engine. 10-20% callback speed improvement.

* Add ChannelHandle, a wrapper class for an integer handle that starts
  at 0 and increments.
* Add ChannelHandleFactory for assigning integer handles to group
  strings.
* Add ChannelHandleMap, an associative container mapping ChannelHandle
  to a template data type T. Backed by a QVarLengthArray with a
  pre-allocation of 256. Supports fast O(1) lookups (simple memory
  indexing) and amortized O(1) inserts.
* Re-factor engine and effects code to use ChannelHandle.
* Update EffectProcessor to use ChannelHandleMap instead of QHash.
* Update EngineEffectChain to use ChannelHandleMap instead of QLinkedList.

I did two tests -- one with effects inactive and one with effects
active. I measured total-callback processing time improvements of 20%
(1 track, no effects) and 13% (2 tracks, effects enabled). From this I
conclude that the QHash and QLinkedList introduced tons of wasted
cycles (which agrees with my profiling results from a month or two
ago).

Test 1:
* No effects active
* optimize=portable
* single track playing for 1 minute
* began sampling 20 seconds in to get rid of the load-track jitters

Base:
Debug [Main]: Stat("SoundDevicePortAudio::callbackProcess prepare 1, Built-in Output","count=45014,sum=3.82151e+09ns,average=84896ns,min=26393ns,max=429257ns,variance=9.41766e+08ns^2,stddev=30688.2ns")

Experiment:
Debug [Main]: Stat("SoundDevicePortAudio::callbackProcess prepare 1, Built-in Output","count=44856,sum=3.02069e+09ns,average=67342ns,min=20400ns,max=323169ns,variance=5.93287e+08ns^2,stddev=24357.5ns")

Results:
Minimum: reduced by 22.7%
Maximum: reduced by 24.7%
Average: reduced by 20.7%
StdDev: reduced by 20.6%

Test 2:
* One effect active on [Master].
* One effect active on [Channel1]
* optimize=portable
* two tracks playing for 1 minute
* began sampling 20 seconds in to get rid of the load-track jitters

Base:
Debug [Main]: Stat("SoundDevicePortAudio::callbackProcess prepare 1, Built-in Output","count=44937,sum=4.76277e+09ns,average=105988ns,min=38434ns,max=326061ns,variance=1.49815e+09ns^2,stddev=38706ns")

Experiment:
Debug [Main]: Stat("SoundDevicePortAudio::callbackProcess prepare 1, Built-in Output","count=45191,sum=4.15799e+09ns,average=92009.3ns,min=31693ns,max=333664ns,variance=1.11131e+09ns^2,stddev=33336.3ns")

Results:
Minimum: reduced by 17.5%
Maximum: increase by 0.02%
Average: reduced by 13.2%
StdDev: reduced by 13.9%

1 files changed, 7 insertions, 6 deletions

diff --git a/src/effects/effectchain.h b/src/effects/effectchain.h
index 30e16da50d..594eafdb36 100644
--- a/src/effects/effectchain.h
+++ b/src/effects/effectchain.h
@@ -8,6 +8,7 @@
 
 #include "util.h"
 #include "effects/effect.h"
+#include "engine/channelhandle.h"
 
 class EffectsManager;
 class EngineEffectRack;
@@ -37,10 +38,10 @@ class EffectChain : public QObject {
     void setEnabled(bool enabled);
 
     // Activates EffectChain processing for the provided group.
-    void enableForGroup(const QString& group);
-    bool enabledForGroup(const QString& group) const;
-    const QSet<QString>& enabledGroups() const;
-    void disableForGroup(const QString& group);
+    void enableForChannel(const ChannelHandleAndGroup& group);
+    bool enabledForChannel(const ChannelHandleAndGroup& group) const;
+    const QSet<ChannelHandleAndGroup>& enabledChannels() const;
+    void disableForChannel(const ChannelHandleAndGroup& group);
 
     EffectChainPointer prototype() const;
 
@@ -105,7 +106,7 @@ class EffectChain : public QObject {
     void enabledChanged(bool enabled);
     void mixChanged(double v);
     void insertionTypeChanged(EffectChain::InsertionType type);
-    void groupStatusChanged(const QString& group, bool enabled);
+    void channelStatusChanged(const QString& group, bool enabled);
 
   private:
     QString debugString() const {
@@ -124,7 +125,7 @@ class EffectChain : public QObject {
     InsertionType m_insertionType;
     double m_dMix;
 
-    QSet<QString> m_enabledGroups;
+    QSet<ChannelHandleAndGroup> m_enabledChannels;
     QList<EffectPointer> m_effects;
     EngineEffectChain* m_pEngineEffectChain;
     bool m_bAddedToEngine;