* Added basic async capabilities for vm2.
This is a whole new Git branch, not the same one as last time
(https://github.com/status-im/nimbus-eth1/pull/1250) - there wasn't
much worth salvaging. Main differences:
I didn't do the "each opcode has to specify an async handler" junk
that I put in last time. Instead, in oph_memory.nim you can see
sloadOp calling asyncChainTo and passing in an async operation.
That async operation is then run by the execCallOrCreate (or
asyncExecCallOrCreate) code in interpreter_dispatch.nim.
In the test code, the (previously existing) macro called "assembler"
now allows you to add a section called "initialStorage", specifying
fake data to be used by the EVM computation run by that test. (In
the long run we'll obviously want to write tests that for-real use
the JSON-RPC API to asynchronously fetch data; for now, this was
just an expedient way to write a basic unit test that exercises the
async-EVM code pathway.)
There's also a new macro called "concurrentAssemblers" that allows
you to write a test that runs multiple assemblers concurrently (and
then waits for them all to finish). There's one example test using
this, in test_op_memory_lazy.nim, though you can't actually see it
doing so unless you uncomment some echo statements in
async_operations.nim (in which case you can see the two concurrently
running EVM computations each printing out what they're doing, and
you'll see that they interleave).
A question: is it possible to make EVMC work asynchronously? (For
now, this code compiles and "make test" passes even if ENABLE_EVMC
is turned on, but it doesn't actually work asynchronously, it just
falls back on doing the usual synchronous EVMC thing. See
FIXME-asyncAndEvmc.)
* Moved the AsyncOperationFactory to the BaseVMState object.
* Made the AsyncOperationFactory into a table of fn pointers.
Also ditched the plain-data Vm2AsyncOperation type; it wasn't
really serving much purpose. Instead, the pendingAsyncOperation
field directly contains the Future.
* Removed the hasStorage idea.
It's not the right solution to the "how do we know whether we
still need to fetch the storage value or not?" problem. I
haven't implemented the right solution yet, but at least
we're better off not putting in a wrong one.
* Added/modified/removed some comments.
(Based on feedback on the PR.)
* Removed the waitFor from execCallOrCreate.
There was some back-and-forth in the PR regarding whether nested
waitFor calls are acceptable:
https://github.com/status-im/nimbus-eth1/pull/1260#discussion_r998587449
The eventual decision was to just change the waitFor to a doAssert
(since we probably won't want this extra functionality when running
synchronously anyway) to make sure that the Future is already
finished.
why:
the v2 prefix of the file name was used as a visual aid when
comparing vm2 against vm sources
details:
all renamed v2*.nim sources compile locally with the -d:kludge:1 flag
set or without (some work with either)
only sources not renamed yet: v2state_transactions.nim
why:
using function stubs made it possible to check the syntax of an op
handler source file by compiling this very file. this was previously
impossible due cyclic import/include mechanism.
details:
only oph_call.nim, oph_create.nim and subsequently op_handlers.nim
still need the -d:kludge:1 flag for syntax check compiling. this flag
also works with interpreter_dispatch.nim which imports op_handlers.nim.
why:
step towards breaking circular dependency
details:
some functions from v2computation.nim have been extracted into
compu_helper.nim which does not explicitly back-import
v2computation.nim. all non recursive op handlers now import this source
file rather than v2computation.nim.
recursive call/create op handler still need to import v2computation.nim.
the executeOpcodes() function from interpreter_dispatch.nim has been
moved to v2computation.nim which allows for <import> rather than
<include> the interpreter_dispatch.nim source.
why:
this allows for passing back information which can eventually be
used for reducing use of exceptions
caveat:
call/create currently needs to un-capture the call-by-reference
(wrapper) argument using the Computation reference inside
why:
the previous approach was replacing the function-lets in
opcode_impl.nim by the particulate table handlers. the test
functions will verify the the handler functions are sort of
correct but not the assignments in the fork tables.
the handler names of old and new for tables are checked here.
caveat:
verifying tables currently takes a while at compile time.
