Address review comments

db/table_cache.cc

@@ -42,13 +42,15 @@ static void DeleteEntry(const Slice& /*key*/, void* value) {
 }  // namespace ROCKSDB_NAMESPACE
 
 // Generate the regular and coroutine versions of some methods by
-// including table_cache_coro.h twice
+// including table_cache_sync_and_async.h twice
+// Macros in the header will expand differently based on whether
+// WITH_COROUTINES or WITHOUT_COROUTINES is defined
 // clang-format off
 #define WITHOUT_COROUTINES
-#include "db/table_cache_coro.h"
+#include "db/table_cache_sync_and_async.h"
 #undef WITHOUT_COROUTINES
 #define WITH_COROUTINES
-#include "db/table_cache_coro.h"
+#include "db/table_cache_sync_and_async.h"
 // clang-format on
 
 namespace ROCKSDB_NAMESPACE {

db/version_set.cc

@@ -72,13 +72,15 @@
 #include "util/user_comparator_wrapper.h"
 
 // Generate the regular and coroutine versions of some methods by
-// including version_set_coro.h twice
+// including version_set_sync_and_async.h twice
+// Macros in the header will expand differently based on whether
+// WITH_COROUTINES or WITHOUT_COROUTINES is defined
 // clang-format off
 #define WITHOUT_COROUTINES
-#include "db/version_set_coro.h"
+#include "db/version_set_sync_and_async.h"
 #undef WITHOUT_COROUTINES
 #define WITH_COROUTINES
-#include "db/version_set_coro.h"
+#include "db/version_set_sync_and_async.h"
 // clang-format on
 
 namespace ROCKSDB_NAMESPACE {

table/block_based/block_based_table_reader.cc

@@ -86,13 +86,15 @@ CacheAllocationPtr CopyBufferToHeap(MemoryAllocator* allocator, Slice& buf) {
 }  // namespace ROCKSDB_NAMESPACE
 
 // Generate the regular and coroutine versions of some methods by
-// including block_based_table_reader_coro.h twice
+// including block_based_table_reader_sync_and_async.h twice
+// Macros in the header will expand differently based on whether
+// WITH_COROUTINES or WITHOUT_COROUTINES is defined
 // clang-format off
 #define WITHOUT_COROUTINES
-#include "table/block_based/block_based_table_reader_coro.h"
+#include "table/block_based/block_based_table_reader_sync_and_async.h"
 #undef WITHOUT_COROUTINES
 #define WITH_COROUTINES
-#include "table/block_based/block_based_table_reader_coro.h"
+#include "table/block_based/block_based_table_reader_sync_and_async.h"
 // clang-format on
 
 namespace ROCKSDB_NAMESPACE {

util/async_file_reader.cc

@@ -36,7 +36,7 @@ bool AsyncFileReader::MultiReadAsyncImpl(ReadAwaiter* awaiter) {
   return true;
 }
 
-void AsyncFileReader::Poll() {
+void AsyncFileReader::Wait() {
   if (!head_) {
     return;
   }

util/async_file_reader.h

@@ -21,7 +21,7 @@ class SingleThreadExecutor;
 // 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 Poll().
+// awaiting coroutine. The suspended awaiter is later resumed by Wait().
 class AsyncFileReader {
   class ReadAwaiter;
   template <typename Awaiter>
@@ -84,6 +84,11 @@ class AsyncFileReader {
     autovector<void*, 32> io_handle_;
     autovector<IOHandleDeleter, 32> del_fn_;
     std::experimental::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_;
   };
 
@@ -123,7 +128,7 @@ class AsyncFileReader {
 
   // Called by the SingleThreadExecutor to poll for async IO completion.
   // This also resumes the awaiting coroutines.
-  void Poll();
+  void Wait();
 
   // Head of the queue of awaiters waiting for async IO completion
   ReadAwaiter* head_ = nullptr;

util/single_thread_executor.h

@@ -37,9 +37,9 @@ class SingleThreadExecutor : public folly::Executor {
         q.pop();
 
         if (q.empty()) {
-          // Prevent recursion, as the Poll may queue resumed coroutines
+          // Prevent recursion, as the Wait may queue resumed coroutines
           busy_ = true;
-          reader_.Poll();
+          reader_.Wait();
           busy_ = false;
         }
       }