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 *
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package org.jruby.cext;

import java.util.concurrent.locks.ReentrantLock;

/**
 * The {@link GIL} keeps locks for Threads running native code. Only one Thread can usually
 * be running C code at a time.
 */
final class GIL {

    private static final ReentrantLock lock = new ReentrantLock();

    private GIL() {
    }

    public static void acquire() {
        lock.lock();
    }

    /**
     * Acquire the lock n-times. This method is used to implement {@link JRuby#nativeBlockingRegion}.
     * After finishing execution of unmanaged code, the executing thread has to re-acquire all previously
     * owned locks (for cases where the execution of the Thread went through Java->C->Java->C multiple times)
     */
    public static void acquire(int lockCount) {
        for (int i = 0; i < lockCount; i++) {
            acquire();
        }
    }

    /**
     * Decrease the lock holding count by one, and do a {@link GC} run if this is
     * the last lock held by this thread.
     */
    public static void release() {
        try {
            if (lock.getHoldCount() == 1) {
                GC.cleanup();
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Fast unlocking without GC.
     */
    public static void releaseNoCleanup() {
        lock.unlock();
    }

    /**
     * Release all locks currently held by this thread.
     * @return the unlock count
     */
    public static int releaseAllLocks() {
        int count = lock.getHoldCount();
        for (int i = 0; i < count; i++) {
            lock.unlock();
        }
        return count;
    }
}
