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test(swingset): test liveslots GC with mocks
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Liveslots is not yet calling syscall.dropImports, but by mocking WeakRef and
FinalizationRegistry, we can test to make sure it updates the deadSet
correctly.
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@warner
warner committed Mar 24, 2021
1 parent b67e8ca commit 8fe8077
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Showing 2 changed files with 254 additions and 4 deletions.
15 changes: 12 additions & 3 deletions packages/SwingSet/src/kernel/liveSlots.js
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Original file line number Diff line number Diff line change
Expand Up @@ -132,6 +132,14 @@ function build(
* deadSet holds the vref only in FINALIZED
* re-introduction must ensure the vref is not in the deadSet
Each state thus has a set of perhaps-measurable properties:
* UNKNOWN: slotToVal[vref] is missing, vref not in deadSet
* REACHABLE: slotToVal has live weakref, userspace can reach
* UNREACHABLE: slotToVal has live weakref, userspace cannot reach
* COLLECTED: slotToVal[vref] has dead weakref
* FINALIZED: slotToVal[vref] is missing, vref is in deadSet
Our finalizer callback is queued by the engine's transition from
UNREACHABLE to COLLECTED, but the vref might be re-introduced before the
callback has a chance to run. There might even be multiple copies of the
Expand Down Expand Up @@ -792,7 +800,8 @@ function build(
}

const dispatch = harden({ deliver, notify, dropExports });
return harden({ vatGlobals, setBuildRootObject, dispatch, m });
// we return 'deadSet' for unit tests
return harden({ vatGlobals, setBuildRootObject, dispatch, m, deadSet });
}

/**
Expand Down Expand Up @@ -855,8 +864,8 @@ export function makeLiveSlots(
gcTools,
liveSlotsConsole,
);
const { vatGlobals, dispatch, setBuildRootObject } = r; // omit 'm'
return harden({ vatGlobals, dispatch, setBuildRootObject });
const { vatGlobals, dispatch, setBuildRootObject, deadSet } = r; // omit 'm'
return harden({ vatGlobals, dispatch, setBuildRootObject, deadSet });
}

// for tests
Expand Down
243 changes: 242 additions & 1 deletion packages/SwingSet/test/test-liveslots.js
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Original file line number Diff line number Diff line change
@@ -1,12 +1,15 @@
import { wrapTest } from '@agoric/ses-ava';
import '@agoric/install-ses';
import test from 'ava';
import rawTest from 'ava';
import { E } from '@agoric/eventual-send';
import { Far } from '@agoric/marshal';
import { assert, details as X } from '@agoric/assert';
import { WeakRef, FinalizationRegistry } from '../src/weakref';
import { waitUntilQuiescent } from '../src/waitUntilQuiescent';
import { makeLiveSlots } from '../src/kernel/liveSlots';

const test = wrapTest(rawTest);

function capdata(body, slots = []) {
return harden({ body, slots });
}
Expand Down Expand Up @@ -715,3 +718,241 @@ test('dropExports', async t => {
dispatch.dropExports([ex1]);
// for now, all that we care about is that liveslots doesn't crash
});

// Create a WeakRef/FinalizationRegistry pair that can be manipulated for
// tests. Limitations:
// * only one WeakRef per object
// * no deregister
// * extra debugging properties like FR.countCallbacks and FR.runOneCallback
// * nothing is hardened

function makeMockGC() {
const weakRefToVal = new Map();
const valToWeakRef = new Map();
const allFRs = [];
// eslint-disable-next-line no-unused-vars
function log(...args) {
// console.log(...args);
}

const mockWeakRefProto = {
deref() {
return weakRefToVal.get(this);
},
};
function mockWeakRef(val) {
assert(!valToWeakRef.has(val));
weakRefToVal.set(this, val);
valToWeakRef.set(val, this);
}
mockWeakRef.prototype = mockWeakRefProto;

function kill(val) {
log(`kill`, val);
if (valToWeakRef.has(val)) {
log(` killing weakref`);
const wr = valToWeakRef.get(val);
valToWeakRef.delete(val);
weakRefToVal.delete(wr);
}
for (const fr of allFRs) {
if (fr.registry.has(val)) {
log(` pushed on FR queue, context=`, fr.registry.get(val));
fr.ready.push(val);
}
}
log(` kill done`);
}

const mockFinalizationRegistryProto = {
register(val, context) {
log(`FR.register(context=${context})`);
this.registry.set(val, context);
},
countCallbacks() {
log(`countCallbacks:`);
log(` ready:`, this.ready);
log(` registry:`, this.registry);
return this.ready.length;
},
runOneCallback() {
log(`runOneCallback`);
const val = this.ready.shift();
log(` val:`, val);
assert(this.registry.has(val));
const context = this.registry.get(val);
log(` context:`, context);
this.registry.delete(val);
this.callback(context);
},
};

function mockFinalizationRegistry(callback) {
this.registry = new Map();
this.callback = callback;
this.ready = [];
allFRs.push(this);
}
mockFinalizationRegistry.prototype = mockFinalizationRegistryProto;

function getAllFRs() {
return allFRs;
}

return harden({
WeakRef: mockWeakRef,
FinalizationRegistry: mockFinalizationRegistry,
kill,
getAllFRs,
});
}

test('dropImports', async t => {
const { syscall } = buildSyscall();
const imports = [];
const gcTools = makeMockGC();

function build(_vatPowers) {
const root = Far('root', {
hold(imp) {
imports.push(imp);
},
free() {
gcTools.kill(imports.pop());
},
ignore(imp) {
gcTools.kill(imp);
},
});
return root;
}

const ls = makeLiveSlots(syscall, 'vatA', {}, {}, undefined, false, gcTools);
const { setBuildRootObject, dispatch, deadSet } = ls;
setBuildRootObject(build);
const allFRs = gcTools.getAllFRs();
t.is(allFRs.length, 1);
const FR = allFRs[0];

const rootA = 'o+0';

// immediate drop should push import to deadSet after finalizer runs
dispatch.deliver(rootA, 'ignore', capargsOneSlot('o-1'), null);
await waitUntilQuiescent();
// the immediate gcTools.kill() means that the import should now be in the
// "COLLECTED" state
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);
FR.runOneCallback(); // moves to FINALIZED
t.deepEqual(deadSet, new Set(['o-1']));
deadSet.delete('o-1'); // pretend liveslots did syscall.dropImport

// separate hold and free should do the same
dispatch.deliver(rootA, 'hold', capargsOneSlot('o-2'), null);
await waitUntilQuiescent();
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 0);
dispatch.deliver(rootA, 'free', capargs([]), null);
await waitUntilQuiescent();
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);
FR.runOneCallback(); // moves to FINALIZED
t.deepEqual(deadSet, new Set(['o-2']));
deadSet.delete('o-2'); // pretend liveslots did syscall.dropImport

// re-introduction during COLLECTED should return to REACHABLE

dispatch.deliver(rootA, 'ignore', capargsOneSlot('o-3'), null);
await waitUntilQuiescent();
// now COLLECTED
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);

dispatch.deliver(rootA, 'hold', capargsOneSlot('o-3'), null);
await waitUntilQuiescent();
// back to REACHABLE
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);

FR.runOneCallback(); // stays at REACHABLE
t.deepEqual(deadSet, new Set());

dispatch.deliver(rootA, 'free', capargs([]), null);
await waitUntilQuiescent();
// now COLLECTED
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);

FR.runOneCallback(); // moves to FINALIZED
t.deepEqual(deadSet, new Set(['o-3']));
deadSet.delete('o-3'); // pretend liveslots did syscall.dropImport

// multiple queued finalizers are idempotent, remains REACHABLE

dispatch.deliver(rootA, 'ignore', capargsOneSlot('o-4'), null);
await waitUntilQuiescent();
// now COLLECTED
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);

dispatch.deliver(rootA, 'ignore', capargsOneSlot('o-4'), null);
await waitUntilQuiescent();
// moves to REACHABLE and then back to COLLECTED
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 2);

dispatch.deliver(rootA, 'hold', capargsOneSlot('o-4'), null);
await waitUntilQuiescent();
// back to REACHABLE
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 2);

FR.runOneCallback(); // stays at REACHABLE
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);

FR.runOneCallback(); // stays at REACHABLE
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 0);

// multiple queued finalizers are idempotent, remains FINALIZED

dispatch.deliver(rootA, 'ignore', capargsOneSlot('o-5'), null);
await waitUntilQuiescent();
// now COLLECTED
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);

dispatch.deliver(rootA, 'ignore', capargsOneSlot('o-5'), null);
await waitUntilQuiescent();
// moves to REACHABLE and then back to COLLECTED
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 2);

FR.runOneCallback(); // moves to FINALIZED
t.deepEqual(deadSet, new Set(['o-5']));
t.is(FR.countCallbacks(), 1);

FR.runOneCallback(); // stays at FINALIZED
t.deepEqual(deadSet, new Set(['o-5']));
t.is(FR.countCallbacks(), 0);
deadSet.delete('o-5'); // pretend liveslots did syscall.dropImport

// re-introduction during FINALIZED moves back to REACHABLE

dispatch.deliver(rootA, 'ignore', capargsOneSlot('o-6'), null);
await waitUntilQuiescent();
// moves to REACHABLE and then back to COLLECTED
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 1);

FR.runOneCallback(); // moves to FINALIZED
t.deepEqual(deadSet, new Set(['o-6']));
t.is(FR.countCallbacks(), 0);

dispatch.deliver(rootA, 'hold', capargsOneSlot('o-6'), null);
await waitUntilQuiescent();
// back to REACHABLE, removed from deadSet
t.deepEqual(deadSet, new Set());
t.is(FR.countCallbacks(), 0);
});

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