Sparse IO implementation for memory-only cache

Implemented the following methods:
  MemEntryImpl::ReadSparseData
  MemEntryImpl::WriteSparseData
  MemEntryImpl::GetAvailableRange

TEST=DiskCacheEntryTest.Memory*

original CL: http://codereview.chromium.org/140049
Review URL: http://codereview.chromium.org/147217

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@19380 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 277 insertions, 33 deletions

diff --git a/net/disk_cache/mem_entry_impl.cc b/net/disk_cache/mem_entry_impl.cc
index 4905785..bf6359d 100644
--- a/net/disk_cache/mem_entry_impl.cc
+++ b/net/disk_cache/mem_entry_impl.cc
@@ -11,6 +11,28 @@
 
 using base::Time;
 
+namespace {
+
+const int kSparseData = 1;
+
+// Maximum size of a sparse entry is 2 to the power of this number.
+const int kMaxSparseEntryBits = 12;
+
+// Sparse entry has maximum size of 4KB.
+const int kMaxSparseEntrySize = 1 << kMaxSparseEntryBits;
+
+// Convert global offset to child index.
+inline int ToChildIndex(int64 offset) {
+  return static_cast<int>(offset >> kMaxSparseEntryBits);
+}
+
+// Convert global offset to offset in child entry.
+inline int ToChildOffset(int64 offset) {
+  return static_cast<int>(offset & (kMaxSparseEntrySize - 1));
+}
+
+}  // nemespace
+
 namespace disk_cache {
 
 MemEntryImpl::MemEntryImpl(MemBackendImpl* backend) {
@@ -18,6 +40,8 @@ MemEntryImpl::MemEntryImpl(MemBackendImpl* backend) {
   backend_ = backend;
   ref_count_ = 0;
   parent_ = NULL;
+  child_id_ = 0;
+  child_first_pos_ = 0;
   next_ = NULL;
   prev_ = NULL;
   for (int i = 0; i < NUM_STREAMS; i++)
@@ -34,25 +58,14 @@ bool MemEntryImpl::CreateEntry(const std::string& key) {
   key_ = key;
   last_modified_ = Time::Now();
   last_used_ = Time::Now();
-  type_ = kParentEntry;
   Open();
   backend_->ModifyStorageSize(0, static_cast<int32>(key.size()));
   return true;
 }
 
-bool MemEntryImpl::CreateChildEntry(MemEntryImpl* parent) {
-  parent_ = parent;
-  last_modified_ = Time::Now();
-  last_used_ = Time::Now();
-  type_ = kChildEntry;
-  // Insert this to the backend's ranking list.
-  backend_->InsertIntoRankingList(this);
-  return true;
-}
-
 void MemEntryImpl::Close() {
   // Only a parent entry can be closed.
-  DCHECK(type_ == kParentEntry);
+  DCHECK(type() == kParentEntry);
   ref_count_--;
   DCHECK(ref_count_ >= 0);
   if (!ref_count_ && doomed_)
@@ -61,14 +74,16 @@ void MemEntryImpl::Close() {
 
 void MemEntryImpl::Open() {
   // Only a parent entry can be opened.
-  DCHECK(type_ == kParentEntry);
+  // TODO(hclam): make sure it's correct to not apply the concept of ref
+  // counting to child entry.
+  DCHECK(type() == kParentEntry);
   ref_count_++;
   DCHECK(ref_count_ >= 0);
   DCHECK(!doomed_);
 }
 
 bool MemEntryImpl::InUse() {
-  if (type_ == kParentEntry) {
+  if (type() == kParentEntry) {
     return ref_count_ > 0;
   } else {
     // A child entry is always not in use. The consequence is that a child entry
@@ -81,11 +96,11 @@ bool MemEntryImpl::InUse() {
 void MemEntryImpl::Doom() {
   if (doomed_)
     return;
-  if (type_ == kParentEntry) {
+  if (type() == kParentEntry) {
     // Perform internal doom from the backend if this is a parent entry.
     backend_->InternalDoomEntry(this);
   } else {
-    // Manually detach from the parent entry and perform internal doom.
+    // Manually detach from the backend and perform internal doom.
     backend_->RemoveFromRankingList(this);
     InternalDoom();
   }
@@ -94,10 +109,23 @@ void MemEntryImpl::Doom() {
 void MemEntryImpl::InternalDoom() {
   doomed_ = true;
   if (!ref_count_) {
-    if (type_ == kParentEntry) {
-      // TODO(hclam): doom all child entries associated with this entry.
+    if (type() == kParentEntry) {
+      // If this is a parent entry, we need to doom all the child entries.
+      if (children_.get()) {
+        EntryMap children;
+        children.swap(*children_);
+        for (EntryMap::iterator i = children.begin();
+             i != children.end(); ++i) {
+          // Since a pointer to this object is also saved in the map, avoid
+          // dooming it.
+          if (i->second != this)
+            i->second->Doom();
+        }
+        DCHECK(children_->size() == 0);
+      }
     } else {
-      // TODO(hclam): detach this child entry from the parent entry.
+      // If this is a child entry, detach it from the parent.
+      parent_->DetachChild(child_id_);
     }
     delete this;
   }
@@ -105,7 +133,7 @@ void MemEntryImpl::InternalDoom() {
 
 std::string MemEntryImpl::GetKey() const {
   // A child entry doesn't have key so this method should not be called.
-  DCHECK(type_ == kParentEntry);
+  DCHECK(type() == kParentEntry);
   return key_;
 }
 
@@ -120,16 +148,12 @@ Time MemEntryImpl::GetLastModified() const {
 int32 MemEntryImpl::GetDataSize(int index) const {
   if (index < 0 || index >= NUM_STREAMS)
     return 0;
-
-  // TODO(hclam): handle the case when this is a parent entry and has associated
-  // child entries.
   return data_size_[index];
 }
 
 int MemEntryImpl::ReadData(int index, int offset, net::IOBuffer* buf,
     int buf_len, net::CompletionCallback* completion_callback) {
-  // This method can only be called with a parent entry.
-  DCHECK(type_ == kParentEntry);
+  DCHECK(type() == kParentEntry || index == kSparseData);
 
   if (index < 0 || index >= NUM_STREAMS)
     return net::ERR_INVALID_ARGUMENT;
@@ -152,8 +176,7 @@ int MemEntryImpl::ReadData(int index, int offset, net::IOBuffer* buf,
 
 int MemEntryImpl::WriteData(int index, int offset, net::IOBuffer* buf,
     int buf_len, net::CompletionCallback* completion_callback, bool truncate) {
-  // This method can only be called with a parent entry.
-  DCHECK(type_ == kParentEntry);
+  DCHECK(type() == kParentEntry || index == kSparseData);
 
   if (index < 0 || index >= NUM_STREAMS)
     return net::ERR_INVALID_ARGUMENT;
@@ -166,9 +189,6 @@ int MemEntryImpl::WriteData(int index, int offset, net::IOBuffer* buf,
   // offset of buf_len could be negative numbers.
   if (offset > max_file_size || buf_len > max_file_size ||
       offset + buf_len > max_file_size) {
-    int size = offset + buf_len;
-    if (size <= max_file_size)
-      size = kint32max;
     return net::ERR_FAILED;
   }
 
@@ -198,16 +218,160 @@ int MemEntryImpl::WriteData(int index, int offset, net::IOBuffer* buf,
 
 int MemEntryImpl::ReadSparseData(int64 offset, net::IOBuffer* buf, int buf_len,
                                  net::CompletionCallback* completion_callback) {
-  return net::ERR_CACHE_OPERATION_NOT_SUPPORTED;
+  DCHECK(type() == kParentEntry);
+
+  if (!InitSparseInfo())
+    return net::ERR_CACHE_OPERATION_NOT_SUPPORTED;
+
+  if (offset < 0 || buf_len < 0 || !buf_len)
+    return net::ERR_INVALID_ARGUMENT;
+
+  // We will keep using this buffer and adjust the offset in this buffer.
+  scoped_refptr<net::ReusedIOBuffer> io_buf = new net::ReusedIOBuffer(buf,
+                                                                      buf_len);
+
+  // Counts the number of bytes read.
+  int bytes_read = 0;
+
+  // Iterate until we have read enough.
+  while (bytes_read < buf_len) {
+    MemEntryImpl* child = OpenChild(offset + bytes_read, false);
+
+    // No child present for that offset.
+    if (!child)
+      break;
+
+    // We then need to prepare the child offset and len.
+    int child_offset = ToChildOffset(offset + bytes_read);
+
+    // If we are trying to read from a position that the child entry has no data
+    // we should stop.
+    if (child_offset < child->child_first_pos_)
+      break;
+    int ret = child->ReadData(kSparseData, child_offset, io_buf,
+                              buf_len - bytes_read, NULL);
+
+    // If we encounter an error in one entry, return immediately.
+    if (ret < 0)
+      return ret;
+    else if (ret == 0)
+      break;
+
+    // Increment the counter by number of bytes read in the child entry.
+    bytes_read += ret;
+    // And also adjust the buffer's offset.
+    if (bytes_read < buf_len)
+      io_buf->SetOffset(bytes_read);
+  }
+
+  UpdateRank(false);
+
+  return bytes_read;
 }
 
 int MemEntryImpl::WriteSparseData(int64 offset, net::IOBuffer* buf, int buf_len,
     net::CompletionCallback* completion_callback) {
-  return net::ERR_CACHE_OPERATION_NOT_SUPPORTED;
+  DCHECK(type() == kParentEntry);
+
+  if (!InitSparseInfo())
+    return net::ERR_CACHE_OPERATION_NOT_SUPPORTED;
+
+  if (offset < 0 || buf_len < 0)
+    return net::ERR_INVALID_ARGUMENT;
+
+  scoped_refptr<net::ReusedIOBuffer> io_buf = new net::ReusedIOBuffer(buf,
+                                                                      buf_len);
+  // Counter for amount of bytes written.
+  int bytes_written = 0;
+
+  // This loop walks through child entries continuously starting from |offset|
+  // and writes blocks of data (of maximum size kMaxSparseEntrySize) into each
+  // child entry until all |buf_len| bytes are written. The write operation can
+  // start in the middle of an entry.
+  while (bytes_written < buf_len) {
+    MemEntryImpl* child = OpenChild(offset + bytes_written, true);
+    int child_offset = ToChildOffset(offset + bytes_written);
+
+    // Find the right amount to write, this evaluates the remaining bytes to
+    // write and remaining capacity of this child entry.
+    int write_len = std::min(buf_len - bytes_written,
+                             kMaxSparseEntrySize - child_offset);
+
+    // Keep a record of the last byte position (exclusive) in the child.
+    int data_size = child->GetDataSize(kSparseData);
+
+    // Always writes to the child entry. This operation may overwrite data
+    // previously written.
+    // TODO(hclam): if there is data in the entry and this write is not
+    // continuous we may want to discard this write.
+    int ret = child->WriteData(kSparseData, child_offset, io_buf, write_len,
+                               NULL, true);
+    if (ret < 0)
+      return ret;
+    else if (ret == 0)
+      break;
+
+    // Keep a record of the first byte position in the child if the write was
+    // not aligned nor continuous. This is to enable witting to the middle
+    // of an entry and still keep track of data off the aligned edge.
+    if (data_size != child_offset)
+      child->child_first_pos_ = child_offset;
+
+    // Increment the counter.
+    bytes_written += ret;
+
+    // And adjust the offset in the IO buffer.
+    if (bytes_written < buf_len)
+      io_buf->SetOffset(bytes_written);
+  }
+
+  UpdateRank(true);
+
+  return bytes_written;
 }
 
 int MemEntryImpl::GetAvailableRange(int64 offset, int len, int64* start) {
-  return net::ERR_CACHE_OPERATION_NOT_SUPPORTED;
+  DCHECK(type() == kParentEntry);
+  DCHECK(start);
+
+  if (!InitSparseInfo())
+    return net::ERR_CACHE_OPERATION_NOT_SUPPORTED;
+
+  if (offset < 0 || len < 0 || !start)
+    return net::ERR_INVALID_ARGUMENT;
+
+  MemEntryImpl* current_child = NULL;
+
+  // Find the first child and record the number of empty bytes.
+  int empty = FindNextChild(offset, len, &current_child);
+  if (current_child) {
+    *start = offset + empty;
+    len -= empty;
+
+    // Counts the number of continuous bytes.
+    int continuous = 0;
+
+    // This loop scan for continuous bytes.
+    while (len && current_child) {
+      // Number of bytes available in this child.
+      int data_size = current_child->GetDataSize(kSparseData) -
+                      ToChildOffset(*start + continuous);
+      if (data_size > len)
+        data_size = len;
+
+      // We have found more continuous bytes so increment the count. Also
+      // decrement the length we should scan.
+      continuous += data_size;
+      len -= data_size;
+
+      // If the next child is discontinuous, break the loop.
+      if (FindNextChild(*start + continuous, len, &current_child))
+        break;
+    }
+    return continuous;
+  }
+  *start = offset;
+  return 0;
 }
 
 void MemEntryImpl::PrepareTarget(int index, int offset, int buf_len) {
@@ -238,4 +402,84 @@ void MemEntryImpl::UpdateRank(bool modified) {
     backend_->UpdateRank(this);
 }
 
+bool MemEntryImpl::InitSparseInfo() {
+  DCHECK(type() == kParentEntry);
+
+  if (!children_.get()) {
+    // If we already have some data in sparse stream but we are being
+    // initialized as a sparse entry, we should fail.
+    if (GetDataSize(kSparseData))
+      return false;
+    children_.reset(new EntryMap());
+
+    // The parent entry stores data for the first block, so save this object to
+    // index 0.
+    (*children_)[0] = this;
+  }
+  return true;
+}
+
+bool MemEntryImpl::InitChildEntry(MemEntryImpl* parent, int child_id) {
+  DCHECK(!parent_);
+  DCHECK(!child_id_);
+  parent_ = parent;
+  child_id_ = child_id;
+  last_modified_ = Time::Now();
+  last_used_ = Time::Now();
+  // Insert this to the backend's ranking list.
+  backend_->InsertIntoRankingList(this);
+  return true;
+}
+
+MemEntryImpl* MemEntryImpl::OpenChild(int64 offset, bool create) {
+  DCHECK(type() == kParentEntry);
+  int index = ToChildIndex(offset);
+  EntryMap::iterator i = children_->find(index);
+  if (i != children_->end()) {
+    return i->second;
+  } else if (create) {
+    MemEntryImpl* child = new MemEntryImpl(backend_);
+    child->InitChildEntry(this, index);
+    (*children_)[index] = child;
+    return child;
+  }
+  return NULL;
+}
+
+int MemEntryImpl::FindNextChild(int64 offset, int len, MemEntryImpl** child) {
+  DCHECK(child);
+  *child = NULL;
+  int scanned_len = 0;
+
+  // This loop tries to find the first existing child.
+  while (scanned_len < len) {
+    // This points to the current offset in the child.
+    int current_child_offset = ToChildOffset(offset + scanned_len);
+    MemEntryImpl* current_child = OpenChild(offset + scanned_len, false);
+    if (current_child) {
+      int child_first_pos = current_child->child_first_pos_;
+
+      // This points to the first byte that we should be reading from, we need
+      // to take care of the filled region and the current offset in the child.
+      int first_pos =  std::max(current_child_offset, child_first_pos);
+
+      // If the first byte position we should read from doesn't exceed the
+      // filled region, we have found the first child.
+      if (first_pos < current_child->GetDataSize(kSparseData)) {
+         *child = current_child;
+
+         // We need to advance the scanned length.
+         scanned_len += first_pos - current_child_offset;
+         break;
+      }
+    }
+    scanned_len += kMaxSparseEntrySize - current_child_offset;
+  }
+  return scanned_len;
+}
+
+void MemEntryImpl::DetachChild(int child_id) {
+  children_->erase(child_id);
+}
+
 }  // namespace disk_cache