Srinivasa Chary

• May 4th, 2006

 

The volatile keyword is used on variables that may be modified simultaneously by other threads. This warns the compiler to fetch them fresh each time, rather than caching them in registers. This also inhibits certain optimisations that assume no other thread will change the values unexpectedly. Since other threads cannot see local variables, there is never any need to mark local variables volatile.

Thakkar Nirav

 Profile Answers by Thakkar Nirav Questions by Thakkar Nirav

• May 6th, 2006

 

During execution, compiled code might cache the values of fields for efficiency reasons. Since multiple threads can access the same field, it is vital that caching is not allowed to cause inconsistencies when reading and writing the value in the field. The volatile modifier can be used to inform the compiler that it should not attempt to perform optimizations on the field, which could cause unpredictable results when the field is accessed by multiple threads.In the simple example that follows, the value of the field clockReading might be changed unexpectedly by another thread while one thread is performing a task that involves always using the current value of the field clockReading. Declaring the field as volatile ensures that a write operation will always be performed on the master field variable, and a read operation will always return the correct current value.class VitalControl { // ... volatile long clockReading; // Two successive reads might give different results.}