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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