Introduce rtstella, replace mutex with spinlock in AudioQueue.

configure

@@ -320,6 +320,9 @@ case $_host in
 retron77)
 	_host_os=retron77
 	;;
+rtstella)
+	_host_os=rtstella
+	;;
 mingw32-cross)
 	_host_os=mingw32msvc
 	_host_cpu=i386
@@ -542,6 +545,10 @@ if test -n "$_host"; then
       _build_debugger=no
       _build_cheats=no
       _build_httplib=no
+      ;;
+		rtstella)
+			echo "Compiling rtstella"
+			DEFINES="$DEFINES -DRTSTELLA"
 			;;
 		mingw32-cross)
 			echo "Cross-compiling for Windows using MinGW."
@@ -834,6 +841,12 @@ case $_host_os in
 			MODULES="$MODULES $SRC_OS/unix"
 			INCLUDES="$INCLUDES -I$SRC_OS/unix"
 			;;
+		rtstella)
+			DEFINES="$DEFINES -DBSPF_UNIX"
+			MODULES="$MODULES $SRC_OS/unix $SRC_OS/rtstella"
+			INCLUDES="$INCLUDES -I$SRC_OS/unix -I$SRC_OS/rtstella"
+			LIBS="$LIBS -lpthread"
+			;;
 		darwin)
 			DEFINES="$DEFINES -DBSPF_UNIX -DMACOS_KEYS"
 			MODULES="$MODULES $SRC_OS/unix"

src/common/AudioQueue.cxx

@@ -54,7 +54,7 @@ uInt32 AudioQueue::capacity() const
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 uInt32 AudioQueue::size() const
 {
-  const lock_guard<mutex> guard(myMutex);
+  const lock_guard<Lock> guard(myLock);
 
   return mySize;
 }
@@ -74,7 +74,7 @@ uInt32 AudioQueue::fragmentSize() const
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Int16* AudioQueue::enqueue(Int16* fragment)
 {
-  const lock_guard<mutex> guard(myMutex);
+  const lock_guard<Lock> guard(myLock);
 
   Int16* newFragment = nullptr;
 
@@ -105,7 +105,7 @@ Int16* AudioQueue::enqueue(Int16* fragment)
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Int16* AudioQueue::dequeue(Int16* fragment)
 {
-  const lock_guard<mutex> guard(myMutex);
+  const lock_guard<Lock> guard(myLock);
 
   if (mySize == 0) return nullptr;
 
@@ -128,7 +128,7 @@ Int16* AudioQueue::dequeue(Int16* fragment)
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 void AudioQueue::closeSink(Int16* fragment)
 {
-  const lock_guard<mutex> guard(myMutex);
+  const lock_guard<Lock> guard(myLock);
 
   if (myFirstFragmentForDequeue && fragment)
     throw runtime_error("attempt to return unknown buffer on closeSink");

src/common/AudioQueue.hxx

@@ -23,6 +23,10 @@
 #include "bspf.hxx"
 #include "StaggeredLogger.hxx"
 
+#ifdef RTSTELLA
+#include "Spinlock.hxx"
+#endif
+
 /**
   This class implements an audio queue that acts both like a ring buffer
   and a pool of audio fragments. The TIA emulation core fills a fragment
@@ -36,6 +40,11 @@
 */
 class AudioQueue
 {
+  #ifdef RTSTELLA
+    using Lock = Spinlock;
+  #else
+    using Lock = std::Mutex;
+  #endif
   public:
 
     /**
@@ -120,7 +129,8 @@ class AudioQueue
     uInt32 myNextFragment{0};
 
     // We need a mutex for thread safety.
-    mutable std::mutex myMutex;
+    mutable Lock myLock;
+
 
     // The first (empty) enqueue call returns this fragment.
     Int16* myFirstFragmentForEnqueue{nullptr};

src/os/rtstella/Spinlock.cxx

@@ -0,0 +1,39 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2023 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#include "bspf.hxx"
+#include "Spinlock.hxx"
+
+Spinlock::Spinlock()
+{
+  pthread_spin_init(&mySpinlock, PTHREAD_PROCESS_PRIVATE);
+}
+
+Spinlock::~Spinlock()
+{
+  pthread_spin_destroy(&mySpinlock);
+}
+
+void Spinlock::lock()
+{
+  pthread_spin_lock(&mySpinlock);
+}
+
+void Spinlock::unlock()
+{
+  pthread_spin_unlock(&mySpinlock);
+}

src/os/rtstella/Spinlock.hxx

@@ -0,0 +1,39 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2023 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#include <pthread.h>
+
+#ifndef SPINLOCK_HXX
+#define SPINLOCK_HXX
+
+class Spinlock
+{
+  public:
+    Spinlock();
+
+    ~Spinlock();
+
+    void lock();
+
+    void unlock();
+
+  private:
+
+    pthread_spinlock_t mySpinlock;
+};
+
+#endif // SPINLOCK_HXX

src/os/rtstella/module.mk

@@ -0,0 +1,10 @@
+MODULE := src/os/rtstella
+
+MODULE_OBJS := \
+	src/os/rtstella/Spinlock.o
+
+MODULE_DIRS += \
+	src/os/rtstella
+
+# Include common rules
+include $(srcdir)/common.rules