From 4a6945983fa171fa843c6f8955ba601f733f3ca5 Mon Sep 17 00:00:00 2001
From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Sun, 24 Dec 2006 22:28:59 -0800
Subject: [PATCH] Add new interface for creating new segments.

---
 scandir.cc | 19 +++++++------------
 store.cc   | 43 ++++++++++++++++++++++++++++++++-----------
 store.h    | 25 +++++++++++++++++++++++--
 3 files changed, 62 insertions(+), 25 deletions(-)

diff --git a/scandir.cc b/scandir.cc
index 98285ac..d0ed67d 100644
--- a/scandir.cc
+++ b/scandir.cc
@@ -201,19 +201,12 @@ void scandir(const string& path)
 
 int main(int argc, char *argv[])
 {
-    struct uuid id = SegmentWriter::generate_uuid();
-    string filename = SegmentWriter::format_uuid(id);
-
-    printf("Backup UUID: %s\n", filename.c_str());
-    FILE *dump = fopen(filename.c_str(), "w");
-    if (dump == NULL) {
-        fprintf(stderr, "Cannot open file %s: %m\n", filename.c_str());
-        return 1;
-    }
+    SegmentStore ss(".");
+    SegmentWriter *sw = ss.new_segment();
+    info_dump = sw->new_object();
 
-    FileOutputStream os(dump);
-    SegmentWriter sw(os, id);
-    info_dump = sw.new_object();
+    string uuid = SegmentWriter::format_uuid(sw->get_uuid());
+    printf("Backup UUID: %s\n", uuid.c_str());
 
     try {
         scanfile(".");
@@ -221,5 +214,7 @@ int main(int argc, char *argv[])
         fprintf(stderr, "IOException: %s\n", e.getError().c_str());
     }
 
+    delete sw;
+
     return 0;
 }
diff --git a/store.cc b/store.cc
index 2dc6f84..1686798 100644
--- a/store.cc
+++ b/store.cc
@@ -166,15 +166,15 @@ string encode_u64(uint64_t val)
     return s.contents();
 }
 
-SegmentWriter::SegmentWriter(OutputStream &output, struct uuid u)
+SegmentWriter::SegmentWriter(OutputStream *output, struct uuid u)
     : out(output),
       id(u),
       object_stream(NULL)
 {
     /* Write out the segment header first. */
     static const char signature[] = "LBSSEG0\n";
-    out.write(signature, strlen(signature));
-    out.write(id.bytes, sizeof(struct uuid));
+    out->write(signature, strlen(signature));
+    out->write(id.bytes, sizeof(struct uuid));
 }
 
 SegmentWriter::~SegmentWriter()
@@ -185,18 +185,22 @@ SegmentWriter::~SegmentWriter()
     // Write out the object table which gives the sizes and locations of all
     // objects, and then add the trailing signature, which indicates the end of
     // the segment and gives the offset of the object table.
-    int64_t index_offset = out.get_pos();
+    int64_t index_offset = out->get_pos();
 
     for (object_table::const_iterator i = objects.begin();
          i != objects.end(); ++i) {
-        out.write_s64(i->first);
-        out.write_s64(i->second);
+        out->write_s64(i->first);
+        out->write_s64(i->second);
     }
 
     static const char signature2[] = "LBSEND";
-    out.write(signature2, strlen(signature2));
-    out.write_s64(index_offset);
-    out.write_u32(objects.size());
+    out->write(signature2, strlen(signature2));
+    out->write_s64(index_offset);
+    out->write_u32(objects.size());
+
+    /* The SegmentWriter takes ownership of the OutputStream it is writing to,
+     * and destroys it automatically when done with the segment. */
+    delete out;
 }
 
 OutputStream *SegmentWriter::new_object()
@@ -204,8 +208,8 @@ OutputStream *SegmentWriter::new_object()
     if (object_stream)
         finish_object();
 
-    object_start_offset = out.get_pos();
-    object_stream = new WrapperOutputStream(out);
+    object_start_offset = out->get_pos();
+    object_stream = new WrapperOutputStream(*out);
 
     return object_stream;
 }
@@ -240,3 +244,20 @@ string SegmentWriter::format_uuid(const struct uuid u)
 
     return string(buf);
 }
+
+SegmentStore::SegmentStore(const string &path)
+    : directory(path)
+{
+}
+
+SegmentWriter *SegmentStore::new_segment()
+{
+    struct uuid id = SegmentWriter::generate_uuid();
+    string filename = directory + "/" + SegmentWriter::format_uuid(id);
+
+    FILE *f = fopen(filename.c_str(), "wb");
+    if (f == NULL)
+        throw IOException("Unable to open new segment");
+
+    return new SegmentWriter(new FileOutputStream(f), id);
+}
diff --git a/store.h b/store.h
index 8344dda..0cd2c4b 100644
--- a/store.h
+++ b/store.h
@@ -122,9 +122,15 @@ struct uuid {
     uint8_t bytes[16];
 };
 
+/* A class which is used to pack multiple objects into a single segment, with a
+ * lookup table to quickly locate each object.  Call new_object() to get an
+ * OutputStream to which a new object may be written, and optionally
+ * finish_object() when finished writing the current object.  Only one object
+ * may be written to a segment at a time; if multiple objects must be written
+ * concurrently, they must be to different segments. */
 class SegmentWriter {
 public:
-    SegmentWriter(OutputStream &output, struct uuid u);
+    SegmentWriter(OutputStream *output, struct uuid u);
     ~SegmentWriter();
 
     struct uuid get_uuid() const { return id; }
@@ -140,7 +146,7 @@ public:
 private:
     typedef std::vector<std::pair<int64_t, int64_t> > object_table;
 
-    OutputStream &out;
+    OutputStream *out;
     struct uuid id;
 
     int64_t object_start_offset;
@@ -149,4 +155,19 @@ private:
     object_table objects;
 };
 
+/* A SegmentStore, as the name suggests, is used to store the contents of many
+ * segments.  The SegmentStore internally tracks where data should be placed
+ * (such as a local directory or remote storage), and allows new segments to be
+ * easily created as needed. */
+class SegmentStore {
+public:
+    // New segments will be stored in the given directory.
+    SegmentStore(const std::string &path);
+
+    SegmentWriter *new_segment();
+
+private:
+    std::string directory;
+};
+
 #endif // _LBS_STORE_H
-- 
2.20.1