Add support for running multiple computers at the same time

- ComputerThread constructs multiple threads instead of just one,
   depending on a config options.
 - The synchronized blocks of PeripheralAPI.PeripheralWrapper have been
   shifted a little to ensure no deadlocks occur.

src/main/java/dan200/computercraft/ComputerCraft.java

@@ -127,6 +127,7 @@ public class ComputerCraft
     public static boolean disable_lua51_features = false;
     public static String default_computer_settings = "";
     public static boolean debug_enable = false;
+    public static int computer_threads = 1;
     public static boolean logPeripheralErrors = false;
 
     public static boolean enableCommandBlock = false;
@@ -208,6 +209,7 @@ public class ComputerCraft
         public static Property disable_lua51_features;
         public static Property default_computer_settings;
         public static Property debug_enable;
+        public static Property computer_threads;
         public static Property logPeripheralErrors;
 
         public static Property enableCommandBlock;
@@ -308,6 +310,13 @@ public class ComputerCraft
         Config.debug_enable = Config.config.get( Configuration.CATEGORY_GENERAL, "debug_enable", debug_enable );
         Config.debug_enable.setComment( "Enable Lua's debug library. Whilst this should be safe for general use, it may allow players to interact with other computers. Enable at your own risk." );
 
+        Config.computer_threads = Config.config.get( Configuration.CATEGORY_GENERAL, "computer_threads", computer_threads );
+        Config.computer_threads
+            .setMinValue( 1 )
+            .setRequiresWorldRestart( true )
+            .setComment( "Set the number of threads computers can run on. A higher number means more computers can run at once, but may induce lag.\n" +
+                "Please note that some mods may not work with a thread count higher than 1. Use with caution." );
+
         Config.logPeripheralErrors = Config.config.get( Configuration.CATEGORY_GENERAL, "logPeripheralErrors", logPeripheralErrors );
         Config.logPeripheralErrors.setComment( "Log exceptions thrown by peripherals and other Lua objects.\n" +
             "This makes it easier for mod authors to debug problems, but may result in log spam should people use buggy methods." );
@@ -378,6 +387,7 @@ public class ComputerCraft
         disable_lua51_features = Config.disable_lua51_features.getBoolean();
         default_computer_settings = Config.default_computer_settings.getString();
         debug_enable = Config.debug_enable.getBoolean();
+        computer_threads = Config.computer_threads.getInt();
         logPeripheralErrors = Config.logPeripheralErrors.getBoolean();
 
         enableCommandBlock = Config.enableCommandBlock.getBoolean();

src/main/java/dan200/computercraft/core/apis/PeripheralAPI.java

@@ -84,12 +84,14 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
             m_peripheral.attach( this );
         }
 
-        public synchronized void detach()
+        public void detach()
         {
             // Call detach
             m_peripheral.detach( this );
-            m_attached = false;
 
+            synchronized( this )
+            {
+                m_attached = false;
                 // Unmount everything the detach function forgot to do
                 for( String m_mount : m_mounts )
                 {
@@ -97,6 +99,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
                 }
                 m_mounts.clear();
             }
+        }
 
         public Object[] call( ILuaContext context, String methodName, Object[] arguments ) throws LuaException, InterruptedException
         {
@@ -209,7 +212,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
         }
 
         @Override
-        public synchronized int getID()
+        public int getID()
         {
             if( !m_attached ) {
                 throw new RuntimeException( "You are not attached to this Computer" );
@@ -218,7 +221,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
         }
 
         @Override
-        public synchronized void queueEvent( @Nonnull final String event, final Object[] arguments )
+        public void queueEvent( @Nonnull final String event, final Object[] arguments )
         {
             if( !m_attached ) {
                 throw new RuntimeException( "You are not attached to this Computer" );
@@ -228,7 +231,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
 
         @Nonnull
         @Override
-        public synchronized String getAttachmentName()
+        public String getAttachmentName()
         {
             if( !m_attached ) {
                 throw new RuntimeException( "You are not attached to this Computer" );
@@ -464,7 +467,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
                 // call
                 int side = parseSide( args );
                 String methodName = getString( args, 1 );
-                Object[] methodArgs = trimArray( args, 2 );
+                Object[] methodArgs = Arrays.copyOfRange( args, 2, args.length );
 
                 if( side >= 0 )
                 {
@@ -489,11 +492,6 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
 
     // Privates
 
-    private Object[] trimArray( Object[] array, int skip )
-    {
-        return Arrays.copyOfRange( array, skip, array.length );
-    }
-
     private int parseSide( Object[] args ) throws LuaException
     {
         String side = getString( args, 0 );

src/main/java/dan200/computercraft/core/computer/ComputerThread.java

@@ -53,9 +53,10 @@ public class ComputerThread
     /**
      * The thread tasks execute on
      */
-    private static Thread s_thread = null;
+    private static Thread[] s_threads = null;
 
-    private static final AtomicInteger s_counter = new AtomicInteger( 1 );
+    private static final AtomicInteger s_ManagerCounter = new AtomicInteger( 1 );
+    private static final AtomicInteger s_DelegateCounter = new AtomicInteger( 1 );
 
     /**
      * Start the computer thread
@@ -65,17 +66,25 @@ public class ComputerThread
         synchronized( s_stateLock )
         {
             s_stopped = false;
-            if( s_thread == null || !s_thread.isAlive() )
+            if( s_threads == null || s_threads.length != ComputerCraft.computer_threads )
             {
+                s_threads = new Thread[ ComputerCraft.computer_threads ];
+            }
+
             SecurityManager manager = System.getSecurityManager();
             final ThreadGroup group = manager == null ? Thread.currentThread().getThreadGroup() : manager.getThreadGroup();
-
+            for( int i = 0; i < s_threads.length; i++ )
-                Thread thread = s_thread = new Thread( group, new TaskExecutor(), "ComputerCraft-Computer-Manager" );
+            {
+                Thread thread = s_threads[ i ];
+                if( thread == null || !thread.isAlive() )
+                {
+                    thread = s_threads[ i ] = new Thread( group, new TaskExecutor(), "ComputerCraft-Computer-Manager-" + s_ManagerCounter.getAndIncrement() );
                     thread.setDaemon( true );
                     thread.start();
                 }
             }
         }
+    }
 
     /**
      * Attempt to stop the computer thread
@@ -84,12 +93,15 @@ public class ComputerThread
     {
         synchronized( s_stateLock )
         {
-            if( s_thread != null )
+            if( s_threads != null )
             {
                 s_stopped = true;
-                if( s_thread.isAlive() )
+                for( Thread thread : s_threads )
                 {
-                    s_thread.interrupt();
+                    if( thread != null && thread.isAlive() )
+                    {
+                        thread.interrupt();
+                    }
                 }
             }
         }
@@ -178,7 +190,7 @@ public class ComputerThread
 
                 SecurityManager manager = System.getSecurityManager();
                 final ThreadGroup group = manager == null ? Thread.currentThread().getThreadGroup() : manager.getThreadGroup();
-                Thread thread = this.thread = new Thread( group, runner, "ComputerCraft-Computer-Runner" + s_counter.getAndIncrement() );
+                Thread thread = this.thread = new Thread( group, runner, "ComputerCraft-Computer-Runner" + s_DelegateCounter.getAndIncrement() );
                 thread.setDaemon( true );
                 thread.start();
             }