store wasm globals in execution context such that a single parsed module can be shared by multiple threads

[linh2931]

Resolves #7.
A part of eosnetworkfoundation/product#149.

Currently globals are stored in a compiled module. This prevents the module from being shared by multiple execution threads, as multiple threads can modify the same global. To enable the same compiled module to be shared,
globals are moved out of module and into the execution context.

This opens possibilities for further parallelism and memory reduction for cached instantiated modules.

Change Description

API Changes

• API Changes

Documentation Additions

• Documentation Additions

[heifner]

Is there a reason for using get_global_* and set_global_* instead of just _globals[globalidx].value ?

[linh2931]

Is there a reason for using get_global_* and set_global_* instead of just _globals[globalidx].value ?

At the time when emit_get_global and emit_set_global are called, execution_conetxt is not constructed yet; we don't have access to _globals. We also want to decouple the generated instructions from physical address of execution_context.