On Tue, 12 Oct 2010, Igor Stasenko wrote:
Hello, i just thought, that it would be cool to have a special bytecode, which guarantees atomicity for swapping values between two variables.
To swap two values, you usually do:
| var1 var2 temp |
temp := var1. var1 := var2. var2 := temp.
But since its non-atomic, a process can be interrupted and such operation is not thread-safe.
In order to make it thread safe, you must add even more boilerplate:
| var1 var2 temp |
semaphore critical: [ temp := var1. var1 := var2. var2 := temp. ]
An alternative solution: | a b | a := 1. b := 2. [ | tmp | tmp := a. a := b. b := tmp ] valueUnpreemptively Levente
So, i thought , if we could have a special bytecode, then we could write something like:
| var1 var2 |
var1 :=: var2.
So, VM will guarantee that values of var1 and var2 will be swapped atomically, and completely thread-safe.
var1 and var2 could be either temps or instance variables, but of course not arguments, since they are not assignable.
One thing i don't like, that it will need to introduce a new syntax for atomic-value-swap operator - :=:
Or, maybe just reserve a special keyword selector (which is recognized by compiler), so
var1 __atomicSwapWith: var2
so it will look like a regular smalltalk syntax, except that its not a message send, but a low-level operation instead.
-- Best regards, Igor Stasenko AKA sig.
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