search

jerryscript-project / jerryscript

Ultra-lightweight JavaScript engine for the Internet of Things.
https://jerryscript.net
Apache License 2.0
6.95k stars 672 forks source link

Support multiple instances of the VM within a process #1415

Closed DemiMarie closed 7 years ago

DemiMarie commented 8 years ago

Lua supports multiple lua_State instances within a process, each of which represents an entire Lua VM. Different lua_States can be run on different threads simultaneously. This is much better than Jerryscript's use of global variables.

This is a breaking change to the C API.

zherczeg commented 8 years ago

JerryScript has a generic approach for contexts, so you can use any model including a lua like model. It can be adopted to any environments with different computation power and memory capabilities. For example passing around a context pointer is too much work (overhead) for a 80MHz CPU, but no problem for a 1GHz CPU.

zherczeg commented 7 years ago

Closing due to inactivity. Please reopen if needed.

sebadoom commented 7 years ago

I think this is sorely needed. The current approach is very limited. I can't imagine why passing a single pointer to every JerryScript call (like Lua or other interpreters do) creates additional overhead. Is it due to register pressure?

zherczeg commented 7 years ago

In JerryScript we allow multiple instance models and users can add more if needed. For example JERRY_ENABLE_EXTERNAL_CONTEXT is one way to use multiple VMs.

sebadoom commented 7 years ago

I'm having a hard time understanding how that works. How do you switch contexts? Is this added complexity really necessary? What gains are specifically enabled by it?

sebadoom commented 7 years ago

OK, so after looking a bit more in detail this works by defining jerry_port_get_current_instance(). This would introduce the problem of locking when working with two threads, or even when switching contexts by mistake while inside a native function handler. So I ask again: what is the limitation that this scheme resolves? Is passing an additional pointer in each call problematic in any platform?

martijnthe commented 7 years ago

@sebadoom When using multiple threads, the idea is to implement jerry_port_get_current_instance() using the thread-local-storage API that your platform/OS/RTOS provides. This should be very straightforward. What platform/OS/... are you using?