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This approach may not be used when a getter method performs operations other than just returning the value of a {{volatile}} field without having to use any synchronization. Unless read performance is critical, this technique may not offer significant advantages over synchronization \[[Goetz 06|AA. Java References#Goetz 06]\]. |
The guideline CON11-J. Do not assume that declaring an object reference volatile guarantees visibility of its members also addresses the volatile-read, synchronized-write pattern.
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The @RegionLock annotation creates a locking policy, named FlagLock, that specifies that reads and writes to the flag field are to be guarded by a lock on the receiver, that is, this. The second annotation, @Promise is used to place an annotation on the default constructor generated by the compiler. The @Unique("return") annotation promises that the receiver is not aliased during object construction, that is, that a race condition cannot occur during construction. (The guideline CON14-J. Do not let the "this" reference escape during object construction provides further details.) If the constructor was explicit in the code, the annotations would be as follows:
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