Fix DelegateSemaphore synchronisation issues on Spigot (#1781)

* Fix DelegateSemaphore synchronisation issues on Spigot
 - Also effectively nullify it on paper - the synchronisation on the object is enough

* Remove unneeded imports

worldedit-bukkit/adapters/adapter-1_17_1/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/fawe/v1_17_R1_2/PaperweightGetBlocks.java

@@ -1,6 +1,7 @@
 package com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_17_R1_2;
 
 import com.fastasyncworldedit.bukkit.adapter.BukkitGetBlocks;
+import com.fastasyncworldedit.bukkit.adapter.DelegateSemaphore;
 import com.fastasyncworldedit.core.Fawe;
 import com.fastasyncworldedit.core.FaweCache;
 import com.fastasyncworldedit.core.configuration.Settings;
@@ -505,14 +506,16 @@ public class PaperweightGetBlocks extends CharGetBlocks implements BukkitGetBloc
                         }
 
                         //ensure that the server doesn't try to tick the chunksection while we're editing it (again).
-                        Semaphore lock = PaperweightPlatformAdapter.applyLock(existingSection);
                         PaperweightPlatformAdapter.clearCounts(existingSection);
                         if (PaperLib.isPaper()) {
                             existingSection.tickingList.clear();
                         }
+                        DelegateSemaphore lock = PaperweightPlatformAdapter.applyLock(existingSection);
 
+                        // Synchronize to prevent further acquisitions
                         synchronized (lock) {
-                            // lock.acquire();
+                            lock.acquire(); // Wait until we have the lock
+                            lock.release();
                             try {
                                 sectionLock.writeLock().lock();
                                 if (this.getChunk() != nmsChunk) {

worldedit-bukkit/adapters/adapter-1_17_1/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/fawe/v1_17_R1_2/PaperweightPlatformAdapter.java

@@ -169,9 +169,11 @@ public final class PaperweightPlatformAdapter extends NMSAdapter {
         return false;
     }
 
-    private static final ThreadLocal<Semaphore> SEMAPHORE_THREAD_LOCAL = ThreadLocal.withInitial(() -> new Semaphore(1));
+    // There is no point in having a functional semaphore for paper servers.
+    private static final ThreadLocal<DelegateSemaphore> SEMAPHORE_THREAD_LOCAL =
+            ThreadLocal.withInitial(() -> new DelegateSemaphore(1, null));
 
-    static Semaphore applyLock(LevelChunkSection section) {
+    static DelegateSemaphore applyLock(LevelChunkSection section) {
         if (PaperLib.isPaper()) {
             return SEMAPHORE_THREAD_LOCAL.get();
         }
@@ -180,8 +182,8 @@ public final class PaperweightPlatformAdapter extends NMSAdapter {
                 Unsafe unsafe = ReflectionUtils.getUnsafe();
                 PalettedContainer<net.minecraft.world.level.block.state.BlockState> blocks = section.getStates();
                 Semaphore currentLock = (Semaphore) unsafe.getObject(blocks, fieldLockOffset);
-                if (currentLock instanceof DelegateSemaphore) {
+                if (currentLock instanceof DelegateSemaphore delegateSemaphore) {
-                    return (DelegateSemaphore) currentLock;
+                    return delegateSemaphore;
                 }
                 DelegateSemaphore newLock = new DelegateSemaphore(1, currentLock);
                 unsafe.putObject(blocks, fieldLockOffset, newLock);

worldedit-bukkit/adapters/adapter-1_18/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/fawe/v1_18_R1/PaperweightGetBlocks.java

@@ -1,6 +1,7 @@
 package com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_18_R1;
 
 import com.fastasyncworldedit.bukkit.adapter.BukkitGetBlocks;
+import com.fastasyncworldedit.bukkit.adapter.DelegateSemaphore;
 import com.fastasyncworldedit.core.Fawe;
 import com.fastasyncworldedit.core.FaweCache;
 import com.fastasyncworldedit.core.configuration.Settings;
@@ -560,10 +561,12 @@ public class PaperweightGetBlocks extends CharGetBlocks implements BukkitGetBloc
                         if (PaperLib.isPaper()) {
                             existingSection.tickingList.clear();
                         }
-                        Semaphore lock = PaperweightPlatformAdapter.applyLock(existingSection);
+                        DelegateSemaphore lock = PaperweightPlatformAdapter.applyLock(existingSection);
 
+                        // Synchronize to prevent further acquisitions
                         synchronized (lock) {
-                            // lock.acquire();
+                            lock.acquire(); // Wait until we have the lock
+                            lock.release();
                             try {
                                 sectionLock.writeLock().lock();
                                 if (this.getChunk() != nmsChunk) {

worldedit-bukkit/adapters/adapter-1_18/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/fawe/v1_18_R1/PaperweightPlatformAdapter.java

@@ -190,9 +190,11 @@ public final class PaperweightPlatformAdapter extends NMSAdapter {
         return false;
     }
 
-    private static final ThreadLocal<Semaphore> SEMAPHORE_THREAD_LOCAL = ThreadLocal.withInitial(() -> new Semaphore(1));
+    // There is no point in having a functional semaphore for paper servers.
+    private static final ThreadLocal<DelegateSemaphore> SEMAPHORE_THREAD_LOCAL =
+            ThreadLocal.withInitial(() -> new DelegateSemaphore(1, null));
 
-    static Semaphore applyLock(LevelChunkSection section) {
+    static DelegateSemaphore applyLock(LevelChunkSection section) {
         if (PaperLib.isPaper()) {
             return SEMAPHORE_THREAD_LOCAL.get();
         }
@@ -204,8 +206,8 @@ public final class PaperweightPlatformAdapter extends NMSAdapter {
                         fieldThreadingDetectorOffset) ;
                 synchronized(currentThreadingDetector) {
                     Semaphore currentLock = (Semaphore) unsafe.getObject(currentThreadingDetector, fieldLockOffset);
-                    if (currentLock instanceof DelegateSemaphore) {
+                    if (currentLock instanceof DelegateSemaphore delegateSemaphore) {
-                        return (DelegateSemaphore) currentLock;
+                        return delegateSemaphore;
                     }
                     DelegateSemaphore newLock = new DelegateSemaphore(1, currentLock);
                     unsafe.putObject(currentThreadingDetector, fieldLockOffset, newLock);

worldedit-bukkit/adapters/adapter-1_18_2/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/fawe/v1_18_R2/PaperweightGetBlocks.java

@@ -1,6 +1,7 @@
 package com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_18_R2;
 
 import com.fastasyncworldedit.bukkit.adapter.BukkitGetBlocks;
+import com.fastasyncworldedit.bukkit.adapter.DelegateSemaphore;
 import com.fastasyncworldedit.core.Fawe;
 import com.fastasyncworldedit.core.FaweCache;
 import com.fastasyncworldedit.core.configuration.Settings;
@@ -576,10 +577,12 @@ public class PaperweightGetBlocks extends CharGetBlocks implements BukkitGetBloc
                         if (PaperLib.isPaper()) {
                             existingSection.tickingList.clear();
                         }
-                        Semaphore lock = PaperweightPlatformAdapter.applyLock(existingSection);
+                        DelegateSemaphore lock = PaperweightPlatformAdapter.applyLock(existingSection);
 
+                        // Synchronize to prevent further acquisitions
                         synchronized (lock) {
-                            // lock.acquire();
+                            lock.acquire(); // Wait until we have the lock
+                            lock.release();
                             try {
                                 sectionLock.writeLock().lock();
                                 if (this.getChunk() != nmsChunk) {

worldedit-bukkit/adapters/adapter-1_18_2/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/fawe/v1_18_R2/PaperweightPlatformAdapter.java

@@ -189,9 +189,11 @@ public final class PaperweightPlatformAdapter extends NMSAdapter {
         return false;
     }
 
-    private static final ThreadLocal<Semaphore> SEMAPHORE_THREAD_LOCAL = ThreadLocal.withInitial(() -> new Semaphore(1));
+    // There is no point in having a functional semaphore for paper servers.
+    private static final ThreadLocal<DelegateSemaphore> SEMAPHORE_THREAD_LOCAL =
+            ThreadLocal.withInitial(() -> new DelegateSemaphore(1, null));
 
-    static Semaphore applyLock(LevelChunkSection section) {
+    static DelegateSemaphore applyLock(LevelChunkSection section) {
         if (PaperLib.isPaper()) {
             return SEMAPHORE_THREAD_LOCAL.get();
         }
@@ -205,8 +207,8 @@ public final class PaperweightPlatformAdapter extends NMSAdapter {
                 );
                 synchronized (currentThreadingDetector) {
                     Semaphore currentLock = (Semaphore) unsafe.getObject(currentThreadingDetector, fieldLockOffset);
-                    if (currentLock instanceof DelegateSemaphore) {
+                    if (currentLock instanceof DelegateSemaphore delegateSemaphore) {
-                        return currentLock;
+                        return delegateSemaphore;
                     }
                     DelegateSemaphore newLock = new DelegateSemaphore(1, currentLock);
                     unsafe.putObject(currentThreadingDetector, fieldLockOffset, newLock);

worldedit-bukkit/src/main/java/com/fastasyncworldedit/bukkit/adapter/DelegateSemaphore.java

@@ -14,6 +14,9 @@ public class DelegateSemaphore extends Semaphore {
     // this is bad
     @Override
     public synchronized boolean tryAcquire() {
+        if (delegate == null) {
+            return true;
+        }
         try {
             this.delegate.acquire();
             return true;
@@ -24,11 +27,17 @@ public class DelegateSemaphore extends Semaphore {
 
     @Override
     public synchronized void acquire() throws InterruptedException {
+        if (delegate == null) {
+            return;
+        }
         this.delegate.acquire();
     }
 
     @Override
-    public synchronized void release() {
+    public void release() {
+        if (delegate == null) {
+            return;
+        }
         this.delegate.release();
     }