60 lines
2.2 KiB
Plaintext
60 lines
2.2 KiB
Plaintext
== Why is this an issue?
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The `Object.wait(...)`, `Object.notify()` and `Object.notifyAll()` methods are used in multithreaded environments to coordinate interdependent tasks that are performed by different threads.
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These methods are not thread-safe and by contract, they require the invoking `Thread` to own the object's monitor.
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If a thread invokes one of these methods without owning the object's monitor an `IllegalMonitorStateException` is thrown.
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== How to fix it
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To become the owner of an object's monitor Java provides the `synchronized` keyword.
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In other words, calling `Object.wait(...)`, `Object.notify()` and `Object.notifyAll()` on a given object should only be done from code synchronized on the same object.
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For example, the call to `someObject.wait(...)` should be wrapped in a `synchronized(someObject){ ... }` block.
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If `wait` or `notify` are invoked on `this`, then the entire method can be marked as `synchronized`.
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=== Code examples
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==== Noncompliant code example
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[source,java,diff-id=1,diff-type=noncompliant]
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----
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private void performSomeAction(Object syncValue) {
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while (!suitableCondition()){
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syncValue.wait(); // Noncompliant, not being inside a `synchronized` block, this will raise an IllegalMonitorStateException
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}
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... // Perform some action
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}
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----
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==== Compliant solution
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[source,java,diff-id=1,diff-type=compliant]
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----
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private void performSomeAction(Object syncValue) {
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synchronized(syncValue) {
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while (!suitableCondition()){
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syncValue.wait(); // Compliant, the `synchronized` block guarantees ownership of syncValue's monitor
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}
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... // Perform some action
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}
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}
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----
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== References
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* https://docs.oracle.com/javase/tutorial/essential/concurrency/syncmeth.html[Java Documentation] - Synchronized methods
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* https://docs.oracle.com/javase%2F7%2Fdocs%2Fapi%2F%2F/java/lang/Object.html#wait()[Java Documentation] - java.lang.Object class and its methods
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Make this call to "[wait(...)|notify()|notifyAll()]" only inside a synchronized block to be sure to hold the monitor on "[this|xxx]" object.
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endif::env-github,rspecator-view[]
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