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author | Aleksandar Prokopec <aleksandar.prokopec@gmail.com> | 2015-02-11 20:40:35 +0100 |
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committer | Aleksandar Prokopec <aleksandar.prokopec@gmail.com> | 2015-02-18 23:34:24 +0100 |
commit | da2d4caae990bcb9fabb13e7a242b2b7babe0e0b (patch) | |
tree | 8d972c91aa4a3c4da1f2631689e1fc558cc80fc5 /src/library | |
parent | d14e065eb792a1eb77289f4a1320071c57c5d09b (diff) | |
download | scala-da2d4caae990bcb9fabb13e7a242b2b7babe0e0b.tar.gz scala-da2d4caae990bcb9fabb13e7a242b2b7babe0e0b.tar.bz2 scala-da2d4caae990bcb9fabb13e7a242b2b7babe0e0b.zip |
Fix SI-7943 -- make `TrieMap.getOrElseUpdate` atomic.
Override `getOrElseUpdate` method in `TrieMap`.
The signature and contract of this method corresponds closely to the
`computeIfAbsent` from `java.util.concurrent.ConcurrentMap`.
Eventually, `computeIfAbsent` should be added to
`scala.collection.concurrent.Map`.
Add tests.
Review by @Ichoran
Diffstat (limited to 'src/library')
-rw-r--r-- | src/library/scala/collection/concurrent/TrieMap.scala | 38 | ||||
-rw-r--r-- | src/library/scala/collection/mutable/MapLike.scala | 4 |
2 files changed, 42 insertions, 0 deletions
diff --git a/src/library/scala/collection/concurrent/TrieMap.scala b/src/library/scala/collection/concurrent/TrieMap.scala index fccc1d81b9..bcfea7a463 100644 --- a/src/library/scala/collection/concurrent/TrieMap.scala +++ b/src/library/scala/collection/concurrent/TrieMap.scala @@ -873,6 +873,44 @@ extends scala.collection.concurrent.Map[K, V] insertifhc(k, hc, v, INode.KEY_ABSENT) } + // TODO once computeIfAbsent is added to concurrent.Map, + // move the comment there and tweak the 'at most once' part + /** If the specified key is not already in the map, computes its value using + * the given thunk `op` and enters it into the map. + * + * Since concurrent maps cannot contain `null` for keys or values, + * a `NullPointerException` is thrown if the thunk `op` + * returns `null`. + * + * If the specified mapping function throws an exception, + * that exception is rethrown. + * + * Note: This method will invoke op at most once. + * However, `op` may be invoked without the result being added to the map if + * a concurrent process is also trying to add a value corresponding to the + * same key `k`. + * + * @param k the key to modify + * @param op the expression that computes the value + * @return the newly added value + */ + override def getOrElseUpdate(k: K, op: =>V): V = { + val oldv = lookup(k) + if (oldv != null) oldv.asInstanceOf[V] + else { + val v = op + if (v == null) { + throw new NullPointerException("Concurrent TrieMap values cannot be null.") + } else { + val hc = computeHash(k) + insertifhc(k, hc, v, INode.KEY_ABSENT) match { + case Some(oldv) => oldv + case None => v + } + } + } + } + def remove(k: K, v: V): Boolean = { val hc = computeHash(k) removehc(k, v, hc).nonEmpty diff --git a/src/library/scala/collection/mutable/MapLike.scala b/src/library/scala/collection/mutable/MapLike.scala index af28df1b88..44af886cf5 100644 --- a/src/library/scala/collection/mutable/MapLike.scala +++ b/src/library/scala/collection/mutable/MapLike.scala @@ -178,6 +178,10 @@ trait MapLike[A, B, +This <: MapLike[A, B, This] with Map[A, B]] * * Otherwise, computes value from given expression `op`, stores with key * in map and returns that value. + * + * Concurrent map implementations may evaluate the expression `op` + * multiple times, or may evaluate `op` without inserting the result. + * * @param key the key to test * @param op the computation yielding the value to associate with `key`, if * `key` is previously unbound. |