/*
   * Copyright 2014 The Netty Project
   *
   * The Netty Project licenses this file to you under the Apache License,
   * version 2.0 (the "License"); you may not use this file except in compliance
   * with the License. You may obtain a copy of the License at:
   *
   *   https://www.apache.org/licenses/LICENSE-2.0
   *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  * License for the specific language governing permissions and limitations
  * under the License.
  */
  package io.netty.util.concurrent;
  
  import io.netty.util.internal.InternalThreadLocalMap;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.util.Arrays;
  import java.util.concurrent.atomic.AtomicReference;
  
  /**
   * A special {@link Thread} that provides fast access to {@link FastThreadLocal} variables.
   */
  public class FastThreadLocalThread extends Thread {
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(FastThreadLocalThread.class);
  
      /**
       * Sorted array of thread IDs that are treated like {@link FastThreadLocalThread}.
       */
      private static final AtomicReference<long[]> fallbackThreads = new AtomicReference<>(null);
  
      // This will be set to true if we have a chance to wrap the Runnable.
      private final boolean cleanupFastThreadLocals;
  
      private InternalThreadLocalMap threadLocalMap;
  
      public FastThreadLocalThread() {
          cleanupFastThreadLocals = false;
      }
  
      public FastThreadLocalThread(Runnable target) {
          super(FastThreadLocalRunnable.wrap(target));
          cleanupFastThreadLocals = true;
      }
  
      public FastThreadLocalThread(ThreadGroup group, Runnable target) {
          super(group, FastThreadLocalRunnable.wrap(target));
          cleanupFastThreadLocals = true;
      }
  
      public FastThreadLocalThread(String name) {
          super(name);
          cleanupFastThreadLocals = false;
      }
  
      public FastThreadLocalThread(ThreadGroup group, String name) {
          super(group, name);
          cleanupFastThreadLocals = false;
      }
  
      public FastThreadLocalThread(Runnable target, String name) {
          super(FastThreadLocalRunnable.wrap(target), name);
          cleanupFastThreadLocals = true;
      }
  
      public FastThreadLocalThread(ThreadGroup group, Runnable target, String name) {
          super(group, FastThreadLocalRunnable.wrap(target), name);
          cleanupFastThreadLocals = true;
      }
  
      public FastThreadLocalThread(ThreadGroup group, Runnable target, String name, long stackSize) {
          super(group, FastThreadLocalRunnable.wrap(target), name, stackSize);
          cleanupFastThreadLocals = true;
      }
  
      /**
       * Returns the internal data structure that keeps the thread-local variables bound to this thread.
       * Note that this method is for internal use only, and thus is subject to change at any time.
       */
      public final InternalThreadLocalMap threadLocalMap() {
          if (this != Thread.currentThread() && logger.isWarnEnabled()) {
              logger.warn(new RuntimeException("It's not thread-safe to get 'threadLocalMap' " +
                      "which doesn't belong to the caller thread"));
          }
          return threadLocalMap;
      }
  
      /**
       * Sets the internal data structure that keeps the thread-local variables bound to this thread.
       * Note that this method is for internal use only, and thus is subject to change at any time.
       */
      public final void setThreadLocalMap(InternalThreadLocalMap threadLocalMap) {
          if (this != Thread.currentThread() && logger.isWarnEnabled()) {
              logger.warn(new RuntimeException("It's not thread-safe to set 'threadLocalMap' " +
                     "which doesn't belong to the caller thread"));
         }
         this.threadLocalMap = threadLocalMap;
     }
 
     /**
      * Returns {@code true} if {@link FastThreadLocal#removeAll()} will be called once {@link #run()} completes.
      *
      * @deprecated Use {@link FastThreadLocalThread#currentThreadWillCleanupFastThreadLocals()} instead
      */
     @Deprecated
     public boolean willCleanupFastThreadLocals() {
         return cleanupFastThreadLocals;
     }
 
     /**
      * Returns {@code true} if {@link FastThreadLocal#removeAll()} will be called once {@link Thread#run()} completes.
      *
      * @deprecated Use {@link FastThreadLocalThread#currentThreadWillCleanupFastThreadLocals()} instead
      */
     @Deprecated
     public static boolean willCleanupFastThreadLocals(Thread thread) {
         return thread instanceof FastThreadLocalThread &&
                 ((FastThreadLocalThread) thread).willCleanupFastThreadLocals();
     }
 
     /**
      * Returns {@code true} if {@link FastThreadLocal#removeAll()} will be called once {@link Thread#run()} completes.
      */
     public static boolean currentThreadWillCleanupFastThreadLocals() {
         // intentionally doesn't accept a thread parameter to work with ScopedValue in the future
         Thread currentThread = currentThread();
         if (currentThread instanceof FastThreadLocalThread) {
             return ((FastThreadLocalThread) currentThread).willCleanupFastThreadLocals();
         }
         return isFastThreadLocalVirtualThread();
     }
 
     /**
      * Returns {@code true} if this thread supports {@link FastThreadLocal}.
      */
     public static boolean currentThreadHasFastThreadLocal() {
         // intentionally doesn't accept a thread parameter to work with ScopedValue in the future
         return currentThread() instanceof FastThreadLocalThread || isFastThreadLocalVirtualThread();
     }
 
     private static boolean isFastThreadLocalVirtualThread() {
         long[] arr = fallbackThreads.get();
         if (arr == null) {
             return false;
         }
         return Arrays.binarySearch(arr, Thread.currentThread().getId()) >= 0;
     }
 
     /**
      * Run the given task with {@link FastThreadLocal} support. This call should wrap the runnable for any thread that
      * is long-running enough to make treating it as a {@link FastThreadLocalThread} reasonable, but that can't
      * actually extend this class (e.g. because it's a virtual thread). Netty will use optimizations for recyclers and
      * allocators as if this was a {@link FastThreadLocalThread}.
      * <p>This method will clean up any {@link FastThreadLocal}s at the end, and
      * {@link #currentThreadWillCleanupFastThreadLocals()} will return {@code true}.
      * <p>At the moment, {@link FastThreadLocal} uses normal {@link ThreadLocal} as the backing storage here, but in
      * the future this may be replaced with scoped values, if semantics can be preserved and performance is good.
      *
      * @param runnable The task to run
      */
     public static void runWithFastThreadLocal(Runnable runnable) {
         Thread current = currentThread();
         if (current instanceof FastThreadLocalThread) {
             throw new IllegalStateException("Caller is a real FastThreadLocalThread");
         }
         long id = current.getId();
         fallbackThreads.updateAndGet(arr -> {
             if (arr == null) {
                 return new long[] { id };
             }
             int index = Arrays.binarySearch(arr, id);
             if (index >= 0) {
                 throw new IllegalStateException("Reentrant call to run()");
             }
             index = ~index; // same as -(index + 1)
             long[] next = new long[arr.length + 1];
             System.arraycopy(arr, 0, next, 0, index);
             next[index] = id;
             System.arraycopy(arr, index, next, index + 1, arr.length - index);
             return next;
         });
         try {
             runnable.run();
         } finally {
             fallbackThreads.getAndUpdate(arr -> {
                 if (arr == null || (arr.length == 1 && arr[0] == id)) {
                     return null;
                 }
                 int index = Arrays.binarySearch(arr, id);
                 if (index < 0) {
                     return arr;
                 }
                 long[] next = new long[arr.length - 1];
                 System.arraycopy(arr, 0, next, 0, index);
                 System.arraycopy(arr, index + 1, next, index, arr.length - index - 1);
                 return next;
             });
             FastThreadLocal.removeAll();
         }
     }
 
     /**
      * Query whether this thread is allowed to perform blocking calls or not.
      * {@link FastThreadLocalThread}s are often used in event-loops, where blocking calls are forbidden in order to
      * prevent event-loop stalls, so this method returns {@code false} by default.
      * <p>
      * Subclasses of {@link FastThreadLocalThread} can override this method if they are not meant to be used for
      * running event-loops.
      *
      * @return {@code false}, unless overriden by a subclass.
      */
     public boolean permitBlockingCalls() {
         return false;
     }
 }