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Workaround a synchronization bug. #772

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Merged
merged 3 commits into from
Mar 9, 2023
Merged

Workaround a synchronization bug. #772

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aa17e49
Workaround a synchronization bug.
wks Mar 8, 2023
c7be6a1
Mention the issues in the comment.
wks Mar 9, 2023
bfd26a4
Merge branch 'master' into fix-gc-termination-simple
wks Mar 9, 2023
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18 changes: 16 additions & 2 deletions src/scheduler/controller.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use std::sync::Arc;

use crate::plan::gc_requester::GCRequester;
use crate::scheduler::gc_work::{EndOfGC, ScheduleCollection};
use crate::scheduler::CoordinatorMessage;
use crate::scheduler::{CoordinatorMessage, GCWork};
use crate::util::VMWorkerThread;
use crate::vm::VMBinding;
use crate::MMTK;
Expand Down Expand Up @@ -131,7 +131,21 @@ impl<VM: VMBinding> GCController<VM> {
let mut end_of_gc = EndOfGC {
elapsed: gc_start.elapsed(),
};
self.initiate_coordinator_work(&mut end_of_gc, false);

// Note: We cannot use `initiate_coordinator_work` here. If we increment the
// `pending_coordinator_packets` counter when a worker spuriously wakes up, it may try to
// open new buckets and result in an assertion error.
// See: https://github.com/mmtk/mmtk-core/issues/770
//
// The `pending_coordinator_packets` counter and the `initiate_coordinator_work` function
// were introduced to prevent any buckets from being opened while `ScheduleCollection` or
// `StopMutators` is being executed. (See the doc comment of `initiate_coordinator_work`.)
// `EndOfGC` doesn't add any new work packets, therefore it does not need this layer of
// synchronization.
//
// FIXME: We should redesign the synchronization mechanism to properly address the opening
// condition of buckets. See: https://github.com/mmtk/mmtk-core/issues/774
end_of_gc.do_work_with_stat(&mut self.coordinator_worker, self.mmtk);

self.scheduler.debug_assert_all_buckets_deactivated();
}
Expand Down