Two thread-safety bugs in the native FFI layer.
The HTTP server's accept/recv/send were plain foreign-procedures. A thread
inside a foreign call stays active for the stop-the-world collector, so the
accept loop sitting idle in accept() froze GC for the whole process whenever
another thread (a future, an async block) allocated. Mark the three blocking
calls __collect_safe so the thread deactivates for the call's duration —
collection proceeds while the accept thread waits. The args are an fd and
foreign-alloc'd buffers (outside the Scheme heap), so a collection mid-call has
nothing to move.
jolt.http-client built its -D header-file path from an unguarded (set! counter
(+ counter 1)) and counter mod 90000, with no per-process component. Concurrent
requests could compute the same path and clobber each other's headers. Use a
mutex-guarded monotonic counter plus the pid.
test/chez/ffi-server-test.ss exercises both (a (collect) while the server is
idle in accept(), temp-path uniqueness across threads, and a live request) and
is wired into the gate as `make ffi`.
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