Master Sync: preallocate buffers in engine thread func.

pickMaster gets called from the engine thread so we have to be careful to
avoid memory allocation.  Preallocating a constant number fixes this.

Also make kMaxNumberOfDecks a proper mixxx-global value, and check against
it when we add decks.  If someone one day invents a skin that uses 6 or 8
decks, this warning will get tripped (but shouldn't break anything
fundamental in Mixxx).

4 files changed, 14 insertions, 5 deletions

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index 18c22be226..8b18a0a261 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -24,6 +24,7 @@
 #include "engine/channels/enginechannel.h"
 #include "engine/sync/internalclock.h"
 #include "util/assert.h"
+#include "util/defs.h"
 
 const bool SYNC_DEBUG = false;
 
@@ -38,6 +39,9 @@ Syncable* EngineSync::pickMaster(Syncable* enabling_syncable) {
     std::vector<Syncable*> stopped_sync_decks;
     std::vector<Syncable*> playing_sync_decks;
 
+    stopped_sync_decks.reserve(kMaxNumberOfDecks);
+    playing_sync_decks.reserve(kMaxNumberOfDecks);
+
     if (enabling_syncable != nullptr && enabling_syncable->getBaseBpm() != 0.0) {
         if (enabling_syncable->isPlaying()) {
             playing_sync_decks.push_back(enabling_syncable);
diff --git a/src/mixer/playermanager.cpp b/src/mixer/playermanager.cpp
index 5240f71210..d377a9538a 100644
--- a/src/mixer/playermanager.cpp
+++ b/src/mixer/playermanager.cpp
@@ -20,6 +20,7 @@
 #include "soundio/soundmanager.h"
 #include "track/track.h"
 #include "util/assert.h"
+#include "util/defs.h"
 #include "util/logger.h"
 #include "util/stat.h"
 #include "util/sleepableqthread.h"
@@ -268,6 +269,12 @@ void PlayerManager::slotChangeNumDecks(double v) {
     QMutexLocker locker(&m_mutex);
     int num = (int)v;
 
+    VERIFY_OR_DEBUG_ASSERT(num <= kMaxNumberOfDecks) {
+        qWarning() << "Number of decks exceeds the maximum we expect."
+                   << num << "vs" << kMaxNumberOfDecks
+                   << " Please update util/defs.h";
+    }
+
     // Update the soundmanager config even if the number of decks has been
     // reduced.
     m_pSoundManager->setConfiguredDeckCount(num);
diff --git a/src/util/defs.h b/src/util/defs.h
index 0b151a6260..f34bf34f99 100644
--- a/src/util/defs.h
+++ b/src/util/defs.h
@@ -5,4 +5,6 @@
 //TODO: Replace this with mixxx::AudioParameters::bufferSize()
 const unsigned int MAX_BUFFER_LEN = 160000;
 
+const int kMaxNumberOfDecks = 4;
+
 #endif /* DEFS_H */
diff --git a/src/vinylcontrol/vinylcontrolmanager.h b/src/vinylcontrol/vinylcontrolmanager.h
index 6002330499..4bf975331b 100644
--- a/src/vinylcontrol/vinylcontrolmanager.h
+++ b/src/vinylcontrol/vinylcontrolmanager.h
@@ -15,6 +15,7 @@
 #include "soundio/soundmanagerutil.h"
 #include "preferences/usersettings.h"
 #include "vinylcontrol/vinylsignalquality.h"
+#include "util/defs.h"
 
 class ControlProxy;
 class ControlPushButton;
@@ -23,11 +24,6 @@ class VinylControl;
 class VinylControlProcessor;
 
 
-const int kMaxNumberOfDecks = 4; // set to 4 because it will ideally not be more
-// or less than the number of vinyl-controlled decks but will probably be
-// forgotten in any 2->4 deck switchover. Only real consequence is
-// sizeof(void*)*2 bytes of wasted memory if we're only using 2 decks -bkgood
-
 // VinylControlManager is the main-thread interface that other parts of Mixxx
 // use to interact with the vinyl control subsystem (other than controls exposed
 // by vinyl control to the rest of Mixxx). VinylControlManager starts a