JDK-4996165 : (spec) weakCompareAndSet has different memory effects from compareAndSet
  • Type: Bug
  • Component: core-libs
  • Sub-Component: java.util.concurrent
  • Affected Version: 5.0
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2004-02-18
  • Updated: 2017-05-16
  • Resolved: 2004-03-04
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Other
5.0 b42Fixed
Description
weakCompareAndSet and compareAndSet are intended to have slightly
different semantics, but this is not correctly specified in
java/util/concurrent/atomic/package.html
Comments
CONVERTED DATA BugTraq+ Release Management Values COMMIT TO FIX: tiger-beta2 FIXED IN: tiger-beta2 INTEGRATED IN: tiger-b42 tiger-beta2
14-06-2004
SUGGESTED FIX --- /tmp/geta21340 2004-02-17 19:03:10.518685000 -0800 +++ package.html 2004-02-17 18:56:05.385307000 -0800 @@ -55,30 +55,34 @@ <pre> class Sequencer { private AtomicLong sequenceNumber = new AtomicLong(0); public long next() { return sequenceNumber.getAndIncrement(); } } </pre> -<p>The memory effects for accesses and updates of atomics follow the +<p>The memory effects for accesses and updates of atomics generally follow the rules for volatiles: <ul> <li> <tt>get</tt> has the memory effects of reading a <tt>volatile</tt> variable. <li> <tt>set</tt> has the memory effects of writing (assigning) a <tt>volatile</tt> variable. - <li> <tt>compareAndSet</tt>, <tt>weakCompareAndSet</tt>, -and other read-and-update operations -have the memory effects of both reading and -writing <tt>volatile</tt> variables. - + <li><tt>weakCompareAndSet</tt> atomically reads and conditionally + writes a variable, is ordered with respect to other + memory operations on that variable, but otherwise acts as an + ordinary non-volatile memory operation. + + <li> <tt>compareAndSet</tt> + and all other read-and-update operations + have the memory effects of both reading and + writing <tt>volatile</tt> variables. </ul> <p>In addition to classes representing single values, this package contains <em>Updater</em> classes that can be used to obtain <tt>compareAndSet</tt> operations on any selected <tt>volatile</tt> field of any selected class. {@link java.util.concurrent.atomic.AtomicReferenceFieldUpdater}, {@link
11-06-2004
PUBLIC COMMENTS (spec) weakCompareAndSet has different memory effects from compareAndSet
10-06-2004
EVALUATION The suggested fix is being provided by the JSR-166 Expert Group. ###@###.### 2004-02-17
17-02-2004