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Fast functional circuit-breaker written in Clojure
krukow/clojure-circuit-breaker
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Functional Implementation of Michael Nygaard's circuit breaker stability pattern using Clojure protocols and data types A circuit breaker acts as an intemediary between a caller and a callee. Typically the callee is an interface to an integration point, and the caller is a client of that integration point. If the circuit breaker detects a number of failures in the callee it 'trips' (i.e., transitions to the open state) and prevents further calls to the callee for a fixed period (fail fast). After this period it lets a single call go though and transitions to the initial state or back to the open state depending on the outcome. The circuit breaker is parameterized by a policy that decides * how many failures are needed to trip * how long before letting the single probe call pass * what type of Exceptions from the integration point should be considered errors to the circuit breaker (e.g., one may want to exclude security related exceptions) --------- The implementation uses Clojure protocols and records (data type) to implement a functional state machine. The current state of a circuitbreaker is held in a clojure atom, to updating is lock-free. States are immutable (record) objects that satisfy the CircuitBreakerTransitions protocol. The protocol functions are pure (transition) functions that map a state to a new state. This implementation is easy to use from Java. For an example see src/C.java and notes below. Compiling. Use leiningen 1.3.x. krukow:~/Projects/clojure/circuitbreaker$ lein compile Listening for transport dt_socket at address: 8030 Compiling net.higher-order.integration.circuit-breaker.states Compiling net.higher-order.integration.circuit-breaker.atomic Compiling net.higher-order.integration.circuit-breaker.java Compiling net.higher-order.integration.circuit-breaker.java.AtomicCircuitBreaker To compile Java example. krukow:~/Projects/clojure/circuitbreaker$ javac -cp lib/*:src:classes src/C.java -d classes/ To run: krukow:~/Projects/clojure/circuitbreaker$ java -cp lib/*:src:classes C Invoked with: KARL KARL Invoked with: 42 42 #:net.higher-order.integration.circuit-breaker.states.ClosedState{:policy #:net.higher-order.integration.circuit-breaker.states.TransitionPolicy{:max-fail-count 5, :timeout 5000, :is-error #<states$make_transition_policy$fn__91 net.higher_order.integration.circuit_breaker.states$make_transition_policy$fn__91@67c7980c>}, :fail-count 0} null arg ... krukow:~/Projects/clojure/circuitbreaker$
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