MMTk Options

[qinsoon]

In GitLab by @qinsoon on Jan 30, 2020, 14:03

Currently MMTk is initialized with a set of default options. Options are mutable and the VM can use process(name, value) to send options to MMTk.

According to our discussion, these are clear:

• For command line arguments (such as -X:gc), MMTk expects the VM to send them as a string at initialization. And those are immutable.
• MMTk also allows mutable options. VM can call certain APIs to set some options during execution, these options may change MMTk's behaviours.

For mutable options, as we are supposed to have multiple readers but one writer to the options, we could consider using lock-free data structures, such as https://github.com/jonhoo/rust-evmap.

[qinsoon]

In GitLab by @qinsoon on Jan 30, 2020, 14:15

changed the description

[qinsoon]

In GitLab by @qinsoon on Jan 30, 2020, 17:41

mentioned in merge request !23

[qinsoon]

Options include plan selection, which means we need to create an MMTk instance after parsing MMTk options. This makes the MMTk instance no longer static (at the moment, all bindings create MMTk instance statically with plan selection through env vars). So besides the work of refactoring MMTk options, we have to:

• refactor bindings so MMTk instances are not static variables (we could possibly use a pointer).
• refactor mmtk-core so we no longer assume MMTK is always static.

[qinsoon]

It is possible that we still allow using env vars for plan selection, but change other options so they can be initialised in bulk lazily.

[qinsoon]

Now MMTk provides APIs to set options. And both JikesRVM and OpenJDK support using command line options to set MMTk options. However, some options that are used at MMTk instantiation cannot be set through command line (we still have to use env vars for them). See #541.