Most backends already mapped Mercury threads to "native" threads in spawn/3,
but it was and remains an implementation detail. spawn_native provides
that behaviour as a documented feature for programs which require it,
including for the low-level C backend.
While we are at it, add a `thread' handle type. It currently holds a
thread identifier (not yet formally exported), but it may also have
other uses such as a handle for a `thread.join' predicate, or a place to
hold result values or uncaught exceptions.
library/thread.m:
Add abstract type `thread'.
Add can_spawn_native.
Add spawn_native/4. It can report failure to start a thread,
which was missing from the spawn/3 interface.
Add spawn/4 to match spawn_native/4, without the native thread
requirement.
Make ML_create_exclusive_thread wait for a success code from
the new thread before continuing.
Reduce accessibility levels in C# and Java helper classes.
runtime/mercury_thread.c:
Make MR_init_thread_inner and MR_setup_engine_for_threads
return errors instead of aborting on failure.
tests/hard_coded/Mercury.options:
tests/hard_coded/Mmakefile:
tests/hard_coded/spawn_native.exp2:
tests/hard_coded/spawn_native.exp:
tests/hard_coded/spawn_native.m:
Add test case.
NEWS:
Announce change.
