support for single wasm interface #20
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include/eosio/vm/backend.hpp
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| @@ -130,6 +131,16 @@ namespace eosio { namespace vm { | |||
| construct(); | |||
| } | |||
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| backend& operator=(const backend& other) { | |||
| if (this != &other) { | |||
| mod = other.mod; | |||
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Where is this used. I'm not understanding the use of shared_ptr over unique_ptr and why we need a copy that shares module.
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It is used https://github.com/AntelopeIO/leap/blob/47e0372ab257534ae5e4133e3e3c6f894569125e/libraries/chain/webassembly/runtimes/eos-vm.cpp#L133. mod stores compiled information about a WASM; it is shared across multiple read-only threads when those threads happen to execute the same contract. The other fields exec_ctx_created_by_backend, initial_max_call_depth, and initial_max_pages are initial values of a backend (instantiated module). They are needed at the start of each execution.
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Personally I would prefer a clone() method, or maybe in this case share(). For such a complicated type using operator= in my opinion is too error prone.
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Thanks for your comments. I was struggling too initially on whether I should implement other constructors.
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| } | ||
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| void share(const backend& from) { | ||
| mod = from.mod; | ||
| exec_ctx_created_by_backend = from.exec_ctx_created_by_backend; |
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This doesn't seem right. Nothing is changing ctx here, so exec_ctx_created_by_backend shouldn't change either.
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Thank you Steve @swatanabe for reviewing this!
The "empty" backend's exec_ctx_created_by_backend is constructed to have the default value true (to support legacy uses). It needs to be set to the actual value from the instantiated module when used the first time.
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This means that share can only be used in a very specific way. Any other combination will result in leaks or double deletes. This is really dangerous to begin with and it's not even documented or checked.
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Thanks. I added checks to prevent invalid sharing and added comments about the method.
Change Description
A part of eosnetworkfoundation/product#149.
This is a support PR for the Leap PR that uses a single WASM interface per nodeos, not per thread. The main change in EOS VM is that compiled module
modis decoupled frombackendobject.API Changes
Documentation Additions