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async_hooks: fix nested hooks mutation #14143

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async_hooks: fix nested hooks mutation #14143

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a4cca58
async_hooks: move restoreTmpHooks call to init
BridgeAR Jul 3, 2017
19890ce
fixup: use fs instead of crypto
BridgeAR Jul 11, 2017
3e5d7ba
async_hooks: fix nested hooks mutation
AndreasMadsen Jul 9, 2017
65d4760
[squash] lint
AndreasMadsen Jul 10, 2017
d04802b
[squash] don't use crypto
AndreasMadsen Jul 10, 2017
0b80a31
[squash] use finally block
AndreasMadsen Jul 10, 2017
cbd1f78
[squash] update comment
AndreasMadsen Jul 13, 2017
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32 changes: 20 additions & 12 deletions lib/async_hooks.js
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ var active_hooks_array = [];
// Track whether a hook callback is currently being processed. Used to make
// sure active_hooks_array isn't altered in mid execution if another hook is
// added or removed.
var processing_hook = false;
var processing_hook = 0;
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Possibly change comment above from simply

Track whether a hook [...]

to something like

Use a counter to track [...] and prevent nested calls [...]

// Use to temporarily store and updated active_hooks_array if the user enables
// or disables a hook while hooks are being processed.
var tmp_active_hooks_array = null;
Expand Down Expand Up @@ -151,7 +151,7 @@ class AsyncHook {


function getHookArrays() {
if (!processing_hook)
if (processing_hook === 0)
return [active_hooks_array, async_hook_fields];
// If this hook is being enabled while in the middle of processing the array
// of currently active hooks then duplicate the current set of active hooks
Expand Down Expand Up @@ -335,19 +335,14 @@ function emitInitS(asyncId, type, triggerAsyncId, resource) {
throw new RangeError('triggerAsyncId must be an unsigned integer');

init(asyncId, type, triggerAsyncId, resource);

// Isn't null if hooks were added/removed while the hooks were running.
if (tmp_active_hooks_array !== null) {
restoreTmpHooks();
}
}

function emitHookFactory(symbol, name) {
// Called from native. The asyncId stack handling is taken care of there
// before this is called.
// eslint-disable-next-line func-style
const fn = function(asyncId) {
processing_hook = true;
processing_hook += 1;
// Use a single try/catch for all hook to avoid setting up one per
// iteration.
try {
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I'm worried that doing reference counting is too fragile.
Why not replace the for either with a .forEach for with a for (const hook of Array.from(active_hooks_array))

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@AndreasMadsen AndreasMadsen Jul 10, 2017 •
edited
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I'm worried that doing reference counting is too fragile.

Could you be more explicit?

edit: Just to avoid confusion, this is not a reference counting it is a depth counting.

Why not replace the for either with a .forEach

.forEach is not resistant to mutation.

const a = [1,2,3];
a.forEach(function (value) {
  process._rawDebug(value);
  a.pop();
});

prints 1 2.

with a for (const hook of Array.from(active_hooks_array))

Array copy is too slow. When async_hooks is enabled this is the hottest code path we have.

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Ack. I was sure .forEach iterated over a fixed array (it just ignores newly added elements)

Expand All @@ -358,10 +353,11 @@ function emitHookFactory(symbol, name) {
}
} catch (e) {
fatalError(e);
} finally {
processing_hook -= 1;
}
processing_hook = false;

if (tmp_active_hooks_array !== null) {
if (processing_hook === 0 && tmp_active_hooks_array !== null) {
restoreTmpHooks();
}
};
Expand Down Expand Up @@ -427,7 +423,7 @@ function emitDestroyS(asyncId) {
// slim chance of the application remaining stable after handling one of these
// exceptions.
function init(asyncId, type, triggerAsyncId, resource) {
processing_hook = true;
processing_hook += 1;
// Use a single try/catch for all hook to avoid setting up one per iteration.
try {
for (var i = 0; i < active_hooks_array.length; i++) {
Expand All @@ -440,8 +436,20 @@ function init(asyncId, type, triggerAsyncId, resource) {
}
} catch (e) {
fatalError(e);
} finally {
processing_hook -= 1;
}

// * `tmp_active_hooks_array` is null if no hooks were added/removed while
// the hooks were running. In that case no restoration is needed.
// * In the case where another hook was added/removed while the hooks were
// running and a handle was created causing the `init` hooks to fire again,
// then `restoreTmpHooks` should not be called for the nested `hooks`.
// Otherwise `active_hooks_array` can change during execution of the
// `hooks`.
if (processing_hook === 0 && tmp_active_hooks_array !== null) {
restoreTmpHooks();
}
processing_hook = false;
}


Expand Down
23 changes: 23 additions & 0 deletions test/async-hooks/test-disable-in-init.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
'use strict';

const common = require('../common');
const async_hooks = require('async_hooks');
const fs = require('fs');

let nestedCall = false;

async_hooks.createHook({
init: common.mustCall(function(id, type) {
nestedHook.disable();
if (!nestedCall) {
nestedCall = true;
fs.access(__filename, common.mustCall());
}
}, 2)
}).enable();

const nestedHook = async_hooks.createHook({
init: common.mustCall(2)
}).enable();

fs.access(__filename, common.mustCall());
22 changes: 22 additions & 0 deletions test/async-hooks/test-enable-in-init.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
'use strict';

const common = require('../common');
const async_hooks = require('async_hooks');
const fs = require('fs');

const nestedHook = async_hooks.createHook({
init: common.mustNotCall()
});
let nestedCall = false;

async_hooks.createHook({
init: common.mustCall(function(id, type) {
nestedHook.enable();
if (!nestedCall) {
nestedCall = true;
fs.access(__filename, common.mustCall());
}
}, 2)
}).enable();

fs.access(__filename, common.mustCall());
19 changes: 19 additions & 0 deletions test/parallel/test-async-hooks-enable-recursive.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
'use strict';

const common = require('../common');
const async_hooks = require('async_hooks');
const fs = require('fs');

const nestedHook = async_hooks.createHook({
init: common.mustCall()
});

async_hooks.createHook({
init: common.mustCall((id, type) => {
nestedHook.enable();
}, 2)
}).enable();

fs.access(__filename, common.mustCall(() => {
fs.access(__filename, common.mustCall());
}));