Speed up Snappy uncompression, new Logger interface.

- Removed one copy of an uncompressed block contents changing
  the signature of Snappy_Uncompress() so it uncompresses into a
  flat array instead of a std::string.
        
  Speeds up readrandom ~10%.

- Instead of a combination of Env/WritableFile, we now have a
  Logger interface that can be easily overridden applications
  that want to supply their own logging.

- Separated out the gcc and Sun Studio parts of atomic_pointer.h
  so we can use 'asm', 'volatile' keywords for Sun Studio.




git-svn-id: https://leveldb.googlecode.com/svn/trunk@39 62dab493-f737-651d-591e-8d6aee1b9529

table/format.cc

@@ -107,16 +107,20 @@ Status ReadBlock(RandomAccessFile* file,
       // Ok
       break;
     case kSnappyCompression: {
-      std::string decompressed;
-      if (!port::Snappy_Uncompress(data, n, &decompressed)) {
+      size_t ulength = 0;
+      if (!port::Snappy_GetUncompressedLength(data, n, &ulength)) {
         delete[] buf;
-        s = Status::Corruption("corrupted compressed block contents");
-        return s;
+        return Status::Corruption("corrupted compressed block contents");
       }
-      delete[] buf;     // Done with uncompressed data
-      buf = new char[decompressed.size()];
-      memcpy(buf, decompressed.data(), decompressed.size());
-      n = decompressed.size();
+      char* ubuf = new char[ulength];
+      if (!port::Snappy_Uncompress(data, n, ubuf)) {
+        delete[] buf;
+        delete[] ubuf;
+        return Status::Corruption("corrupted compressed block contents");
+      }
+      delete[] buf;
+      buf = ubuf;
+      n = ulength;
       break;
     }
     default: