thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.circuitbreaker;


import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import dk.thoerup.circuitbreaker.notification.Notifier;
import dk.thoerup.circuitbreaker.notification.NullNotifier;

/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
 * 
 *  example of how it can be used

 private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
                class TestInvocation implements CircuitInvocation {
                        String url;
                        public TestInvocation(String url) {
                                this.url = url;
                        }
                        public Object proceed() throws Exception{
                                
                                URL u = new URL(url);
                                URLConnection c = u.openConnection();
                                c.connect();
                                InputStream in = c.getInputStream();
                                in.close();
                                                        
                                
                                return "hello";
                        }
                        
                }
                try {
                        String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
                        response.getWriter().print(s);
                } catch (Exception e) {
                        logger.warning( e.getMessage() );
                        response.sendError(500);
                        return;
                }
                
        }
 */


public class CircuitBreaker{
        
        private volatile CircuitBreakerState currentState;
        
        private final OpenState open = new OpenState();
        private final HalfOpenState halfOpen = new HalfOpenState();
        private final ClosedState closed = new ClosedState();
        
        private String name;
        
        private ExecutorService executor = null;        
        private Notifier notifier = new NullNotifier();
        
        public CircuitBreaker(String name, int threshold, long timeoutMS) {
                closed.setThreshold(threshold);
                open.setTimeout(timeoutMS);
                
                this.name = name;
        
                //set correct intial state
                internalReset();
        }
        
        public synchronized void shutdown() {
                if (executor != null) {
                        executor.shutdown();
                }
        }
        
        
    public Object invoke(CircuitInvocation invocation) throws Exception
    {
        Object result = null;
        try
        {
            getState().preInvoke(this);
            result = invocation.proceed();
            getState().postInvoke(this);
        }
        catch(Exception e)
        {
            getState().onError(this, e);
            throw e;
        }
        return result;
    }
    
    public void tripBreaker() {
        commonTripBreaker(Notifier.Event.BreakerTripped);
    }
    
        //a re-trip should basically do the same as a normal trip, but it is here just to differentiate the two different events
    public void retripBreaker() {
        commonTripBreaker(Notifier.Event.BreakerRetripped);
    }
    
    private void commonTripBreaker(Notifier.Event event) {
        synchronized(this) {
                if (currentState != open) { // TODO:Is this conditional necessary ??
                        open.trip();
                        currentState = open;
                
                        notifier.sendNotification(name, event);
                }
        }       
    }

    public void attemptReset() {
        synchronized(this) {
                if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
                        currentState = halfOpen;
                        notifier.sendNotification(name, Notifier.Event.BreakerAttemptReset);
                }
        }
        
    }
    
    public void reset() {
        synchronized(this) {
                if (currentState != closed) { // TODO: Is this conditional necessary ??
                        internalReset();
                        notifier.sendNotification(name, Notifier.Event.BreakerReset);
                }
        }
    }
    
    //This one actually sets the correct closed/reset state 
    private void internalReset() {
                closed.resetFailureCount();
                currentState = closed;          
    }
    
    
    private CircuitBreakerState getState() {
        synchronized(this) {
                return currentState;
        }
    }
    
    public boolean isClosed() {
        return (getState() == closed); 
    }
    
    public boolean isOpen() {
        return (getState() == open); 
    }
    
    public String getName() {
        return name;
    }
    
    public String getStateName() {
        return getState().getName();
    }
    
    public int getThreshold() {
        return closed.getThreshold();
    }
    
    public int getTimeout() {
        return (int)open.getTimeout();
    }
    
    public int getFailureCount() {
        if (getState() == closed) {
                return closed.getFailureCount();
        } else {
                return -1;
        }
    }
    
    public long getElapsed() {
        if (getState() == open) {
                return open.getElapsed();
        } else {
                return -1;
        }
    }
    
    public void setNotifier(Notifier notifier) {
        this.notifier = notifier;
    }
    
    public String getNotifierName() {
        return notifier.getClass().getName();
    }
    
    public synchronized ExecutorService getExecutor() {
        
        if (executor == null) {
                executor = Executors.newFixedThreadPool(1);
        }
        
        return executor;
        
    }
 
}
1	torben	467	package dk.thoerup.circuitbreaker;
2	torben	393
3
4	torben	1148	import java.util.concurrent.ExecutorService;
5			import java.util.concurrent.Executors;
6
7	torben	467	import dk.thoerup.circuitbreaker.notification.Notifier;
8			import dk.thoerup.circuitbreaker.notification.NullNotifier;
9	torben	409
10	torben	394	/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
11			*
12			* example of how it can be used
13	torben	395
14			private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
15			protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
16	torben	393	class TestInvocation implements CircuitInvocation {
17			String url;
18			public TestInvocation(String url) {
19			this.url = url;
20			}
21			public Object proceed() throws Exception{
22
23			URL u = new URL(url);
24			URLConnection c = u.openConnection();
25			c.connect();
26			InputStream in = c.getInputStream();
27			in.close();
28
29
30			return "hello";
31			}
32
33			}
34			try {
35			String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
36			response.getWriter().print(s);
37	torben	452	} catch (Exception e) {
38	torben	393	logger.warning( e.getMessage() );
39			response.sendError(500);
40			return;
41			}
42
43			}
44			*/
45
46
47			public class CircuitBreaker{
48
49	torben	443	private volatile CircuitBreakerState currentState;
50	torben	393
51	torben	424	private final OpenState open = new OpenState();
52			private final HalfOpenState halfOpen = new HalfOpenState();
53			private final ClosedState closed = new ClosedState();
54	torben	393
55			private String name;
56
57	torben	1148	private ExecutorService executor = null;
58	torben	409	private Notifier notifier = new NullNotifier();
59
60	torben	393	public CircuitBreaker(String name, int threshold, long timeoutMS) {
61			closed.setThreshold(threshold);
62			open.setTimeout(timeoutMS);
63
64			this.name = name;
65	torben	625
66	torben	627	//set correct intial state
67			internalReset();
68	torben	393	}
69
70	torben	1148	public synchronized void shutdown() {
71			if (executor != null) {
72			executor.shutdown();
73			}
74			}
75	torben	393
76	torben	1148
77	torben	450	public Object invoke(CircuitInvocation invocation) throws Exception
78	torben	393	{
79			Object result = null;
80			try
81			{
82			getState().preInvoke(this);
83			result = invocation.proceed();
84			getState().postInvoke(this);
85			}
86	torben	450	catch(Exception e)
87	torben	393	{
88	torben	450	getState().onError(this, e);
89			throw e;
90	torben	393	}
91			return result;
92			}
93
94			public void tripBreaker() {
95	torben	871	commonTripBreaker(Notifier.Event.BreakerTripped);
96	torben	393	}
97
98	torben	864	//a re-trip should basically do the same as a normal trip, but it is here just to differentiate the two different events
99			public void retripBreaker() {
100	torben	871	commonTripBreaker(Notifier.Event.BreakerRetripped);
101			}
102
103			private void commonTripBreaker(Notifier.Event event) {
104			synchronized(this) {
105	torben	864	if (currentState != open) { // TODO:Is this conditional necessary ??
106			open.trip();
107			currentState = open;
108
109	torben	871	notifier.sendNotification(name, event);
110	torben	864	}
111	torben	871	}
112	torben	864	}
113
114	torben	393	public void attemptReset() {
115			synchronized(this) {
116	torben	426	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
117			currentState = halfOpen;
118			notifier.sendNotification(name, Notifier.Event.BreakerAttemptReset);
119			}
120	torben	393	}
121	torben	409
122	torben	393	}
123
124			public void reset() {
125			synchronized(this) {
126	torben	426	if (currentState != closed) { // TODO: Is this conditional necessary ??
127	torben	627	internalReset();
128	torben	426	notifier.sendNotification(name, Notifier.Event.BreakerReset);
129			}
130	torben	393	}
131			}
132
133	torben	627	//This one actually sets the correct closed/reset state
134			private void internalReset() {
135			closed.resetFailureCount();
136			currentState = closed;
137			}
138	torben	397
139	torben	627
140	torben	393	private CircuitBreakerState getState() {
141			synchronized(this) {
142			return currentState;
143			}
144			}
145	torben	397
146	torben	447	public boolean isClosed() {
147			return (getState() == closed);
148			}
149
150			public boolean isOpen() {
151			return (getState() == open);
152			}
153
154	torben	397	public String getName() {
155			return name;
156			}
157
158			public String getStateName() {
159			return getState().getName();
160			}
161
162			public int getThreshold() {
163			return closed.getThreshold();
164			}
165
166	torben	413	public int getTimeout() {
167			return (int)open.getTimeout();
168			}
169
170	torben	397	public int getFailureCount() {
171			if (getState() == closed) {
172			return closed.getFailureCount();
173			} else {
174			return -1;
175			}
176			}
177
178			public long getElapsed() {
179			if (getState() == open) {
180			return open.getElapsed();
181			} else {
182			return -1;
183			}
184			}
185	torben	409
186			public void setNotifier(Notifier notifier) {
187			this.notifier = notifier;
188			}
189
190			public String getNotifierName() {
191	torben	412	return notifier.getClass().getName();
192	torben	409	}
193	torben	1148
194			public synchronized ExecutorService getExecutor() {
195
196			if (executor == null) {
197			executor = Executors.newFixedThreadPool(1);
198			}
199
200			return executor;
201
202			}
203	torben	397
204	torben	393	}