Robert Allan JamesandClaude Sonnet 5
66beae7fd4
Implements the message-arrival eligibility signal FABRIC-3.md §XXVIII.1 left open (has_work per-slot flag, set via new SWITCH-MARK-WORK primitive from MSG-SEND) so an idle VM never becomes a switch target purely by waiting out the readiness threshold. Also root-causes and fixes a second, independent switch-storm: the tick's "who is current" check used vm_log_attributed_vm(), which can't see a VM parked in switch.c's own raw trampoline. Replaced with a dedicated g_switch_current_vm tracked by the switch mechanism itself, and moved target-slot eligibility reset to the switch decision point instead of relying on ISR polling to observe a window that can be only a few instructions wide. Verified live on all 3 architectures: clean boot to zuse@Hera] ok>, live cross-VM message dispatch, and (since a quiet log looks identical to a livelocked storm once the DoE probe is gone) confirmed genuine REPL liveness via QMP send-key + screendump on aarch64/riscv64, not log inspection alone. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01BWpNjdwPtFLuVLaAq44L9K
110 lines
5.1 KiB
C
110 lines
5.1 KiB
C
/*
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StarForth — Steady-State Virtual Machine Runtime
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Copyright (c) 2023–2025 Robert A. James
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All rights reserved.
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This file is part of the StarForth project.
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Licensed under the StarForth License, Version 1.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at:
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https://github.com/star.4th@proton.me/StarForth/LICENSE.txt
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This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
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express or implied, including but not limited to the warranties of
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merchantability, fitness for a particular purpose, and noninfringement.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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/**
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* capsule_vm_switch_signal.h - New, purpose-built "who runs next" signal
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* for preemptive context switching (FABRIC-3.md §XXVIII, Stage 3,
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* 2026-09-13).
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*
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* Deliberately NOT a repurposing of capsule_vm_physics.c's execution-heat
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* engine -- that measures word-level dispatch fairness over millions of
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* executions on a different timescale, and its own header explicitly
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* documents it as never touched from interrupt context (unlocked, by
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* design). This is a different physical quantity: instant-by-instant
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* run-readiness, consulted from real ISR context (heartbeat_tick()) every
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* timer tick.
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*
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* Concurrency discipline mirrors heartbeat.c's own §21.1-sanctioned
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* pattern for heartbeat_next_period_ns(): single-writer-ISR (tick()) /
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* single-reader-mainline (take_pending(), called from the cooperative
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* checkpoint in execute_colon_word()), no lock, because nothing on this
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* single hart is concurrent with the ISR while it runs.
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*
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* NOT truly interrupt-driven register/stack swapping (that was
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* considered and rejected for this stage -- see FABRIC-3.md §XXVIII
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* Stage 3 for why): the ISR only ever sets a flag. The actual switch
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* (Stage 2's already-proven sk_vm_context_switch()) happens later, at a
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* safe cooperative checkpoint on the mainline, once per word dispatch.
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*
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* Slot table is sized with headroom, not hardcoded to exactly today's 3
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* participants (Hera/Hermes/Artemis) -- extending participation later
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* (Stage 4+) is another sk_vm_switch_signal_register() call, not a
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* redesign.
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*/
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#ifndef STARKERNEL_CAPSULE_VM_SWITCH_SIGNAL_H
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#define STARKERNEL_CAPSULE_VM_SWITCH_SIGNAL_H
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#ifdef __STARKERNEL__
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#include <stdint.h>
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#include "starkernel/vm_uuid.h"
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/* Register a VM as a switch-signal participant. Returns its slot index,
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* or -1 if the slot table is full. Call once per participating VM,
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* after that VM is fully born (never mid-birth -- this stage has no
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* critical-section protection against being switched away mid-setup). */
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int sk_vm_switch_signal_register(VMUuid vm_id);
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/* Called from heartbeat_tick() (ISR context) every timer tick. Cheap:
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* iterates only the registered slots (bounded, small). */
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void sk_vm_switch_signal_tick(void);
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/* Called from the cooperative checkpoint (execute_colon_word(), mainline,
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* once per word dispatch). Returns the VMUuid of a VM that should now be
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* switched to, or vm_uuid_none() if nothing is pending. Clears the
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* pending flag as a side effect -- call at most once per checkpoint. */
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VMUuid sk_vm_switch_signal_take_pending(void);
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/* Call once, from the same checkpoint, immediately after a switch
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* sk_vm_switch_signal_take_pending() requested actually executes (not if
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* the target turned out invalid/self) -- feeds the DoE CSV counters
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* below. Also resets `target_id`'s own readiness/has_work directly
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* (Stage 3 follow-on correction, 2026-09-14) -- see the .c file's own doc
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* comment on why this can't be left to tick()'s current-slot polling. */
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void sk_vm_switch_signal_note_switch_performed(VMUuid target_id);
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/* Message-arrival eligibility hook (FABRIC-3.md §XXVIII Stage 3 follow-on,
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* 2026-09-14): mark that VM `vm_id` was just sent a message (the FORTH-side
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* MSG-SEND hook in capsules/common/messaging.4th calls this via the new
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* SWITCH-MARK-WORK primitive, mainline, single-writer). Consulted by
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* sk_vm_switch_signal_tick()'s own readiness->pending decision so a VM
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* with nothing recently sent to it never becomes a switch target purely by
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* sitting idle long enough -- closes the wasteful (but, since the Stage 3
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* stack-ownership fix, no longer corrupting) trampoline-bounce cycle for
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* an idle participant. No-op for an unregistered vm_id. */
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void sk_vm_switch_signal_mark_work(VMUuid vm_id);
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/* DoE CSV read-only exposure (FABRIC-3.md §XXVIII Stage 3 follow-on,
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* 2026-09-13) -- all of this state already existed for the switch
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* decision itself; these just make it observable. */
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uint64_t sk_vm_switch_signal_switch_count(void); /* cumulative, since boot */
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uint32_t sk_vm_switch_signal_ticks_since_switch(void);
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int sk_vm_switch_signal_current_slot(void); /* -1 = none/unregistered */
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int sk_vm_switch_signal_slot_count(void);
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uint32_t sk_vm_switch_signal_readiness(int slot); /* 0 if slot out of range */
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uint32_t sk_vm_switch_signal_readiness_of(VMUuid vm_id); /* 0 if not registered */
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#endif /* __STARKERNEL__ */
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#endif /* STARKERNEL_CAPSULE_VM_SWITCH_SIGNAL_H */
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