Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 144 insertions, 0 deletions

diff --git a/src/rocksdb/util/async_file_reader.h b/src/rocksdb/util/async_file_reader.h
new file mode 100644
index 000000000..df69a840e
--- /dev/null
+++ b/src/rocksdb/util/async_file_reader.h
@@ -0,0 +1,144 @@
+//  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