VM top level vars are lost after a few iterations

[paleolitico]

We use a DSL to configure a system.
We load it with vm.
Sometimes, for debuging purposes, we use top level variables in the DSL,
that are read and modified by several functions.
After a few executions of these functions, modifications done by one function
is not seen by others.
Tested with iojs-1.1.0.
It doesn't happen with node-0.12.0.

The following code reproduces the bug in a simplified framework.

The DSL executor:

var vm = require('vm');
var fs = require('fs');

function include(script) {
  vm.runInContext(fs.readFileSync(script), ctxt, script);
}

var jobs = [];
function job(name, n, action) {
  jobs.push({name: name, times: n, action: action});
}

var sandbox = {
  console: console,
  job: job
};

var ctxt = vm.createContext(sandbox);

function load() {
  for (var i = 2; i < process.argv.length; i++) include(process.argv[i]);
}

function execute(jobs) {
  for (var i = 0; i < 2; i++) {
    for (var j = 0; j < jobs.length; j++) {
      var job = jobs[j];
      var times = job.times;
      var action = job.action;
      console.info("Executing " + job.name + " (" + times + ")");
      for (var k = 0; k < times; k++) {
        action();
      }
    }
  }
}

load();
execute(jobs);

A configuration script to give as argument

var n = 0;

job("Action 1", 1000, function() {
  n++;
});

job("Action 2", 1, function() {
  console.info("Action 2 output: " + n);
  n=0;
});

Executed with node-0.12.0 the result is as expected:

Executing Action 1 (1000)
Executing Action 2 (1)
Action 2 output: 1000
Executing Action 1 (1000)
Executing Action 2 (1)
Action 2 output: 1000

Executed with iojs-1.1.0 the result is

Executing Action 1 (1000)
Executing Action 2 (1)
Action 2 output: 517
Executing Action 1 (1000)
Executing Action 2 (1)
Action 2 output: 0

The value 517 differs on each execution.
I suppose it depends on the V8 optimization process.

Probably related to #548
and nodejs/node-v0.x-archive#9084

[Fishrock123]

cc @domenic

[Fishrock123]

@domenic also this?

[domenic]

Haven't been able to test this with the new patches, but I didn't see any reason why the new patches would necessarily fix it. I still have a list of vm bugs to work on :)

[jasnell]

is this still an issue?

[paleolitico]

It seems solved in current node releases, both LTS and Stable.
I have tested old versions and the last with the bug was iojs-2.5.0 (V8 4.2.77.21).
In iojs-3.0.0 (V8 4.4.63.26) was already solved.

Thank you very much.