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// Copyright (c) Meta Platforms, Inc. and affiliates.
//
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).#pragma once
#pragma once
#if USE_COROUTINES
#include "file/random_access_file_reader.h"
#include "folly/experimental/coro/ViaIfAsync.h"
#include "port/port.h"
#include "rocksdb/file_system.h"
#include "rocksdb/statistics.h"
#include "util/autovector.h"
#include "util/stop_watch.h"
namespace ROCKSDB_NAMESPACE {
class SingleThreadExecutor;
// AsyncFileReader implements the Awaitable concept, which allows calling
// coroutines to co_await it. When the AsyncFileReader Awaitable is
// resumed, it initiates the fie reads requested by the awaiting caller
// by calling RandomAccessFileReader's ReadAsync. It then suspends the
// awaiting coroutine. The suspended awaiter is later resumed by Wait().
class AsyncFileReader {
class ReadAwaiter;
template <typename Awaiter>
class ReadOperation;
public:
AsyncFileReader(FileSystem* fs, Statistics* stats) : fs_(fs), stats_(stats) {}
~AsyncFileReader() {}
ReadOperation<ReadAwaiter> MultiReadAsync(RandomAccessFileReader* file,
const IOOptions& opts,
FSReadRequest* read_reqs,
size_t num_reqs,
AlignedBuf* aligned_buf) noexcept {
return ReadOperation<ReadAwaiter>{*this, file, opts,
read_reqs, num_reqs, aligned_buf};
}
private:
friend SingleThreadExecutor;
// Implementation of the Awaitable concept
class ReadAwaiter {
public:
explicit ReadAwaiter(AsyncFileReader& reader, RandomAccessFileReader* file,
const IOOptions& opts, FSReadRequest* read_reqs,
size_t num_reqs, AlignedBuf* /*aligned_buf*/) noexcept
: reader_(reader),
file_(file),
opts_(opts),
read_reqs_(read_reqs),
num_reqs_(num_reqs),
next_(nullptr) {}
bool await_ready() noexcept { return false; }
// A return value of true means suspend the awaiter (calling coroutine). The
// awaiting_coro parameter is the handle of the awaiter. The handle can be
// resumed later, so we cache it here.
bool await_suspend(
folly::coro::impl::coroutine_handle<> awaiting_coro) noexcept {
awaiting_coro_ = awaiting_coro;
// MultiReadAsyncImpl always returns true, so caller will be suspended
return reader_.MultiReadAsyncImpl(this);
}
void await_resume() noexcept {}
private:
friend AsyncFileReader;
// The parameters passed to MultiReadAsync are cached here when the caller
// calls MultiReadAsync. Later, when the execution of this awaitable is
// started, these are used to do the actual IO
AsyncFileReader& reader_;
RandomAccessFileReader* file_;
const IOOptions& opts_;
FSReadRequest* read_reqs_;
size_t num_reqs_;
autovector<void*, 32> io_handle_;
autovector<IOHandleDeleter, 32> del_fn_;
folly::coro::impl::coroutine_handle<> awaiting_coro_;
// Use this to link to the next ReadAwaiter in the suspended coroutine
// list. The head and tail of the list are tracked by AsyncFileReader.
// We use this approach rather than an STL container in order to avoid
// extra memory allocations. The coroutine call already allocates a
// ReadAwaiter object.
ReadAwaiter* next_;
};
// An instance of ReadOperation is returned to the caller of MultiGetAsync.
// This represents an awaitable that can be started later.
template <typename Awaiter>
class ReadOperation {
public:
explicit ReadOperation(AsyncFileReader& reader,
RandomAccessFileReader* file, const IOOptions& opts,
FSReadRequest* read_reqs, size_t num_reqs,
AlignedBuf* aligned_buf) noexcept
: reader_(reader),
file_(file),
opts_(opts),
read_reqs_(read_reqs),
num_reqs_(num_reqs),
aligned_buf_(aligned_buf) {}
auto viaIfAsync(folly::Executor::KeepAlive<> executor) const {
return folly::coro::co_viaIfAsync(
std::move(executor),
Awaiter{reader_, file_, opts_, read_reqs_, num_reqs_, aligned_buf_});
}
private:
AsyncFileReader& reader_;
RandomAccessFileReader* file_;
const IOOptions& opts_;
FSReadRequest* read_reqs_;
size_t num_reqs_;
AlignedBuf* aligned_buf_;
};
// This function does the actual work when this awaitable starts execution
bool MultiReadAsyncImpl(ReadAwaiter* awaiter);
// Called by the SingleThreadExecutor to poll for async IO completion.
// This also resumes the awaiting coroutines.
void Wait();
// Head of the queue of awaiters waiting for async IO completion
ReadAwaiter* head_ = nullptr;
// Tail of the awaiter queue
ReadAwaiter* tail_ = nullptr;
// Total number of pending async IOs
size_t num_reqs_ = 0;
FileSystem* fs_;
Statistics* stats_;
};
} // namespace ROCKSDB_NAMESPACE
#endif // USE_COROUTINES
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