X-Git-Url: https://git.cworth.org/git?a=blobdiff_plain;f=trace_snappyfile.cpp;h=ad0a57749a784ae7148ee056e4115c6f360980b2;hb=35c2793ac758997a0a1c2e558d384ab94754987d;hp=457f7e9529604d211ba86ce82e3900a4d80486af;hpb=b5f2ee344ef2914ca141608107c571ec0c28c6a6;p=apitrace

diff --git a/trace_snappyfile.cpp b/trace_snappyfile.cpp
index 457f7e9..ad0a577 100644
--- a/trace_snappyfile.cpp
+++ b/trace_snappyfile.cpp
@@ -1,3 +1,29 @@
+/**************************************************************************
+ *
+ * Copyright 2011 Zack Rusin
+ * All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ **************************************************************************/
+
+
 #include "trace_snappyfile.hpp"
 
 #include <snappy.h>
@@ -7,6 +33,32 @@
 
 using namespace Trace;
 
+/*
+ * Snappy file format.
+ * -------------------
+ *
+ * Snappy at its core is just a compressoin algorithm so we're
+ * creating a new file format which uses snappy compression
+ * to hold the trace data.
+ *
+ * The file is composed of a number of chunks, they are:
+ * chunk {
+ *     uint32 - specifying the length of the compressed data
+ *     compressed data
+ * }
+ * File can contain any number of such chunks.
+ * The default size of an uncompressed chunk is specified in
+ * SNAPPY_CHUNK_SIZE.
+ *
+ * Note:
+ * Currently the default size for a a to-be-compressed data is
+ * 1mb, meaning that the compressed data will be <= 1mb.
+ * The reason it's 1mb is because it seems
+ * to offer a pretty good compression/disk io speed ratio
+ * but that might change.
+ *
+ */
+
 SnappyFile::SnappyFile(const std::string &filename,
                               File::Mode mode)
     : File(),
@@ -83,16 +135,13 @@ bool SnappyFile::rawWrite(const void *buffer, int length)
 
 bool SnappyFile::rawRead(void *buffer, int length)
 {
-    if (m_stream.eof()) {
+    if (endOfData()) {
         return false;
     }
-    if (freeCacheSize() > length) {
-        memcpy(buffer, m_cachePtr, length);
-        m_cachePtr += length;
-    } else if (freeCacheSize() == length) {
+
+    if (freeCacheSize() >= length) {
         memcpy(buffer, m_cachePtr, length);
         m_cachePtr += length;
-        flushCache();
     } else {
         int sizeToRead = length;
         int offset = 0;
@@ -129,11 +178,9 @@ void SnappyFile::rawClose()
     m_cachePtr = NULL;
 }
 
-void SnappyFile::rawFlush(FlushType type)
+void SnappyFile::rawFlush()
 {
-    if (type == FlushDeep) {
-        flushCache();
-    }
+    flushCache();
     m_stream.flush();
 }
 
@@ -145,7 +192,7 @@ void SnappyFile::flushCache()
         ::snappy::RawCompress(m_cache, SNAPPY_CHUNK_SIZE - freeCacheSize(),
                               m_compressedCache, &compressedLength);
 
-        m_stream << compressedLength;
+        writeCompressedLength(compressedLength);
         m_stream.write(m_compressedCache, compressedLength);
         m_cachePtr = m_cache;
     } else if (m_mode == File::Read) {
@@ -153,8 +200,16 @@ void SnappyFile::flushCache()
             return;
         //assert(m_cachePtr == m_cache + m_cacheSize);
         size_t compressedLength;
-        m_stream >> compressedLength;
+        compressedLength = readCompressedLength();
         m_stream.read((char*)m_compressedCache, compressedLength);
+        /*
+         * The reason we peek here is because the last read will
+         * read all the way until the last character, but that will not
+         * trigger m_stream.eof() to be set, so by calling peek
+         * we assure that if we in fact have read the entire stream
+         * then the m_stream.eof() is always set.
+         */
+        m_stream.peek();
         ::snappy::GetUncompressedLength(m_compressedCache, compressedLength,
                                         &m_cacheSize);
         if (m_cache)
@@ -171,3 +226,15 @@ void SnappyFile::createCache(size_t size)
     m_cachePtr = m_cache;
     m_cacheSize = size;
 }
+
+void SnappyFile::writeCompressedLength(uint32_t value)
+{
+    m_stream.write((const char*)&value, sizeof value);
+}
+
+uint32_t SnappyFile::readCompressedLength()
+{
+    uint32_t len;
+    m_stream.read((char*)&len, sizeof len);
+    return len;
+}