[io] make buffering state explicit in RRawFile

Author: jblomer

io/io/inc/ROOT/RRawFile.hxx

@@ -47,12 +47,13 @@ public:
 
    /// On construction, an ROptions parameter can customize the RRawFile behavior
    struct ROptions {
+      static constexpr size_t kUseDefaultBlockSize = std::size_t(-1); ///< Use protocol-dependent default block size
+
       ELineBreaks fLineBreak = ELineBreaks::kAuto;
-      /// Read at least fBlockSize bytes at a time. A value of zero turns off I/O buffering. A negative value indicates
-      /// that the protocol-dependent default block size should be used.
+      /// Read at least fBlockSize bytes at a time. A value of zero turns off I/O buffering.
       /// After construction, a negative block size is used to store the block size value when buffering is turned off
       /// (see `SetBuffering()`).
-      int fBlockSize = -1;
+      size_t fBlockSize = kUseDefaultBlockSize;
       // Define an empty constructor to work around a bug in Clang: https://github.com/llvm/llvm-project/issues/36032
       ROptions() {}
    };
@@ -119,6 +120,8 @@ private:
    std::uint64_t fFileSize = kUnknownFileSize;
    /// Files are opened lazily and only when required; the open state is kept by this flag
    bool fIsOpen = false;
+   /// Runtime switch to decide if reads are buffered or directly sent to ReadAtImpl()
+   bool fIsBuffering = true;
 
 protected:
    std::string fUrl;
@@ -180,7 +183,7 @@ public:
    /// Turn off buffered reads; all scalar read requests go directly to the implementation. Buffering can be turned
    /// back on.
    void SetBuffering(bool value);
-   bool IsBuffering() const { return fOptions.fBlockSize > 0; }
+   bool IsBuffering() const { return fIsBuffering; }
 
    /// Read the next line starting from the current value of fFilePos. Returns false if the end of the file is reached.
    bool Readln(std::string &line);

io/io/src/RRawFile.cxx

@@ -151,11 +151,9 @@ size_t ROOT::Internal::RRawFile::ReadAt(void *buffer, size_t nbytes, std::uint64
       return 0;
 
    // "Large" reads are served directly, bypassing the cache; since nbytes > 0, fBlockSize == 0 is also handled here
-   if ((fOptions.fBlockSize < 0) || nbytes > static_cast<unsigned int>(fOptions.fBlockSize))
+   if (!fIsBuffering || nbytes > static_cast<unsigned int>(fOptions.fBlockSize))
       return ReadAtImpl(buffer, nbytes, offset);
 
-   R__ASSERT(fOptions.fBlockSize > 0);
-
    if (!fBufferSpace) {
       fBufferSpace.reset(new unsigned char[kNumBlockBuffers * fOptions.fBlockSize]);
       for (unsigned int i = 0; i < kNumBlockBuffers; ++i) {
@@ -201,16 +199,9 @@ void ROOT::Internal::RRawFile::ReadV(RIOVec *ioVec, unsigned int nReq)
 
 void ROOT::Internal::RRawFile::SetBuffering(bool value)
 {
-   if (value) {
-      if (fOptions.fBlockSize < 0) {
-         fOptions.fBlockSize = -fOptions.fBlockSize;
-      }
-   } else {
-      if (fOptions.fBlockSize > 0) {
-         fOptions.fBlockSize = -fOptions.fBlockSize;
-         fBufferSpace.reset();
-      }
-   }
+   fIsBuffering = value;
+   if (!fIsBuffering)
+      fBufferSpace.reset();
 }
 
 bool ROOT::Internal::RRawFile::Readln(std::string &line)

io/io/src/RRawFileUnix.cxx

@@ -72,7 +72,7 @@ void ROOT::Internal::RRawFileUnix::OpenImpl()
       throw std::runtime_error("Cannot open '" + fUrl + "', error: " + std::string(strerror(errno)));
    }
 
-   if (fOptions.fBlockSize >= 0)
+   if (fOptions.fBlockSize != ROptions::kUseDefaultBlockSize)
       return;
 
 #ifdef R__SEEK64

io/io/src/RRawFileWin.cxx

@@ -58,7 +58,7 @@ void ROOT::Internal::RRawFileWin::OpenImpl()
    // Prevent double buffering
    int res = setvbuf(fFilePtr, nullptr, _IONBF, 0);
    R__ASSERT(res == 0);
-   if (fOptions.fBlockSize < 0)
+   if (fOptions.fBlockSize == ROptions::kUseDefaultBlockSize)
       fOptions.fBlockSize = kDefaultBlockSize;
 }
 

net/davix/src/RRawFileDavix.cxx

@@ -75,7 +75,7 @@ void ROOT::Internal::RRawFileDavix::OpenImpl()
    if (fFileDes->fd == nullptr) {
       throw std::runtime_error("Cannot open '" + fUrl + "', error: " + err->getErrMsg());
    }
-   if (fOptions.fBlockSize < 0)
+   if (fOptions.fBlockSize == ROptions::kUseDefaultBlockSize)
       fOptions.fBlockSize = kDefaultBlockSize;
 }
 

net/netxng/src/RRawFileNetXNG.cxx

@@ -77,7 +77,8 @@ void ROOT::Internal::RRawFileNetXNG::OpenImpl()
    if( !st.IsOK() )
      throw std::runtime_error( "Cannot open '" + fUrl + "', " +
                                st.ToString() + "; " + st.GetErrorMessage() );
-   if( fOptions.fBlockSize < 0 ) fOptions.fBlockSize = kDefaultBlockSize;
+   if (fOptions.fBlockSize == ROptions::kUseDefaultBlockSize)
+      fOptions.fBlockSize = kDefaultBlockSize;
 }
 
 size_t ROOT::Internal::RRawFileNetXNG::ReadAtImpl(void *buffer, size_t nbytes, std::uint64_t offset)