On Sunday, 31 August 2025 at 03:45:07 UTC, Ali Çehreli wrote:
On 8/30/25 6:34 PM, Steven Schveighoffer wrote:
> The original feature never worked as intended. That section
of the book
> should be removed.
>
> The correct way to do this is a nested synchronized statement:
>
> ```d
> synchronized(from) synchronized(to)
> {
> ...
> }
> ```
That's a recipe for a deadlock though: Imagine the same
function is running for two bank accounts (A and B), each
sending money to each other.
In one case, 'from' is A, and 'to' is B. In the other case,
'from' is B, and 'to' is A.
One thread locks A and the other locks B, then they both wait
for the other forever.
When the language lacks a canonical order for multiple locks,
the programmer must come up with a scheme to sort them and
attempt to lock in the same order in both threads.
D has never supported this.
From the book:
Note: This feature is not supported by dmd 2.098.1.
This should read:
Note: this feature has never been implemented and before DMD
2.098.1 this syntax would compile and do the wrong thing.
Which is why I recommend removing the whole discussion.
If you want to ensure some order of locking you need to do it
manually. Even before 2.098.1
-Steve
