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ninjudd committed Feb 2, 2011
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  1. +8 −0 .gitignore
  2. +227 −0 LICENSE
  3. +11 −0 README.md
  4. +3 −0 project.clj
  5. +86 −0 src/tractor/#transaction.clj#
  6. +1 −0 src/tractor/.#transaction.clj
  7. +85 −0 src/tractor/transaction.clj
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+.cake
+pom.xml
+*.jar
+*.war
+lib
+classes
+build
+/tractor
227 LICENSE
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+Eclipse Public License - v 1.0
+
+THE ACCOMPANYING PROGRAM IS PROVIDED UNDER THE TERMS OF THIS ECLIPSE
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+Tractor is a protocol for implementing revisioned transactions in Clojure.
+
+It is used internally by [TrafficDB](http://github.com/ninjudd/trafficdb) and
+[HOV](http://github.com/lancepantz/hov).
+
+## Installation
+
+The easiest way to use Tractor in your project is via [Cake](http://github.com/ninjudd/cake) or Lein.
+Add the following to the `:dependencies` key in your `project.clj`:
+
+ [tractor "0.5.0-SNAPSHOT"]
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+(defproject tractor "0.5.0-SNAPSHOT"
+ :description "A protocol for revisioned transactions in Clojure."
+ :dependencies [[clojure "1.2.0"]])
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+(ns tractor.transaction)
+
+(def ^{:dynamic true} *transactions* #{})
+(def ^{:dynamic true} *revision* #{})
+
+(defprotocol Transactional
+ (txn-wrap [obj f] "Wrap the given function in a transaction, returning a new function."))
+
+(defprotocol TransactionalSplit
+ (txn-begin [obj] "Begin a new transaction.")
+ (txn-commit [obj] "Commit the current transaction.")
+ (txn-rollback [obj] "Rollback the current transaction."))
+
+(defprotocol Revisioned
+ (get-revision [obj] "Returns the current revision.")
+ (set-revision! [obj rev] "Set the current revision to rev."))
+
+(defmacro at-revision
+ "Execute the given forms with the curren revision set to rev. Can be used to mark changes with a given
+ revision, or read the state at a given revision."
+ [rev & forms]
+ `(binding [*revision* ~rev]
+ ~@forms))
+
+(defn- skip-past-revisions
+ "Wraps the given function in a new function that skips it if the current revision has already
+ been applied, also setting the revision upon executing the function."
+ [layer f]
+ (fn []
+ (if-not layer/*rev*
+ (f)
+ (let [rev (or (get-revision obj) 0)]
+ (if (<= *revision* rev)
+ (printf "skipping revision: revision [%s] <= current revision [%s]\n" layer/*rev* rev)
+ (let [result (f)]
+ (if *revision*
+ (set-revision! obj rev))
+ result))))))
+
+(defn- ignore-nested-transactions
+ "Takes two functions, one that's wrapped in a transaction and one that's not, returning a new fn
+ that calls the transactional fn if not currently in a transaction or otherwise calls the plain fn."
+ [obj f f-txn]
+ (fn []
+ (if (contains? *transactions* obj)
+ (f)
+ (binding [*transactions* (conj *transactions* obj)]
+ (f-txn)))))
+
+(defn- catch-rollbacks
+ "Takes a function and wraps it in a new function that catches the exception thrown by abort-transaction."
+ [f]
+ (fn []
+ (try (f)
+ (catch javax.transaction.TransactionRolledbackException e))))
+
+(defn- wrap-txn-split [obj f]
+ (fn []
+ (txn-begin obj)
+ (try (let [result (f)]
+ (txn-commit obj)
+ result)
+ (catch Throwable e
+ (txn-abort obj)
+ (throw e)))))
+
+(defn wrap-transaction
+ "Takes a function and returns a new function wrapped in a transaction on the given object."
+ [obj f]
+ (->> (if (satisfies? Transactional obj)
+ (wrap-txn obj f)
+ (wrap-txn-split obj f))
+ (catch-rollbacks)
+ (skip-past-revisions obj)
+ (ignore-nested-transactions obj f)))
+
+(defmacro with-transaction
+ "Execute forms withing a transaction on the named layer."
+ [obj & forms]
+ `((wrap-transaction ~obj (fn [] ~@forms))))
+
+(defn abort-transaction
+ "Throws an exception that will be caught by catch-rollbacks to abort the transaction."
+ []
+ (throw (javax.transaction.TransactionRolledbackException.)))
+e
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