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 * except in compliance with the License. You may obtain a copy of
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package org.jruby.runtime.opto;

import java.lang.invoke.SwitchPoint;
import java.util.List;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.concurrent.atomic.AtomicStampedReference;

public class FailoverSwitchPointInvalidator implements Invalidator {
    // a dummy switchpoint to use until we actually need a real one
    private static final SwitchPoint DUMMY = new SwitchPoint();
    static {SwitchPoint.invalidateAll(new SwitchPoint[]{DUMMY});}

    private final AtomicStampedReference<SwitchPoint> switchPoint = new AtomicStampedReference<>(DUMMY, 0);

    private final int maxFailures;
    
    public FailoverSwitchPointInvalidator(int maxFailures) {
        this.maxFailures = maxFailures;
    }
    
    public void invalidate() {
        SwitchPoint switchPoint = this.switchPoint.getReference();
        if (switchPoint == DUMMY) return;

        int failures = this.switchPoint.getStamp();
        SwitchPoint newSwitch = DUMMY;

        if (failures < maxFailures) {
            newSwitch = new SwitchPoint();
        }

        // Not important if we are successful, since update after read means another thread got to it first
        this.switchPoint.compareAndSet(switchPoint, newSwitch, failures, failures + 1);

        // Safe to invalidate now that we've updated
        SwitchPoint.invalidateAll(new SwitchPoint[]{switchPoint});
    }

    public void invalidateAll(List<Invalidator> invalidators) {
        SwitchPoint[] switchPoints = new SwitchPoint[invalidators.size()];
        
        for (int i = 0; i < invalidators.size(); i++) {
            Invalidator invalidator = invalidators.get(i);
            assert invalidator instanceof FailoverSwitchPointInvalidator;
            switchPoints[i] = ((FailoverSwitchPointInvalidator)invalidator).replaceSwitchPoint();
        }
        
        SwitchPoint.invalidateAll(switchPoints);
    }
    
    public synchronized Object getData() {
        while (true) {
            SwitchPoint switchPoint = this.switchPoint.getReference();
            int failures = this.switchPoint.getStamp();
            if (switchPoint == DUMMY && failures <= maxFailures) {
                SwitchPoint newSwitch = new SwitchPoint();
                if (this.switchPoint.compareAndSet(DUMMY, newSwitch, failures, failures)) {
                    return newSwitch;
                }
            } else {
                return switchPoint;
            }
        }
    }
    
    public synchronized SwitchPoint replaceSwitchPoint() {
        while (true) {
            SwitchPoint switchPoint = this.switchPoint.getReference();
            int failures = this.switchPoint.getStamp();
            if (switchPoint == DUMMY || failures > maxFailures) return DUMMY;
            SwitchPoint newSwitch = new SwitchPoint();
            if (this.switchPoint.compareAndSet(switchPoint, newSwitch, failures, failures + 1)) {
                return newSwitch;
            }
        }
    }
}