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async_hooks: add executionAsyncResource
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Remove the need for the destroy hook in the basic APM case.

Co-authored-by: Stephen Belanger <admin@stephenbelanger.com>
PR-URL: nodejs#30959
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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2 people authored and addaleax committed Feb 11, 2020
1 parent 1c11ea4 commit 9fdb6e6
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151 changes: 151 additions & 0 deletions benchmark/async_hooks/async-resource-vs-destroy.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,151 @@
'use strict';

const { promisify } = require('util');
const { readFile } = require('fs');
const sleep = promisify(setTimeout);
const read = promisify(readFile);
const common = require('../common.js');
const {
createHook,
executionAsyncResource,
executionAsyncId
} = require('async_hooks');
const { createServer } = require('http');

// Configuration for the http server
// there is no need for parameters in this test
const connections = 500;
const path = '/';

const bench = common.createBenchmark(main, {
type: ['async-resource', 'destroy'],
asyncMethod: ['callbacks', 'async'],
n: [1e6]
});

function buildCurrentResource(getServe) {
const server = createServer(getServe(getCLS, setCLS));
const hook = createHook({ init });
const cls = Symbol('cls');
hook.enable();

return {
server,
close
};

function getCLS() {
const resource = executionAsyncResource();
if (resource === null || !resource[cls]) {
return null;
}
return resource[cls].state;
}

function setCLS(state) {
const resource = executionAsyncResource();
if (resource === null) {
return;
}
if (!resource[cls]) {
resource[cls] = { state };
} else {
resource[cls].state = state;
}
}

function init(asyncId, type, triggerAsyncId, resource) {
var cr = executionAsyncResource();
if (cr !== null) {
resource[cls] = cr[cls];
}
}

function close() {
hook.disable();
server.close();
}
}

function buildDestroy(getServe) {
const transactions = new Map();
const server = createServer(getServe(getCLS, setCLS));
const hook = createHook({ init, destroy });
hook.enable();

return {
server,
close
};

function getCLS() {
const asyncId = executionAsyncId();
return transactions.has(asyncId) ? transactions.get(asyncId) : null;
}

function setCLS(value) {
const asyncId = executionAsyncId();
transactions.set(asyncId, value);
}

function init(asyncId, type, triggerAsyncId, resource) {
transactions.set(asyncId, getCLS());
}

function destroy(asyncId) {
transactions.delete(asyncId);
}

function close() {
hook.disable();
server.close();
}
}

function getServeAwait(getCLS, setCLS) {
return async function serve(req, res) {
setCLS(Math.random());
await sleep(10);
await read(__filename);
res.setHeader('content-type', 'application/json');
res.end(JSON.stringify({ cls: getCLS() }));
};
}

function getServeCallbacks(getCLS, setCLS) {
return function serve(req, res) {
setCLS(Math.random());
setTimeout(() => {
readFile(__filename, () => {
res.setHeader('content-type', 'application/json');
res.end(JSON.stringify({ cls: getCLS() }));
});
}, 10);
};
}

const types = {
'async-resource': buildCurrentResource,
'destroy': buildDestroy
};

const asyncMethods = {
'callbacks': getServeCallbacks,
'async': getServeAwait
};

function main({ type, asyncMethod }) {
const { server, close } = types[type](asyncMethods[asyncMethod]);

server
.listen(common.PORT)
.on('listening', () => {

bench.http({
path,
connections
}, () => {
close();
});
});
}
56 changes: 56 additions & 0 deletions doc/api/async_hooks.md
Original file line number Diff line number Diff line change
Expand Up @@ -459,6 +459,62 @@ init for PROMISE with id 6, trigger id: 5 # the Promise returned by then()
after 6
```

#### `async_hooks.executionAsyncResource()`

<!-- YAML
added: REPLACEME
-->

* Returns: {Object} The resource representing the current execution.
Useful to store data within the resource.

Resource objects returned by `executionAsyncResource()` are most often internal
Node.js handle objects with undocumented APIs. Using any functions or properties
on the object is likely to crash your application and should be avoided.

Using `executionAsyncResource()` in the top-level execution context will
return an empty object as there is no handle or request object to use,
but having an object representing the top-level can be helpful.

```js
const { open } = require('fs');
const { executionAsyncId, executionAsyncResource } = require('async_hooks');

console.log(executionAsyncId(), executionAsyncResource()); // 1 {}
open(__filename, 'r', (err, fd) => {
console.log(executionAsyncId(), executionAsyncResource()); // 7 FSReqWrap
});
```

This can be used to implement continuation local storage without the
use of a tracking `Map` to store the metadata:

```js
const { createServer } = require('http');
const {
executionAsyncId,
executionAsyncResource,
createHook
} = require('async_hooks');
const sym = Symbol('state'); // Private symbol to avoid pollution

createHook({
init(asyncId, type, triggerAsyncId, resource) {
const cr = executionAsyncResource();
if (cr) {
resource[sym] = cr[sym];
}
}
}).enable();

const server = createServer(function(req, res) {
executionAsyncResource()[sym] = { state: req.url };
setTimeout(function() {
res.end(JSON.stringify(executionAsyncResource()[sym]));
}, 100);
}).listen(3000);
```

#### `async_hooks.executionAsyncId()`

<!-- YAML
Expand Down
4 changes: 3 additions & 1 deletion lib/async_hooks.js
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ const {
getHookArrays,
enableHooks,
disableHooks,
executionAsyncResource,
// Internal Embedder API
newAsyncId,
getDefaultTriggerAsyncId,
Expand Down Expand Up @@ -176,7 +177,7 @@ class AsyncResource {

runInAsyncScope(fn, thisArg, ...args) {
const asyncId = this[async_id_symbol];
emitBefore(asyncId, this[trigger_async_id_symbol]);
emitBefore(asyncId, this[trigger_async_id_symbol], this);

const ret = thisArg === undefined ?
fn(...args) :
Expand Down Expand Up @@ -211,6 +212,7 @@ module.exports = {
createHook,
executionAsyncId,
triggerAsyncId,
executionAsyncResource,
// Embedder API
AsyncResource,
};
45 changes: 33 additions & 12 deletions lib/internal/async_hooks.js
Original file line number Diff line number Diff line change
Expand Up @@ -28,18 +28,26 @@ const async_wrap = internalBinding('async_wrap');
* 3. executionAsyncId of the current resource.
*
* async_ids_stack is a Float64Array that contains part of the async ID
* stack. Each pushAsyncIds() call adds two doubles to it, and each
* popAsyncIds() call removes two doubles from it.
* stack. Each pushAsyncContext() call adds two doubles to it, and each
* popAsyncContext() call removes two doubles from it.
* It has a fixed size, so if that is exceeded, calls to the native
* side are used instead in pushAsyncIds() and popAsyncIds().
* side are used instead in pushAsyncContext() and popAsyncContext().
*/
const { async_hook_fields, async_id_fields, owner_symbol } = async_wrap;
const {
async_hook_fields,
async_id_fields,
execution_async_resources,
owner_symbol
} = async_wrap;
// Store the pair executionAsyncId and triggerAsyncId in a std::stack on
// Environment::AsyncHooks::async_ids_stack_ tracks the resource responsible for
// the current execution stack. This is unwound as each resource exits. In the
// case of a fatal exception this stack is emptied after calling each hook's
// after() callback.
const { pushAsyncIds: pushAsyncIds_, popAsyncIds: popAsyncIds_ } = async_wrap;
const {
pushAsyncContext: pushAsyncContext_,
popAsyncContext: popAsyncContext_
} = async_wrap;
// For performance reasons, only track Promises when a hook is enabled.
const { enablePromiseHook, disablePromiseHook } = async_wrap;
// Properties in active_hooks are used to keep track of the set of hooks being
Expand Down Expand Up @@ -92,6 +100,15 @@ const emitDestroyNative = emitHookFactory(destroy_symbol, 'emitDestroyNative');
const emitPromiseResolveNative =
emitHookFactory(promise_resolve_symbol, 'emitPromiseResolveNative');

const topLevelResource = {};

function executionAsyncResource() {
const index = async_hook_fields[kStackLength] - 1;
if (index === -1) return topLevelResource;
const resource = execution_async_resources[index];
return resource;
}

// Used to fatally abort the process if a callback throws.
function fatalError(e) {
if (typeof e.stack === 'string') {
Expand Down Expand Up @@ -330,8 +347,8 @@ function emitInitScript(asyncId, type, triggerAsyncId, resource) {
}


function emitBeforeScript(asyncId, triggerAsyncId) {
pushAsyncIds(asyncId, triggerAsyncId);
function emitBeforeScript(asyncId, triggerAsyncId, resource) {
pushAsyncContext(asyncId, triggerAsyncId, resource);

if (async_hook_fields[kBefore] > 0)
emitBeforeNative(asyncId);
Expand All @@ -342,7 +359,7 @@ function emitAfterScript(asyncId) {
if (async_hook_fields[kAfter] > 0)
emitAfterNative(asyncId);

popAsyncIds(asyncId);
popAsyncContext(asyncId);
}


Expand All @@ -360,6 +377,7 @@ function clearAsyncIdStack() {
async_id_fields[kExecutionAsyncId] = 0;
async_id_fields[kTriggerAsyncId] = 0;
async_hook_fields[kStackLength] = 0;
execution_async_resources.splice(0, execution_async_resources.length);
}


Expand All @@ -369,31 +387,33 @@ function hasAsyncIdStack() {


// This is the equivalent of the native push_async_ids() call.
function pushAsyncIds(asyncId, triggerAsyncId) {
function pushAsyncContext(asyncId, triggerAsyncId, resource) {
const offset = async_hook_fields[kStackLength];
if (offset * 2 >= async_wrap.async_ids_stack.length)
return pushAsyncIds_(asyncId, triggerAsyncId);
return pushAsyncContext_(asyncId, triggerAsyncId, resource);
async_wrap.async_ids_stack[offset * 2] = async_id_fields[kExecutionAsyncId];
async_wrap.async_ids_stack[offset * 2 + 1] = async_id_fields[kTriggerAsyncId];
execution_async_resources[offset] = resource;
async_hook_fields[kStackLength]++;
async_id_fields[kExecutionAsyncId] = asyncId;
async_id_fields[kTriggerAsyncId] = triggerAsyncId;
}


// This is the equivalent of the native pop_async_ids() call.
function popAsyncIds(asyncId) {
function popAsyncContext(asyncId) {
const stackLength = async_hook_fields[kStackLength];
if (stackLength === 0) return false;

if (enabledHooksExist() && async_id_fields[kExecutionAsyncId] !== asyncId) {
// Do the same thing as the native code (i.e. crash hard).
return popAsyncIds_(asyncId);
return popAsyncContext_(asyncId);
}

const offset = stackLength - 1;
async_id_fields[kExecutionAsyncId] = async_wrap.async_ids_stack[2 * offset];
async_id_fields[kTriggerAsyncId] = async_wrap.async_ids_stack[2 * offset + 1];
execution_async_resources.pop();
async_hook_fields[kStackLength] = offset;
return offset > 0;
}
Expand Down Expand Up @@ -426,6 +446,7 @@ module.exports = {
clearDefaultTriggerAsyncId,
clearAsyncIdStack,
hasAsyncIdStack,
executionAsyncResource,
// Internal Embedder API
newAsyncId,
getOrSetAsyncId,
Expand Down
2 changes: 1 addition & 1 deletion lib/internal/process/task_queues.js
Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,7 @@ function processTicksAndRejections() {
do {
while (tock = queue.shift()) {
const asyncId = tock[async_id_symbol];
emitBefore(asyncId, tock[trigger_async_id_symbol]);
emitBefore(asyncId, tock[trigger_async_id_symbol], tock);

try {
const callback = tock.callback;
Expand Down
6 changes: 3 additions & 3 deletions lib/internal/timers.js
Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,7 @@ const {
emitInit,
emitBefore,
emitAfter,
emitDestroy
emitDestroy,
} = require('internal/async_hooks');

// Symbols for storing async id state.
Expand Down Expand Up @@ -448,7 +448,7 @@ function getTimerCallbacks(runNextTicks) {
prevImmediate = immediate;

const asyncId = immediate[async_id_symbol];
emitBefore(asyncId, immediate[trigger_async_id_symbol]);
emitBefore(asyncId, immediate[trigger_async_id_symbol], immediate);

try {
const argv = immediate._argv;
Expand Down Expand Up @@ -537,7 +537,7 @@ function getTimerCallbacks(runNextTicks) {
continue;
}

emitBefore(asyncId, timer[trigger_async_id_symbol]);
emitBefore(asyncId, timer[trigger_async_id_symbol], timer);

let start;
if (timer._repeat)
Expand Down
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