pub fn on_thread_idle()Expand description
Tell mimalloc this thread is idle (issue #272, Bun parity P7a).
Collects this thread’s pending frees, discards the free blocks inside its still-used pages, and hands the arena purge to the background scavenger thread so freed memory returns to the OS now instead of at the next allocation that happens to run a purge – which, on a genuinely idle process, is never.
Safe on any thread; a no-op on a thread that never allocated. Call it when the thread
has nothing to do (an event loop about to block, a worker pool waiting on its queue),
not on a hot path: it costs a few madvise/DiscardVirtualMemory calls.