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timer: call list.start regardless new or not #2830

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timer: call list.start regardless new or not #2830

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5 changes: 4 additions & 1 deletion lib/timers.js
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Original file line number Diff line number Diff line change
Expand Up @@ -40,14 +40,17 @@ exports.active = function(item) {
list = lists[msecs];
} else {
list = new Timer();
list.start(msecs, 0);

L.init(list);

lists[msecs] = list;
list.msecs = msecs;
list[kOnTimeout] = listOnTimeout;
}
// Call start regardless whether list is new
// or not to prevent incorrect active_handles
// count. See https://github.com/nodejs/node-v0.x-archive/issues/25831.
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This new logic is definitely not correct.

If you do this you are at very high risk (almost 100%) of delaying existing, running timers. Read my extensive comments in

node/lib/timers.js

Lines 68 to 78 in 7c9a691

// With this, virtually constant-time insertion (append), removal, and timeout
// is possible in the JavaScript layer. Any one list of timers is able to be
// sorted by just appending to it because all timers within share the same
// duration. Therefore, any timer added later will always have been scheduled to
// timeout later, thus only needing to be appended.
// Removal from an object-property linked list is also virtually constant-time
// as can be seen in the lib/internal/linkedlist.js implementation.
// Timeouts only need to process any timers due to currently timeout, which will
// always be at the beginning of the list for reasons stated above. Any timers
// after the first one encountered that does not yet need to timeout will also
// always be due to timeout at a later time.
on how this works if you don't believe me.

Perhaps it would work correctly if you did the following:

list.start(Timer.now() - list._idlePrev._idleStart, 0);

If that worked, I would be willing to entertain changing the impl to that.

(Note: made comment on a different line so it would show at the bottom of the issue thread.)

list.start(msecs, 0);
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What happens if the previous list start time was less than this list start time? I think it should check that, if I am following the logic correctly.

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cc @abbr ^


L.append(list, item);
assert(!L.isEmpty(list)); // list is not empty
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17 changes: 17 additions & 0 deletions test/addons/timers-active-handles/binding.cc
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@@ -0,0 +1,17 @@
#include <node.h>
#include <uv.h>

using namespace v8;
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Instead we prefer using v8::Local etc. for everything this test will use.


void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
int hCnt = uv_default_loop()->active_handles;
uv_run(uv_default_loop(), UV_RUN_ONCE);
args.GetReturnValue().Set(Integer::New(isolate, hCnt));
}

void init(Handle<Object> exports) {
NODE_SET_METHOD(exports, "run", Method);
}

NODE_MODULE(deasync, init)
8 changes: 8 additions & 0 deletions test/addons/timers-active-handles/binding.gyp
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@@ -0,0 +1,8 @@
{
'targets': [
{
'target_name': 'binding',
'sources': [ 'binding.cc' ]
}
]
}
13 changes: 13 additions & 0 deletions test/addons/timers-active-handles/test.js
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@@ -0,0 +1,13 @@
'use strict';

const assert = require('assert');
var uvRunOnce = require('./build/Release/binding');
setTimeout(function () {
var res;
setTimeout(function () {
res = true;
}, 2);
while (!res && uvRunOnce.run()) {
}
assert.equal(res, true);
}, 2);