thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.circuitbreaker;


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

import dk.thoerup.circuitbreaker.config.BreakerConfig;
import dk.thoerup.circuitbreaker.config.StaticConfig;
import dk.thoerup.circuitbreaker.notification.NotiferHelper;
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, int timeoutMS) {
                this(name, new StaticConfig(threshold, timeoutMS) );
        }*/
        
        public CircuitBreaker(String name, BreakerConfig config) {
                closed.setThreshold(config);
                open.setTimeout(config);
                
                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(this, event);
                }
        }       
    }

    public void attemptReset() {
        synchronized(this) {
                if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
                        currentState = halfOpen;
                        notifier.sendNotification(this, Notifier.Event.BreakerAttemptReset);
                }
        }
        
    }
    
    public void reset() {
        synchronized(this) {
                if (currentState != closed) { // TODO: Is this conditional necessary ??
                        internalReset();
                        notifier.sendNotification(this, 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 NotiferHelper.getName(notifier);
    }
    
    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	1306	import dk.thoerup.circuitbreaker.config.BreakerConfig;
8			import dk.thoerup.circuitbreaker.config.StaticConfig;
9	torben	1289	import dk.thoerup.circuitbreaker.notification.NotiferHelper;
10	torben	467	import dk.thoerup.circuitbreaker.notification.Notifier;
11			import dk.thoerup.circuitbreaker.notification.NullNotifier;
12	torben	409
13	torben	394	/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
14			*
15			* example of how it can be used
16	torben	395
17			private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
18			protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
19	torben	393	class TestInvocation implements CircuitInvocation {
20			String url;
21			public TestInvocation(String url) {
22			this.url = url;
23			}
24			public Object proceed() throws Exception{
25
26			URL u = new URL(url);
27			URLConnection c = u.openConnection();
28			c.connect();
29			InputStream in = c.getInputStream();
30			in.close();
31
32
33			return "hello";
34			}
35
36			}
37			try {
38			String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
39			response.getWriter().print(s);
40	torben	452	} catch (Exception e) {
41	torben	393	logger.warning( e.getMessage() );
42			response.sendError(500);
43			return;
44			}
45
46			}
47			*/
48
49
50			public class CircuitBreaker{
51
52	torben	443	private volatile CircuitBreakerState currentState;
53	torben	393
54	torben	424	private final OpenState open = new OpenState();
55			private final HalfOpenState halfOpen = new HalfOpenState();
56			private final ClosedState closed = new ClosedState();
57	torben	393
58			private String name;
59
60	torben	1148	private ExecutorService executor = null;
61	torben	409	private Notifier notifier = new NullNotifier();
62
63	torben	1314	/*public CircuitBreaker(String name, int threshold, int timeoutMS) {
64	torben	1306	this(name, new StaticConfig(threshold, timeoutMS) );
65	torben	1314	}*/
66	torben	1306
67			public CircuitBreaker(String name, BreakerConfig config) {
68			closed.setThreshold(config);
69			open.setTimeout(config);
70	torben	393
71			this.name = name;
72	torben	625
73	torben	627	//set correct intial state
74			internalReset();
75	torben	393	}
76
77	torben	1148	public synchronized void shutdown() {
78			if (executor != null) {
79			executor.shutdown();
80			}
81			}
82	torben	393
83	torben	1148
84	torben	450	public Object invoke(CircuitInvocation invocation) throws Exception
85	torben	393	{
86			Object result = null;
87			try
88			{
89			getState().preInvoke(this);
90			result = invocation.proceed();
91			getState().postInvoke(this);
92			}
93	torben	450	catch(Exception e)
94	torben	393	{
95	torben	450	getState().onError(this, e);
96			throw e;
97	torben	393	}
98			return result;
99			}
100
101			public void tripBreaker() {
102	torben	871	commonTripBreaker(Notifier.Event.BreakerTripped);
103	torben	393	}
104
105	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
106			public void retripBreaker() {
107	torben	871	commonTripBreaker(Notifier.Event.BreakerRetripped);
108			}
109
110			private void commonTripBreaker(Notifier.Event event) {
111			synchronized(this) {
112	torben	864	if (currentState != open) { // TODO:Is this conditional necessary ??
113			open.trip();
114			currentState = open;
115
116	torben	1161	notifier.sendNotification(this, event);
117	torben	864	}
118	torben	871	}
119	torben	864	}
120
121	torben	393	public void attemptReset() {
122			synchronized(this) {
123	torben	426	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
124			currentState = halfOpen;
125	torben	1161	notifier.sendNotification(this, Notifier.Event.BreakerAttemptReset);
126	torben	426	}
127	torben	393	}
128	torben	409
129	torben	393	}
130
131			public void reset() {
132			synchronized(this) {
133	torben	426	if (currentState != closed) { // TODO: Is this conditional necessary ??
134	torben	627	internalReset();
135	torben	1161	notifier.sendNotification(this, Notifier.Event.BreakerReset);
136	torben	426	}
137	torben	393	}
138			}
139
140	torben	627	//This one actually sets the correct closed/reset state
141			private void internalReset() {
142			closed.resetFailureCount();
143			currentState = closed;
144			}
145	torben	397
146	torben	627
147	torben	393	private CircuitBreakerState getState() {
148			synchronized(this) {
149			return currentState;
150			}
151			}
152	torben	397
153	torben	447	public boolean isClosed() {
154			return (getState() == closed);
155			}
156
157			public boolean isOpen() {
158			return (getState() == open);
159			}
160
161	torben	397	public String getName() {
162			return name;
163			}
164
165			public String getStateName() {
166			return getState().getName();
167			}
168
169			public int getThreshold() {
170			return closed.getThreshold();
171			}
172
173	torben	413	public int getTimeout() {
174			return (int)open.getTimeout();
175			}
176
177	torben	397	public int getFailureCount() {
178			if (getState() == closed) {
179			return closed.getFailureCount();
180			} else {
181			return -1;
182			}
183			}
184
185			public long getElapsed() {
186			if (getState() == open) {
187			return open.getElapsed();
188			} else {
189			return -1;
190			}
191			}
192	torben	409
193			public void setNotifier(Notifier notifier) {
194			this.notifier = notifier;
195			}
196
197	torben	1289	public String getNotifierName() {
198			return NotiferHelper.getName(notifier);
199	torben	409	}
200	torben	1148
201			public synchronized ExecutorService getExecutor() {
202
203			if (executor == null) {
204			executor = Executors.newFixedThreadPool(1);
205			}
206
207			return executor;
208
209			}
210	torben	397
211	torben	393	}