Dart VM isolates take about 35 MB of memory each

[whesse]

Each isolate that is created seems to take about 35 MB of memory until it is closed and GCd. This affects the number of asynchronous file system or socket operations that can be created, since they are implemented with isolates (currently). This also means that no system with more than a couple hundred isolates can work.

This seems to be true on both the debug and release ia32 builds. The following code shows the resulting memory use. If port.close() is called, then the isolates are GCd and memory use stays below 100 MB.

class A extends Isolate {
  A() : super.light(); // or heavy, makes no difference.
  void main() { /* port.close();*/ }
}

main() {
  var a = new A();
  for (var j = 0; j < 100; ++j ) {
    a.spawn();
    print(j);
  }
}

[iposva-google]

We are changing the rules for how Isolates are being recycled: If you do not register a handler on a port, then isolates cannot observe external input and thus can be closed down once the currently executing handler finishes. This will fix the above "broken" code. Todd, please assign back to me when this is in.

We are in the process of reducing the amount of memory that is needed to start a new isolate. Regardless of the progress we make there, I don't think you can rely on isolates for asynchronous operations for file access. As far as I know socket operations already are handled in a different manner.

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Set owner to @turnidge.
Added Accepted label.

[turnidge]

We decided not to change the rules for registering a null handler.

Right now we create the ReceivePort eagerly for a new isolate and store it in the new Isolate object. If we switched this to create the port on first access, then this would "fix" the leak when not closing the port. What do you think, Ivan?

[sigmundch]

Added Isolates label.

[turnidge]

Ivan -- how do you want to proceed on this bug? The reason it was originally assigned to me is no longer valid.

Since I'm not doing any work to reduce isolate size, we should close it or reassign it to somebody else.

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Set owner to @iposva-google.

[iposva-google]

The original reason for filing this bug has long gone: We now support native isolates to implement the IO libraries.

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Added AssumedStale label.