Transparent interlocking of VHLL fat structures performed automatically by the VM itself. No need for :shared or lock().
Completely specious, and repeatedly proven unwise. Shouldn't even be pursued.
Atomic guarantees on collections (or other data structures) are rarely meaningful; providing them is simply a waste of time. Witness the well-deserved death of Java's synchronized Vector class in favor of ArrayList. The interpreter absolutely shouldn't crash due to threading errors—it should protect itself using standard techniques—but it would be a mistake for parrot to mandate that all ops and PMCs be thread-safe.
The details of threaded programming cannot be hidden from the programmer. It's tempting to come up with clever ways to try, but the engine really has to take a back seat here. Smart programmers will narrow the scope of potential conflicts by reducing sharing of data structures in their threaded programs. Having done so, any atomicity guarantees on individual objects proves to be wasted effort: It will be resented by parrot's users as needless overhead, not praised. Consider the potential usage cases.
1. All objects in a non-threaded program. 2. Unshared objects in a threaded program. 3. Shared objects in a threaded program.
The first two cases will easily comprise 99% of all usage. In only the third case are synchronized objects even conceivably useful, and even then the truth of the matter is that they are of extremely limited utility: Their guarantees are more often than not too fine-grained to provide the high-level guarantees that the programmer truly needs. In light of this, the acquisition of a mutex (even a mutex that's relatively cheap to acquire) to push an element onto an array, or to access a string's data—well, it stops looking so good.
That said, the interpreter can't be allowed to crash due to threading errors. It must protect itself. But should a PerlArray written to concurrently from 2 threads guarantee its state make sense at the end of the program? I say no based upon precedent; the cost is too high.
—
Gordon Henriksen [EMAIL PROTECTED]
