The companion Leap PR for using a single execution context per wasm interface

[linh2931]

The companion PR of EOS VM AntelopeIO/eos-vm#19 for using a single execution context per wasm interface.

Resolves #1456.

[spoonincode]

I was originally worried about the case where the apply options change between apply() calls right here.

For example reset_max_call_depth() sets the context's max call depth to initial_max_call_depth which was computed based on the options passed when the backend is created,
https://github.com/AntelopeIO/eos-vm/blob/8e1d571db99ff1eecd119c299b42886f72ef40b4/include/eosio/vm/backend.hpp#L177-L180
But the max call depth that should be configured at this point in time is what the current options protocol limits are.

But a few lines down from here,

leap/libraries/chain/webassembly/runtimes/eos-vm.cpp

Lines 141 to 147 in 295bb7c

	if(context.control.is_builtin_activated(builtin_protocol_feature_t::configurable_wasm_limits)) {
	const wasm_config& config = context.control.get_global_properties().wasm_configuration;
	opts = {config.max_pages, config.max_call_depth};
	}
	auto fn = [&]() {
	eosio::chain::webassembly::interface iface(context);
	_runtime->_bkend->initialize(&iface, opts);

The important part is the initialize() call that,
https://github.com/AntelopeIO/eos-vm/blob/8e1d571db99ff1eecd119c299b42886f72ef40b4/include/eosio/vm/backend.hpp#L198-L203
seems to set up the context correctly for each apply once WASM_LIMITS2 is activated.

[linh2931]

Thank you for your careful analysis.