After handling a request, a sync read thread polls its /dev/fuse fd for
up to fuse-read-spin-us microseconds before blocking in read(). Default
0 (disabled). Measured at 50us (tmpfs branch, direct_io): sequential
128K/1M reads +27-32%, 128K writes +14%, metadata walks +24-32%; no
change on 8 parallel streams or 1M writes. Costs roughly one core on a
busy-but-quiet mount, nothing when idle.
- Store cloned read-worker fds on fuse_session and close them there.
- Set up clone fallback through session helpers used by the loop.
- Carry per-request fds through receive, process, and reply paths.
Tests show significant performance increases in highly concurrent
workloads on a high core count system. Upto 15% better on reads and
27% on writes.
- ThreadPool::destroy used to iterate _threads directly while another
thread could be adjusting the same vector. Snapshot the vector
under the mutex and iterate the local copy for pthread_cancel /
pthread_join.
- ObjPool::construct now returns NULL when the pooled allocator
returns NULL instead of invoking placement-new on a null
pointer. In destroy, compute to_node(obj) before running the
destructor - the destructor may scrub bytes the to_node helper
reads.
- In the async/sync workers in fuse_loop, msgbuf_alloc can return
NULL under memory pressure. Fail the worker cleanly with a
diagnostic rather than dereferencing. Also introduce a small
_nproc() helper that treats hardware_concurrency()==0 as 1, so
the downstream min/max arithmetic doesn't produce a zero thread
count.
