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async_hooks: reduce code duplication by using a factory #13755

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async_hooks: reduce code duplication by using a factory #13755

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58f011f
async_hooks: reduce duplication with factory
BridgeAR Jun 18, 2017
4c00eee
async_hooks: add TODO entry
BridgeAR Jun 18, 2017
8a8117e
rename factory
BridgeAR Jun 21, 2017
8918fc8
address comment: use named functions
BridgeAR Jun 30, 2017
e4cd110
fixup func-style
BridgeAR Jul 3, 2017
795358a
fixup rename function
BridgeAR Jul 3, 2017
fc397f8
fixup add comment about naming fn
BridgeAR Jul 3, 2017
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83 changes: 24 additions & 59 deletions lib/async_hooks.js
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,9 @@ const init_symbol = Symbol('init');
const before_symbol = Symbol('before');
const after_symbol = Symbol('after');
const destroy_symbol = Symbol('destroy');
const emitBeforeN = hookFactory(before_symbol);
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nit: change this to hookFactoryEmit or emitHookFactory.

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@trevnorris PTAL...

const emitAfterN = hookFactory(after_symbol);
const emitDestroyN = hookFactory(destroy_symbol);

// Setup the callbacks that node::AsyncWrap will call when there are hooks to
// process. They use the same functions as the JS embedder API. These callbacks
Expand Down Expand Up @@ -325,8 +328,8 @@ function emitInitS(asyncId, type, triggerAsyncId, resource) {
triggerAsyncId = initTriggerId();
}

// I'd prefer allowing these checks to not exist, or only throw in a debug
// build, in order to improve performance.
// TODO(trevnorris): I'd prefer allowing these checks to not exist, or only
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good call changing this to a TODO.

// throw in a debug build, in order to improve performance.
if (!Number.isSafeInteger(asyncId) || asyncId < 0)
throw new RangeError('asyncId must be an unsigned integer');
if (typeof type !== 'string' || type.length <= 0)
Expand All @@ -342,24 +345,28 @@ function emitInitS(asyncId, type, triggerAsyncId, resource) {
}
}


function emitBeforeN(asyncId) {
processing_hook = true;
// 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++) {
if (typeof active_hooks_array[i][before_symbol] === 'function') {
active_hooks_array[i][before_symbol](asyncId);
function hookFactory(symbol) {
// Called from native. The asyncId stack handling is taken care of there
// before this is called.
return function(asyncId) {
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Have we verified how this'll change the stack trace from any of these? If V8 can properly infer the name based on the variable name then great.

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It does that on the newer v8 versions:

> const a = { foo: function () {}, bar() {}, baz: () => {} }
undefined
> a.foo.name
'foo'
> a.bar.name
'bar'
> a.baz.name
'baz'

But I am not certain if there might be a context in which it is not inferred. I am also not sure where to trigger a stack trace from one of these functions as I didn't look deep into the async_hooks code so far. Can you point me out to something or give me a small example?

I could enforce setting the name though.

function hookFactory(symbol, name) {
  const fn = function () {}
  Object.defineProperty(fn, 'name', {
    value: name
  })
  return fn
}

const hook = hookFactory(Symbol(), 'myName')

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The stack trace was changed so I now explicitly set the name and it's now looking good again.

Error
    at AsyncHook.before (repl:2:26)
    at emitBeforeN (async_hooks.js:358:40)
    at emitBeforeS (async_hooks.js:393:3)
    at nextTickEmitBefore (internal/process/next_tick.js:158:7)
    at process._tickDomainCallback (internal/process/next_tick.js:230:9)

processing_hook = true;
// 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++) {
if (typeof active_hooks_array[i][symbol] === 'function') {
active_hooks_array[i][symbol](asyncId);
}
}
} catch (e) {
fatalError(e);
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You asked how to reach this fatalError call. The following will do it:

require('async_hooks').createHook({
  before() { throw new Error('ah crud') },
}).enable();
setTimeout(() => {}, 10);

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Thx

}
} catch (e) {
fatalError(e);
}
processing_hook = false;
processing_hook = false;

if (tmp_active_hooks_array !== null) {
restoreTmpHooks();
}
if (tmp_active_hooks_array !== null) {
restoreTmpHooks();
}
};
}


Expand All @@ -383,28 +390,6 @@ function emitBeforeS(asyncId, triggerAsyncId = asyncId) {
}


// Called from native. The asyncId stack handling is taken care of there before
// this is called.
function emitAfterN(asyncId) {
processing_hook = true;
// 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++) {
if (typeof active_hooks_array[i][after_symbol] === 'function') {
active_hooks_array[i][after_symbol](asyncId);
}
}
} catch (e) {
fatalError(e);
}
processing_hook = false;

if (tmp_active_hooks_array !== null) {
restoreTmpHooks();
}
}


// TODO(trevnorris): Calling emitBefore/emitAfter from native can't adjust the
// kIdStackIndex. But what happens if the user doesn't have both before and
// after callbacks.
Expand All @@ -425,26 +410,6 @@ function emitDestroyS(asyncId) {
}


function emitDestroyN(asyncId) {
processing_hook = true;
// 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++) {
if (typeof active_hooks_array[i][destroy_symbol] === 'function') {
active_hooks_array[i][destroy_symbol](asyncId);
}
}
} catch (e) {
fatalError(e);
}
processing_hook = false;

if (tmp_active_hooks_array !== null) {
restoreTmpHooks();
}
}


// Emit callbacks for native calls. Since some state can be setup directly from
// C++ there's no need to perform all the work here.

Expand Down