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8231592: Clarify that ConcurrentHashMap compute methods mapping functions execute at most once

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Reviewed-by: martin
This commit is contained in:
Doug Lea 2019-11-01 09:04:04 -07:00
parent b56749537d
commit dc7d30d08e
10 changed files with 109 additions and 30 deletions
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34
src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java
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@ -1667,11 +1667,14 @@ public class ConcurrentHashMap<K,V> extends AbstractMap<K,V>
* If the specified key is not already associated with a value,
* attempts to compute its value using the given mapping function
* and enters it into this map unless {@code null}. The entire
* method invocation is performed atomically, so the function is
* applied at most once per key. Some attempted update operations
* on this map by other threads may be blocked while computation
* is in progress, so the computation should be short and simple,
* and must not attempt to update any other mappings of this map.
* method invocation is performed atomically. The supplied
* function is invoked exactly once per invocation of this method
* if the key is absent, else not at all. Some attempted update
* operations on this map by other threads may be blocked while
* computation is in progress, so the computation should be short
* and simple.
*
* <p>The mapping function must not modify this map during computation.
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
@ -1778,10 +1781,13 @@ public class ConcurrentHashMap<K,V> extends AbstractMap<K,V>
* If the value for the specified key is present, attempts to
* compute a new mapping given the key and its current mapped
* value. The entire method invocation is performed atomically.
* Some attempted update operations on this map by other threads
* may be blocked while computation is in progress, so the
* computation should be short and simple, and must not attempt to
* update any other mappings of this map.
* The supplied function is invoked exactly once per invocation of
* this method if the key is present, else not at all. Some
* attempted update operations on this map by other threads may be
* blocked while computation is in progress, so the computation
* should be short and simple.
*
* <p>The remapping function must not modify this map during computation.
*
* @param key key with which a value may be associated
* @param remappingFunction the function to compute a value
@ -1870,10 +1876,12 @@ public class ConcurrentHashMap<K,V> extends AbstractMap<K,V>
* Attempts to compute a mapping for the specified key and its
* current mapped value (or {@code null} if there is no current
* mapping). The entire method invocation is performed atomically.
* Some attempted update operations on this map by other threads
* may be blocked while computation is in progress, so the
* computation should be short and simple, and must not attempt to
* update any other mappings of this Map.
* The supplied function is invoked exactly once per invocation of
* this method. Some attempted update operations on this map by
* other threads may be blocked while computation is in progress,
* so the computation should be short and simple.
*
* <p>The remapping function must not modify this map during computation.
*
* @param key key with which the specified value is to be associated
* @param remappingFunction the function to compute a value