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412 lines
11 KiB
Plaintext
412 lines
11 KiB
Plaintext
;; Erlang runtime — scheduler, process records, mailbox queue.
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;; Phase 3 foundation. spawn/send/receive build on these primitives.
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;;
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;; Scheduler is a single global dict in `er-scheduler` holding:
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;; :next-pid INT — counter for fresh pid allocation
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;; :processes DICT — pid-key (string) -> process record
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;; :runnable QUEUE — FIFO of pids ready to run
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;; :current PID — pid currently executing, or nil
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;;
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;; A pid value is tagged: {:tag "pid" :id INT}. Pids compare by id.
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;;
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;; Process record fields:
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;; :pid — this process's pid
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;; :mailbox — queue of received messages (arrival order)
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;; :state — "runnable" | "running" | "waiting" | "exiting" | "dead"
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;; :continuation — saved k (for receive suspension); nil otherwise
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;; :receive-pats — patterns the process is blocked on; nil otherwise
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;; :trap-exit — bool
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;; :links — list of pids
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;; :monitors — list of {:ref :pid}
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;; :env — Erlang env at the last yield
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;; :exit-reason — nil until the process exits
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;;
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;; Queue — amortised-O(1) FIFO with head-pointer + slab-compact:
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;; {:items (list...) :head-idx INT}
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;; ── queue ────────────────────────────────────────────────────────
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(define er-q-new (fn () {:head-idx 0 :items (list)}))
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(define er-q-push! (fn (q x) (append! (get q :items) x)))
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(define
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er-q-pop!
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(fn
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(q)
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(let
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((h (get q :head-idx)) (items (get q :items)))
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(if
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(>= h (len items))
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nil
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(let
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((x (nth items h)))
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(dict-set! q :head-idx (+ h 1))
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(er-q-compact! q)
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x)))))
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(define
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er-q-peek
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(fn
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(q)
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(let
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((h (get q :head-idx)) (items (get q :items)))
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(if (>= h (len items)) nil (nth items h)))))
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(define
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er-q-len
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(fn (q) (- (len (get q :items)) (get q :head-idx))))
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(define er-q-empty? (fn (q) (= (er-q-len q) 0)))
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;; Compact the backing list when the head pointer gets large so the
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;; queue doesn't grow without bound. Threshold chosen to amortise the
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;; O(n) copy — pops are still amortised O(1).
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(define
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er-q-compact!
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(fn
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(q)
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(let
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((h (get q :head-idx)) (items (get q :items)))
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(when
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(> h 128)
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(let
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((new (list)))
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(for-each
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(fn (i) (append! new (nth items i)))
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(range h (len items)))
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(dict-set! q :items new)
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(dict-set! q :head-idx 0))))))
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(define
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er-q-to-list
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(fn
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(q)
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(let
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((h (get q :head-idx)) (items (get q :items)) (out (list)))
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(for-each
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(fn (i) (append! out (nth items i)))
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(range h (len items)))
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out)))
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;; Read the i'th entry (relative to head) without popping.
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(define
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er-q-nth
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(fn (q i) (nth (get q :items) (+ (get q :head-idx) i))))
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;; Remove entry at logical index i, shift tail in.
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(define
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er-q-delete-at!
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(fn
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(q i)
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(let
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((h (get q :head-idx)) (items (get q :items)) (new (list)))
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(for-each
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(fn
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(j)
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(when (not (= j (+ h i))) (append! new (nth items j))))
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(range h (len items)))
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(dict-set! q :items new)
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(dict-set! q :head-idx 0))))
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;; ── pids ─────────────────────────────────────────────────────────
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(define er-mk-pid (fn (id) {:id id :tag "pid"}))
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(define er-pid? (fn (v) (er-is-tagged? v "pid")))
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(define er-pid-id (fn (pid) (get pid :id)))
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(define er-pid-key (fn (pid) (str "p" (er-pid-id pid))))
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(define
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er-pid-equal?
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(fn (a b) (and (er-pid? a) (er-pid? b) (= (er-pid-id a) (er-pid-id b)))))
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;; ── scheduler state ──────────────────────────────────────────────
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(define er-scheduler (list nil))
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(define
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er-sched-init!
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(fn
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()
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(set-nth!
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er-scheduler
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0
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{:next-pid 0
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:current nil
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:processes {}
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:runnable (er-q-new)})))
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(define er-sched (fn () (nth er-scheduler 0)))
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(define
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er-pid-new!
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(fn
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()
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(let
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((s (er-sched)))
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(let
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((n (get s :next-pid)))
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(dict-set! s :next-pid (+ n 1))
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(er-mk-pid n)))))
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(define
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er-sched-runnable
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(fn () (get (er-sched) :runnable)))
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(define
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er-sched-processes
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(fn () (get (er-sched) :processes)))
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(define
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er-sched-enqueue!
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(fn (pid) (er-q-push! (er-sched-runnable) pid)))
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(define
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er-sched-next-runnable!
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(fn () (er-q-pop! (er-sched-runnable))))
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(define
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er-sched-runnable-count
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(fn () (er-q-len (er-sched-runnable))))
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(define
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er-sched-set-current!
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(fn (pid) (dict-set! (er-sched) :current pid)))
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(define er-sched-current-pid (fn () (get (er-sched) :current)))
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(define
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er-sched-process-count
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(fn () (len (keys (er-sched-processes)))))
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;; ── process records ──────────────────────────────────────────────
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(define
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er-proc-new!
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(fn
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(env)
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(let
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((pid (er-pid-new!)))
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(let
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((proc
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{:pid pid
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:env env
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:links (list)
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:mailbox (er-q-new)
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:state "runnable"
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:monitors (list)
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:continuation nil
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:receive-pats nil
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:trap-exit false
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:has-timeout false
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:timed-out false
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:exit-reason nil}))
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(dict-set! (er-sched-processes) (er-pid-key pid) proc)
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(er-sched-enqueue! pid)
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proc))))
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(define
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er-proc-get
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(fn (pid) (get (er-sched-processes) (er-pid-key pid))))
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(define
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er-proc-exists?
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(fn (pid) (dict-has? (er-sched-processes) (er-pid-key pid))))
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(define
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er-proc-field
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(fn (pid field) (get (er-proc-get pid) field)))
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(define
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er-proc-set!
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(fn
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(pid field val)
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(let
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((p (er-proc-get pid)))
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(if
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(= p nil)
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(error (str "Erlang: no such process " (er-pid-key pid)))
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(dict-set! p field val)))))
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(define
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er-proc-mailbox-push!
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(fn (pid msg) (er-q-push! (er-proc-field pid :mailbox) msg)))
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(define
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er-proc-mailbox-size
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(fn (pid) (er-q-len (er-proc-field pid :mailbox))))
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;; Main process is always pid 0 (scheduler starts with next-pid 0 and
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;; erlang-eval-ast calls er-proc-new! first). Returns nil if no eval
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;; has run.
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(define
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er-main-pid
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(fn () (er-mk-pid 0)))
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(define
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er-last-main-exit-reason
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(fn
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()
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(if
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(er-proc-exists? (er-main-pid))
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(er-proc-field (er-main-pid) :exit-reason)
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nil)))
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;; ── process BIFs ────────────────────────────────────────────────
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(define
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er-bif-is-pid
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(fn (vs) (er-bool (er-pid? (er-bif-arg1 vs "is_pid")))))
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(define
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er-bif-self
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(fn
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(vs)
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(if
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(not (= (len vs) 0))
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(error "Erlang: self/0: arity")
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(let
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((pid (er-sched-current-pid)))
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(if
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(= pid nil)
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(error "Erlang: self/0: no current process")
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pid)))))
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(define
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er-bif-spawn
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(fn
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(vs)
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(cond
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(= (len vs) 1) (er-spawn-fun (nth vs 0))
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(= (len vs) 3) (error
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"Erlang: spawn/3: module-based spawn deferred to Phase 5 (modules)")
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:else (error "Erlang: spawn: wrong arity"))))
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(define
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er-spawn-fun
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(fn
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(fv)
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(if
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(not (er-fun? fv))
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(error "Erlang: spawn/1: not a fun")
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(let
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((proc (er-proc-new! (er-env-new))))
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(dict-set! proc :initial-fun fv)
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(get proc :pid)))))
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(define
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er-bif-exit
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(fn
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(vs)
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(cond
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(= (len vs) 1) (raise (er-mk-exit-marker (nth vs 0)))
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(= (len vs) 2)
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(error
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"Erlang: exit/2 (signal another process) deferred to Phase 4 (links)")
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:else (error "Erlang: exit: wrong arity"))))
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;; ── scheduler loop ──────────────────────────────────────────────
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;; Each scheduler step wraps the process body in `guard`. `receive`
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;; with no match captures a `call/cc` continuation onto the proc
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;; record and then `raise`s `er-suspend-marker`; the guard catches
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;; the raise and the scheduler moves on. `exit/1` raises an exit
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;; marker the same way. Resumption from a saved continuation also
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;; runs under a fresh `guard` so a resumed receive that needs to
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;; suspend again has a handler to unwind to. `shift`/`reset` aren't
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;; usable here because SX's captured delimited continuations don't
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;; re-establish their own reset boundary when invoked — a second
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;; suspension during replay raises "shift without enclosing reset".
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(define er-suspend-marker {:tag "er-suspend-marker"})
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(define
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er-suspended?
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(fn
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(v)
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(and
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(= (type-of v) "dict")
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(= (get v :tag) "er-suspend-marker"))))
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(define
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er-exited?
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(fn
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(v)
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(and
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(= (type-of v) "dict")
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(= (get v :tag) "er-exit-marker"))))
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(define
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er-mk-exit-marker
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(fn (reason) {:tag "er-exit-marker" :reason reason}))
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(define
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er-sched-run-all!
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(fn
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()
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(let
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((pid (er-sched-next-runnable!)))
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(cond
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(not (= pid nil))
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(do (er-sched-step! pid) (er-sched-run-all!))
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;; Queue empty — fire one pending receive-with-timeout and go again.
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(er-sched-fire-one-timeout!) (er-sched-run-all!)
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:else nil))))
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;; Wake one waiting process whose receive had an `after Ms` clause.
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;; Returns true if one fired. In our synchronous model "time passes"
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;; once the runnable queue drains — timeouts only fire then.
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(define
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er-sched-fire-one-timeout!
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(fn
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()
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(let
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((ks (keys (er-sched-processes))) (fired (list false)))
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(for-each
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(fn
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(k)
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(when
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(not (nth fired 0))
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(let
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((p (get (er-sched-processes) k)))
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(when
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(and
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(= (get p :state) "waiting")
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(get p :has-timeout))
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(dict-set! p :timed-out true)
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(dict-set! p :has-timeout false)
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(dict-set! p :state "runnable")
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(er-sched-enqueue! (get p :pid))
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(set-nth! fired 0 true)))))
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ks)
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(nth fired 0))))
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(define
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er-sched-step!
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(fn
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(pid)
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(er-sched-set-current! pid)
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(er-proc-set! pid :state "running")
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(let
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((prev-k (er-proc-field pid :continuation))
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(result-ref (list nil)))
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(guard
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(c
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((er-suspended? c) (set-nth! result-ref 0 c))
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((er-exited? c) (set-nth! result-ref 0 c)))
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(set-nth!
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result-ref
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0
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(if
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(= prev-k nil)
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(er-apply-fun (er-proc-field pid :initial-fun) (list))
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(do (er-proc-set! pid :continuation nil) (prev-k nil)))))
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(let
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((r (nth result-ref 0)))
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(cond
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(er-suspended? r) nil
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(er-exited? r)
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(do
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(er-proc-set! pid :state "dead")
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(er-proc-set! pid :exit-reason (get r :reason))
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(er-proc-set! pid :exit-result nil)
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(er-proc-set! pid :continuation nil))
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:else (do
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(er-proc-set! pid :state "dead")
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(er-proc-set! pid :exit-reason (er-mk-atom "normal"))
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(er-proc-set! pid :exit-result r)
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(er-proc-set! pid :continuation nil)))))
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(er-sched-set-current! nil)))
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