Heap destruction uses CollectEverything to synchronously free every live
cell. Empty blocks from that pass do not need deferred madvise work.
Registering them with the global decommit worker can start a detached
thread during process teardown. LeakSanitizer can then hang while doing
its final thread scan with log_threads enabled.
Let full sweep deallocation opt out of deferred decommit registration.
Normal incremental sweeping stays on the background worker path. The
sanitizer LibGC container and visitor tests now exit with verbose LSan
thread logging enabled.
This commit splits out synchronization primitives from LibThreading into
LibSync. This is because LibThreading depends on LibCore, while LibCore
needs the synchronization primitives from LibThreading. This worked
while they were header only, but when I tried to add an implementation
file it ran into the circular dependency. To abstract away the pthread
implementation using cpp files is necessary so the synchronization
primitives were moved to a separate library.
deallocate_block() used to call MADV_FREE_REUSABLE / MADV_FREE /
MADV_DONTNEED inline on every freed block. With sweep typically
freeing many blocks per GC, the cumulative syscall cost shows up
as real GC pause time.
Move the work onto a single global "decommit worker" thread:
- deallocate_block now just poisons the slot and pushes it onto a
per-allocator m_freshly_freed queue. No syscalls.
- allocate_block prefers m_freshly_freed over m_blocks, so a slot
that's recycled before the worker sees it skips the
REUSABLE/REUSE pair entirely. This is the main payoff.
- Heap::sweep_dead_cells kicks the worker at the end of sweep.
The worker sleeps 50 ms after each kick to give the JS thread
breathing room, then drains each registered allocator's
m_freshly_freed, madvises slots in batches of 64 with
sched_yield between batches, and splices them onto m_blocks.
- Per-allocator refcount + condvar lets ~BlockAllocator wait
until the worker has dropped its reference before our storage
goes away. (Chunks themselves remain leaked: type-isolated VM
is permanent, so we never tear them down.)
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
2024-11-15 14:49:20 +01:00
Renamed from Libraries/LibJS/Heap/BlockAllocator.h (Browse further)
