non-volatile and volatile long and double

Posted 2021-03-23 john123

来源:statckoverflow

Not sure if I understand your question correctly, but the JLS 8.3.1.4. volatile Fields states:

A field may be declared volatile, in which case the Java memory model ensures that all threads see a consistent value for the variable (§17.4).

and, perhaps more importantly, JLS 17.7 Non-atomic Treatment of double and long :

17.7 Non-atomic Treatment of double and long
[...]
For the purposes of the Java programming language memory model, a single write to a non-volatile long or double value is treated as two separate writes: one to each 32-bit half. This can result in a situation where a thread sees the first 32 bits of a 64 bit value from one write, and the second 32 bits from another write. Writes and reads of volatile long and double values are always atomic. Writes to and reads of references are always atomic, regardless of whether they are implemented as 32 or 64 bit values.

That is, the "entire" variable is protected by the volatile modifier, not just the two parts. This tempts me to claim that it‘s even more important to use volatile for longs than it is for ints since not even a read is atomic for non-volatile longs/doubles.