[LLVMdev] [PATCH] Circular Buffered Debug Stream

[David Greene]

On Friday 18 December 2009 13:56, David Greene wrote:
> On Friday 18 December 2009 13:53, David Greene wrote:
> > > > +    void releaseStream() {
> > > > +      // Delete the stream if needed. Otherwise, transfer the buffer
> > > > +      // settings from this raw_ostream back to the underlying
> > > > stream. +      if (!TheStream)
> > > > +        return;
> > > > +      if (DeleteStream)
> > > > +        delete TheStream;
> > > > +      else if (BufferSize > 0)
> > > > +        TheStream->SetBufferSize(BufferSize);
> > > > +      else
> > > > +        TheStream->SetUnbuffered();
> > >
> > > Another issue is that this is transfering the circular stream's
> > > buffer to the underlying stream.  Would it make more sense and would it
> > > be worth it to save the underlying streams buffer size and restore it
> > > in releaseStream?
> >
> > Oh, I think this code is just wrong.  I'll rework it.
>
> No, it's right.  It's not transferring the buffer at all.  It's just
> setting the buffer size of the held stream when we release it.  This code
> is identical to the code in formatted_raw_ostream.

Here's the updated patch.

                                    -Dave

+    /// DELETE_STREAM - Tell the destructor to delete the held stream.
+    ///
+    static const bool DELETE_STREAM = true;
+
+    /// PRESERVE_STREAM - Tell the destructor to not delete the held
+    /// stream.
+    ///
+    static const bool PRESERVE_STREAM = false;
+
+  private:
+    /// TheStream - The real stream we output to. We set it to be
+    /// unbuffered, since we're already doing our own buffering.
+    ///
+    raw_ostream *TheStream;
+
+    /// DeleteStream - Do we need to delete TheStream in the
+    /// destructor?
+    ///
+    bool DeleteStream;
+
+    /// BufferSize - The size of the buffer in bytes.
+    ///
+    size_t BufferSize;
+
+    /// BufferArray - The actual buffer storage.
+    ///
+    char *BufferArray;
+
+    /// Cur - Pointer to the current output point in BufferArray.
+    ///
+    char *Cur;
+    
+    /// printLog - Dump the contents of the buffer to Stream.
+    ///
+    void printLog(void) {
+      TheStream->write(BufferArray, BufferSize);
+      Cur = BufferArray;
+    }
+
+    virtual void write_impl(const char *Ptr, size_t Size);
+
+    /// current_pos - Return the current position within the stream,
+    /// not counting the bytes currently in the buffer.
+    virtual uint64_t current_pos() { 
+      // This has the same effect as calling TheStream.current_pos(),
+      // but that interface is private.
+      return TheStream->tell() - TheStream->GetNumBytesInBuffer();
+    }
+
+  public:
+    /// circular_raw_ostream - Open the specified file for
+    /// writing. 
+    ///
+    /// As a side effect, if BuffSize is nonzero, the given Stream is
+    /// set to be Unbuffered.  This is because circular_raw_ostream
+    /// does its own buffering, so it doesn't want another layer of
+    /// buffering to be happening underneath it.
+    ///
+    circular_raw_ostream(raw_ostream &Stream, size_t BuffSize = 8192,
+                         bool Delete = false) 
+        : raw_ostream(/*unbuffered*/true),
+            TheStream(0),
+            DeleteStream(PRESERVE_STREAM),
+            BufferSize(BuffSize),
+            BufferArray(0) {
+      if (BufferSize > 0)
+        BufferArray = new char[BufferSize];
+      Cur = BufferArray;
+      setStream(Stream, Delete);
+    }
+    explicit circular_raw_ostream()
+        : raw_ostream(/*unbuffered*/true),
+            TheStream(0),
+            DeleteStream(PRESERVE_STREAM),
+            BufferArray(0) {
+      Cur = BufferArray;
+    }
+
+    ~circular_raw_ostream() {
+      flush();
+      dumpLog();
+      releaseStream();
+      delete[] BufferArray;
+    }
+
+    void setStream(raw_ostream &Stream, bool Delete = false) {
+      releaseStream();
+
+      TheStream = &Stream;
+      DeleteStream = Delete;
+
+      if (BufferSize > 0) {
+        // This circular_raw_ostream will do its own buffering and it
+        // doesn't need or want TheStream to do another layer of
+        // buffering underneath. Tell TheStream not to do its own
+        // buffering.
+        TheStream->SetUnbuffered();
+      }
+    }
+
+    /// dumpLog - Force output of the buffer along with a small
+    /// header.
+    ///
+    void dumpLog(void);
+
+  private:
+    void releaseStream() {
+      // Delete the stream if needed. Otherwise, transfer the buffer
+      // settings from this raw_ostream back to the underlying stream.
+      if (!TheStream)
+        return;
+      if (DeleteStream)
+        delete TheStream;
+      else if (BufferSize > 0)
+        TheStream->SetBufferSize(BufferSize);
+      else
+        TheStream->SetUnbuffered();
+    }
+  };
+} // end llvm namespace
+
+
+#endif
Index: lib/Support/circular_raw_ostream.cpp
===================================================================
--- lib/Support/circular_raw_ostream.cpp	(revision 0)
+++ lib/Support/circular_raw_ostream.cpp	(revision 0)
@@ -0,0 +1,46 @@
+//===- circulat_raw_ostream.cpp - Implement the circular_raw_ostream class 
-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This implements support for circular buffered streams.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/circular_raw_ostream.h"
+
+#include <algorithm>
+
+using namespace llvm;
+
+void circular_raw_ostream::write_impl(const char *Ptr, size_t Size) {
+  if (BufferSize > 0) {
+    // Write into the buffer, wrapping if necessary.
+    while (Size > 0) {
+      unsigned Bytes = std::min(Size, BufferSize);
+      memcpy(Cur, Ptr, Bytes);
+      Size -= Bytes;
+      if (Cur == BufferArray + BufferSize)
+        // Reset the output pointer to the start of the buffer.
+        Cur = BufferArray;
+    }    
+  }
+  else {
+    TheStream->write(Ptr, Size);
+  }
+}
+
+void circular_raw_ostream::dumpLog(void) {
+  if (BufferSize > 0) {
+    // Write out the buffer
+    const char *msg = "*** Log Output ***\n";
+    int num = std::strlen(msg);
+ 
+    TheStream->write(msg, num);
+    printLog();
+  }
+}