Add circular_raw_ostream, which buffers its output in a circular queue

and outputs it when explicitly flushed.  The intent is to use it in
situations such as debug output logging where a signal handler can take
care of flushing the buffer at program termination.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92001 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/circular_raw_ostream.cpp

@@ -0,0 +1,47 @@
+//===- 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) {
+    TheStream->write(Ptr, Size);
+    return;
+  }
+
+  // Write into the buffer, wrapping if necessary.
+  while (Size != 0) {
+    unsigned Bytes = std::min(Size, BufferSize - (Cur - BufferArray));
+    memcpy(Cur, Ptr, Bytes);
+    Size -= Bytes;
+    Cur += Bytes;
+    if (Cur == BufferArray + BufferSize) {
+      // Reset the output pointer to the start of the buffer.
+      Cur = BufferArray;
+      Filled = true;
+    }
+  }    
+}
+
+void circular_raw_ostream::flushBufferWithBanner(void) {
+  if (BufferSize != 0) {
+    // Write out the buffer
+    int num = std::strlen(Banner); 
+    TheStream->write(Banner, num);
+    flushBuffer();
+  }
+}