Fix thread-safety issues with BasePeripheral's computer list

There's a race condition here as attach/detach/getConnectedComputers may
be called from multiple threads. While we could switch to a CoW list,
it's probably nicer to use a ConcurrentHashMap like CC does.

Author: SquidDev

src/main/java/de/srendi/advancedperipherals/common/blocks/base/PeripheralBlockEntity.java

@@ -108,7 +108,7 @@ public void invalidateCaps() {
     @NotNull
     protected abstract T createPeripheral();
 
-    public List<IComputerAccess> getConnectedComputers() {
+    public Iterable<IComputerAccess> getConnectedComputers() {
         if (peripheral == null) // just avoid some NPE in strange cases
             return Collections.emptyList();
         return peripheral.getConnectedComputers();

src/main/java/de/srendi/advancedperipherals/lib/peripherals/BasePeripheral.java

@@ -15,12 +15,13 @@
 import org.jetbrains.annotations.Nullable;
 
 import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 
 public abstract class BasePeripheral<O extends IPeripheralOwner> implements IBasePeripheral<O>, IDynamicPeripheral {
 
-    protected final List<IComputerAccess> connectedComputers = new ArrayList<>();
+    protected final Set<IComputerAccess> connectedComputers = Collections.newSetFromMap(new ConcurrentHashMap<>());
     protected final String type;
     protected final O owner;
     protected final List<BoundMethod> pluggedMethods = new ArrayList<>();
@@ -63,7 +64,7 @@ protected void addPlugin(@NotNull IPeripheralPlugin plugin) {
     }
 
     @Override
-    public List<IComputerAccess> getConnectedComputers() {
+    public Iterable<IComputerAccess> getConnectedComputers() {
         return connectedComputers;
     }
 

src/main/java/de/srendi/advancedperipherals/lib/peripherals/IBasePeripheral.java

@@ -4,12 +4,10 @@
 import dan200.computercraft.api.peripheral.IPeripheral;
 import de.srendi.advancedperipherals.common.addons.computercraft.owner.IPeripheralOwner;
 
-import java.util.List;
-
 public interface IBasePeripheral<T extends IPeripheralOwner> extends IPeripheral {
     boolean isEnabled();
 
-    List<IComputerAccess> getConnectedComputers();
+    Iterable<IComputerAccess> getConnectedComputers();
 
     T getPeripheralOwner();
 }