[dmd-concurrency] A synchronized storage class?

[Michel Fortin]

Le 2010-01-07 à 8:54, Andrei Alexandrescu a écrit :

> We would very much like to _not_ add new qualifiers unless absolutely necessary. Your examples don't express that necessity - if you simply remove the "synchronized" qualifier off i and j, the compiler has enough information to do what's needed.

Sorry, I must be getting tiresome by proposing qualifiers then. I'll refrain from proposing new qualifiers from now on.

You're right that the example doesn't show a necessity for "synchronized" qualifying i and j. But I think the essence remains: member variables explicitly written as being "shared" could stay "shared" even under synchronization, forcing you to use atomic operations. Other member variables could be accessible only from not-shared functions and from shared functions under synchronization.

This would improve thread safety because each variable would have only one way to be accessed when the object is shared, either under synchronization or with atomic operations, but not both.

The downsides are that you can't have a variable which is not shared when the object is not and become "shared but not synchronized" when the object is shared, nor can you synchronize access to shared members in a thread-local object. I don't see how to fix that (without a new storage class), so would those downsides be acceptable? I feel the first one might be too much.

-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/