#!/usr/bin/env python3 # Copyright 2023 gRPC authors. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. import sys from mako.template import Template seq_state = Template( """ <%def name="decl(promise_name, i, n)"> using Promise${i} = ${promise_name}; % if i < n-1: using NextFactory${i} = OncePromiseFactory; ${decl(f"typename NextFactory{i}::Promise", i+1, n)} % endif <%def name="state(i, n)"> % if i == 0: Promise0 current_promise; NextFactory0 next_factory; % elif i == n-1: union { struct { ${state(i-1, n)} } prior; Promise${i} current_promise; }; % else: union { struct { ${state(i-1, n)} } prior; P${i} current_promise; }; NextFactory${i} next_factory; % endif template class Traits, typename P, ${",".join(f"typename F{i}" for i in range(0,n-1))}> struct SeqState { <% name="PromiseLike

" %> % for i in range(0,n-1): using Promise${i} = ${name}; using PromiseResult${i} = typename Promise${i}::Result; using PromiseResultTraits${i} = Traits; using NextFactory${i} = OncePromiseFactory; <% name=f"typename NextFactory{i}::Promise" %>\\ % endfor using Promise${n-1} = ${name}; using PromiseResult${n-1} = typename Promise${n-1}::Result; using PromiseResultTraits${n-1} = Traits; using Result = typename PromiseResultTraits${n-1}::WrappedType; % if n == 1: Promise0 current_promise; % else: % for i in range(0,n-1): struct Running${i} { % if i != 0: union { GPR_NO_UNIQUE_ADDRESS Running${i-1} prior; % endif GPR_NO_UNIQUE_ADDRESS Promise${i} current_promise; % if i != 0: }; % endif GPR_NO_UNIQUE_ADDRESS NextFactory${i} next_factory; }; % endfor union { GPR_NO_UNIQUE_ADDRESS Running${n-2} prior; GPR_NO_UNIQUE_ADDRESS Promise${n-1} current_promise; }; % endif enum class State : uint8_t { ${",".join(f"kState{i}" for i in range(0,n))} }; GPR_NO_UNIQUE_ADDRESS State state = State::kState0; SeqState(P&& p, ${",".join(f"F{i}&& f{i}" for i in range(0,n-1))}) noexcept { Construct(&${"prior."*(n-1)}current_promise, std::forward

(p)); % for i in range(0,n-1): Construct(&${"prior."*(n-1-i)}next_factory, std::forward(f${i})); % endfor } ~SeqState() { switch (state) { % for i in range(0,n-1): case State::kState${i}: Destruct(&${"prior."*(n-1-i)}current_promise); goto tail${i}; % endfor case State::kState${n-1}: Destruct(¤t_promise); return; } % for i in range(0,n-1): tail${i}: Destruct(&${"prior."*(n-1-i)}next_factory); % endfor } SeqState(const SeqState& other) noexcept : state(other.state) { GPR_ASSERT(state == State::kState0); Construct(&${"prior."*(n-1-i)}current_promise, other.${"prior."*(n-1-i)}current_promise); % for i in range(0,n-1): Construct(&${"prior."*(n-1-i)}next_factory, other.${"prior."*(n-1-i)}next_factory); % endfor } SeqState& operator=(const SeqState& other) = delete; SeqState(SeqState&& other) noexcept : state(other.state) { switch (state) { % for i in range(0,n-1): case State::kState${i}: Construct(&${"prior."*(n-1-i)}current_promise, std::move(other.${"prior."*(n-1-i)}current_promise)); goto tail${i}; % endfor case State::kState${n-1}: Construct(¤t_promise, std::move(other.current_promise)); return; } % for i in range(0,n-1): tail${i}: Construct(&${"prior."*(n-1-i)}next_factory, std::move(other.${"prior."*(n-1-i)}next_factory)); % endfor } SeqState& operator=(SeqState&& other) = delete; Poll PollOnce() { switch (state) { % for i in range(0,n-1): case State::kState${i}: { auto result = ${"prior."*(n-1-i)}current_promise(); PromiseResult${i}* p = result.value_if_ready(); if (p == nullptr) return Pending{}; if (!PromiseResultTraits${i}::IsOk(*p)) { return PromiseResultTraits${i}::template ReturnValue(std::move(*p)); } Destruct(&${"prior."*(n-1-i)}current_promise); auto next_promise = PromiseResultTraits${i}::CallFactory(&${"prior."*(n-1-i)}next_factory, std::move(*p)); Destruct(&${"prior."*(n-1-i)}next_factory); Construct(&${"prior."*(n-2-i)}current_promise, std::move(next_promise)); state = State::kState${i+1}; } ABSL_FALLTHROUGH_INTENDED; % endfor default: case State::kState${n-1}: { auto result = current_promise(); auto* p = result.value_if_ready(); if (p == nullptr) return Pending{}; return Result(std::move(*p)); } } } };""" ) front_matter = """ #ifndef GRPC_SRC_CORE_LIB_PROMISE_DETAIL_SEQ_STATE_H #define GRPC_SRC_CORE_LIB_PROMISE_DETAIL_SEQ_STATE_H // This file is generated by tools/codegen/core/gen_seq.py #include #include #include #include "absl/base/attributes.h" #include #include "src/core/lib/gprpp/construct_destruct.h" #include "src/core/lib/promise/detail/promise_factory.h" #include "src/core/lib/promise/detail/promise_like.h" #include "src/core/lib/promise/poll.h" // A sequence under some traits for some set of callables P, Fs. // P should be a promise-like object that yields a value. // Fs... should be promise-factory-like objects that take the value from the // previous step and yield a promise. Note that most of the machinery in // PromiseFactory exists to make it possible for those promise-factory-like // objects to be anything that's convenient. // Traits defines how we move from one step to the next. Traits sets up the // wrapping and escape handling for the sequence. // Promises return wrapped values that the trait can inspect and unwrap before // passing them to the next element of the sequence. The trait can // also interpret a wrapped value as an escape value, which terminates // evaluation of the sequence immediately yielding a result. Traits for type T // have the members: // * type UnwrappedType - the type after removing wrapping from T (i.e. for // TrySeq, T=StatusOr yields UnwrappedType=U). // * type WrappedType - the type after adding wrapping if it doesn't already // exist (i.e. for TrySeq if T is not Status/StatusOr/void, then // WrappedType=StatusOr; if T is Status then WrappedType=Status (it's // already wrapped!)) // * template void CallFactory(Next* next_factory, T&& value) - // call promise factory next_factory with the result of unwrapping value, and // return the resulting promise. // * template Poll // CheckResultAndRunNext(T prior, RunNext run_next) - examine the value of // prior, and decide to escape or continue. If escaping, return the final // sequence value of type Poll. If continuing, return the value of // run_next(std::move(prior)). // // A state contains the current promise, and the promise factory to turn the // result of the current promise into the next state's promise. We play a shell // game such that the prior state and our current promise are kept in a union, // and the next promise factory is kept alongside in the state struct. // Recursively this guarantees that the next functions get initialized once, and // destroyed once, and don't need to be moved around in between, which avoids a // potential O(n**2) loop of next factory moves had we used a variant of states // here. The very first state does not have a prior state, and so that state has // a partial specialization below. The final state does not have a next state; // that state is inlined in BasicSeq since that was simpler to type. namespace grpc_core { namespace promise_detail { template class Traits, typename P, typename... Fs> struct SeqState; """ end_matter = """ } // namespace promise_detail } // namespace grpc_core #endif // GRPC_SRC_CORE_LIB_PROMISE_DETAIL_SEQ_STATE_H """ # utility: print a big comment block into a set of files def put_banner(files, banner): for f in files: for line in banner: print("// %s" % line, file=f) print("", file=f) with open(sys.argv[0]) as my_source: copyright = [] for line in my_source: if line[0] != "#": break for line in my_source: if line[0] == "#": copyright.append(line) break for line in my_source: if line[0] != "#": break copyright.append(line) copyright = [line[2:].rstrip() for line in copyright] with open("src/core/lib/promise/detail/seq_state.h", "w") as f: put_banner([f], copyright) print(front_matter, file=f) for n in range(2, 10): print(seq_state.render(n=n), file=f) print(end_matter, file=f)