add IsSyncThreadSafe() override to EncryptedWritableFile (#8993)

Summary:
EncryptedWritableFile is derived from FSWritableFile, which implements
the `IsSyncThreadSafe()` function as

    bool IsSyncThreadSafe() const { return false; }

EncryptedWritableFile does not override this method from the base class,
so the `IsSyncThreadSafe()` function on an EncryptedWritableFile will
always return false.
This change adds an override of `IsSyncThreadSafe()` to
EncryptedWritableFile so that the latter will now ask its underlying
`file_` object for the thread-safety of sync operations.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8993

Reviewed By: jay-zhuang

Differential Revision: D31613123

Pulled By: ajkr

fbshipit-source-id: b18625e21a9911744eef3215c29913490e4b6001

env/env_encryption.cc

@@ -255,12 +255,18 @@ IOStatus EncryptedWritableFile::PositionedAppend(const Slice& data,
   return file_->PositionedAppend(dataToAppend, offset, options, dbg);
 }
 
-  // Indicates the upper layers if the current WritableFile implementation
+// Indicates the upper layers if the current WritableFile implementation
-  // uses direct IO.
+// uses direct IO.
 bool EncryptedWritableFile::use_direct_io() const {
   return file_->use_direct_io();
 }
 
+// true if Sync() and Fsync() are safe to call concurrently with Append()
+// and Flush().
+bool EncryptedWritableFile::IsSyncThreadSafe() const {
+  return file_->IsSyncThreadSafe();
+}
+
   // Use the returned alignment value to allocate
   // aligned buffer for Direct I/O
 size_t EncryptedWritableFile::GetRequiredBufferAlignment() const {

include/rocksdb/env_encryption.h

@@ -318,6 +318,10 @@ class EncryptedWritableFile : public FSWritableFile {
                             const IOOptions& options,
                             IODebugContext* dbg) override;
 
+  // true if Sync() and Fsync() are safe to call concurrently with Append()
+  // and Flush().
+  bool IsSyncThreadSafe() const override;
+
   // Indicates the upper layers if the current WritableFile implementation
   // uses direct IO.
   bool use_direct_io() const override;