Switch to sync default implementation of AsyncMultiRead.

include/rocksdb/file_system.h

@@ -673,8 +673,15 @@ class FileSystem : public Customizable {
  //
  // Default implementation is to return IOStatus::OK.
 
- virtual IOStatus Poll(std::vector<void*>& /*io_handles*/,
+ virtual IOStatus Poll(std::vector<void*>& io_handles,
  size_t /*min_completions*/) {
+ // RocksDB-Cloud contribution begin 
+ if (!io_handle.empty()) {
+ // Default implementations on async operations do not return any 
+ // io_handles. If you override them, you need to override Poll as well.
+ return IOStatus::NotSupported("Poll");
+ }
+ // RocksDB-Cloud contribution end 
  return IOStatus::OK();
  }
 
@@ -950,44 +957,21 @@ class FSRandomAccessFile {
  // request and result and status fields are output parameter set by underlying
  // FileSystem. The data should always be read into scratch field.
  //
- // Default implementation delegates to ReadAsync for each request.
+ // Default implementation is syncrhonous and delegates to MultiRead.
  virtual IOStatus MultiReadAsync(
  FSReadRequest* reqs, size_t num_reqs, const IOOptions& opts,
  std::function<void(const FSReadRequest*, size_t, void*)> cb, void* cb_arg,
- void** io_handles, size_t* num_io_handles, IOHandleDeleter* del_fns,
- IODebugContext* dbg) {
+ void** /*io_handles*/, size_t* num_io_handles, 
+ IOHandleDeleter* /*del_fns*/, IODebugContext* dbg) {
  assert(*num_io_handles == num_reqs);
  *num_io_handles = 0;
- // Counter that we use keep track of how many individual async reads are
- // still in progress.
- std::atomic<size_t> in_flight = 0;
- for (size_t idx = 0; idx < num_reqs; idx++) {
- auto& req = reqs[idx];
- auto local_cb = [&in_flight](const FSReadRequest&, void*) {
- // We are done with this read, decrement the counter and signal.
- in_flight--;
- in_flight.notify_one();
- };
- auto status = ReadAsync(req, opts, local_cb, nullptr, &io_handles[idx],
- &del_fns[idx], dbg);
- if (status != IOStatus::OK()) {
- // Delete in-progress IO-handles.
- for (size_t k = 0; k < *num_io_handles; k++) {
- if (io_handles[k] && del_fns[k]) {
- del_fns[k](io_handles[k]);
- io_handles[k] = nullptr;
- }
- }
- *num_io_handles = 0;
- return status;
- }
- (*num_io_handles)++;
- in_flight++;
- }
- for (auto cv = in_flight.load(); cv != 0;
- in_flight.wait(cv), cv = in_flight.load()) {
+
+ auto status = MultiRead(reqs, num_reqs, opts, dbg);
+ if (!status.ok()) {
+ return status;
  }
- // the operation is completed, call the 'op_cb'
+
+ // the operation has completed successfully, execute callbacks
  cb(reqs, num_reqs, cb_arg);
  return IOStatus::OK();
  }