Reintorduce gc_disable/enable API#1457
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…g gap Bindings previously had to implement VMCollection::is_collection_enabled() and synchronize enabling/disabling collection across threads themselves. Replace that callback with disable_collection()/enable_collection()/ is_collection_enabled() on MMTK, backed by a nestable, lock-guarded counter in GCTrigger so a GC is never requested while collection is disabled. Also add wait_for_no_collection_in_progress(), which blocks until no GC is pending, mid-pause, or (for concurrent plans, via the existing ConcurrentPlan::concurrent_work_in_progress() hook) concurrently marking. Bindings that need a hard guarantee that no GC touches memory during some unsafe window (e.g. adopting a foreign thread, or recovering from a fatal signal) should call disable_collection() followed by wait_for_no_collection_in_progress(), the MMTk-native equivalent of waiting for an in-flight GC to finish. Without it, a collection that is already mid-cycle when collection is disabled is not affected until it completes, and for concurrent plans that includes the whole concurrent marking phase, not just a stop-the-world pause. Co-authored-by: Claude <noreply@anthropic.com>
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Poll with a yield instead of a fixed sleep between checks, so the calling thread gives up its timeslice without imposing a fixed latency floor on how quickly it notices the collection has finished. Add a regression test: one thread triggers a GC and blocks in block_for_gc (simulating an in-progress collection), while a second thread calls disable_collection() followed by wait_for_no_collection_in_progress() and must remain blocked until the first thread's GC finishes. Also fix two benchmarks (mock_bench/alloc.rs, mock_bench/internal_pointer.rs) that configured the now-removed MockVM::is_collection_enabled field to keep GC out of the way; they now call memory_manager::disable_collection() directly. Co-authored-by: Claude <noreply@anthropic.com>
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