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// ""Double-Checked Locking"" idiom class Foo { private Helper helper = null; public Helper getHelper() { if (helper == null) { synchronized(this) { if (helper == null) helper = new Helper(); } } return helper; } // other functions and members... } |
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EX1: Explicitly synchronized code does not require the use of double-checked locking.
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*EX2:* ""Although the double-checked locking idiom cannot be used for references to objects, it can work for 32-bit primitive values (e.g., int's or float's). Note that it does not work for long's or double's, since unsynchronized reads/writes of 64-bit primitives are not guaranteed to be atomic."" \[[Pugh 04|AA. Java References#Pugh 04]\] |
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\[[API 06|AA. Java References#API 06]\] \[[Pugh 04|AA. Java References#Pugh 04]\] \[[MITRE 09|AA. Java References#MITRE 09]\] [CWE ID 609|http://cwe.mitre.org/data/definitions/609.html] ""Double-Checked Locking"" |
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FIO36CON42-J. Do not create multiple buffered wrappers on an InputStream 09. Input Output (FIO) 09. Input Output (FIO)Ensure actively held locks are released on exceptional conditions 11. Concurrency (CON) CON44-J. Do not expect sleep() and yield() methods to have any synchronization semantics