[BlobAsync] Renderer support for blob file writing.

content/child/blob_storage/blob_consolidation.h

Index: content/child/blob_storage/blob_consolidation.h
diff --git a/content/child/blob_storage/blob_consolidation.h b/content/child/blob_storage/blob_consolidation.h
index 7c581d4cf95ba2e3dace669abd2f4fc58a52d6de..6053a2395a7098ff4c78c4bca579b3f934c50bc4 100644
--- a/content/child/blob_storage/blob_consolidation.h
+++ b/content/child/blob_storage/blob_consolidation.h
@@ -13,8 +13,10 @@
 #include <string>
 #include <vector>
 
+#include "base/callback_forward.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
 #include "storage/common/data_element.h"
 #include "third_party/WebKit/public/platform/WebThreadSafeData.h"
@@ -33,12 +35,14 @@ namespace content {
 //
 // NOTE: this class does not do memory accounting or garbage collecting. The
 // memory for the blob sticks around until this class is destructed.
-class CONTENT_EXPORT BlobConsolidation {
+class CONTENT_EXPORT BlobConsolidation
+    : public base::RefCountedThreadSafe<BlobConsolidation> {
  public:
   enum class ReadStatus {
     ERROR_UNKNOWN,
     ERROR_WRONG_TYPE,
     ERROR_OUT_OF_BOUNDS,
+    EARLY_ABORT,

[michaeln, 2016/04/21 01:58:41]

maybe call this CANCELLED_BY_VISITOR to make it clear it has to do with the
visitor returning false

[dmurph, 2016/04/22 22:37:09]

Done.

     OK
   };
   struct ConsolidatedItem {
@@ -64,7 +68,6 @@ class CONTENT_EXPORT BlobConsolidation {
   };
 
   BlobConsolidation();
-  ~BlobConsolidation();
 
   void AddDataItem(const blink::WebThreadSafeData& data);
   void AddFileItem(const base::FilePath& path,
@@ -91,19 +94,41 @@ class CONTENT_EXPORT BlobConsolidation {
 
   size_t total_memory() const { return total_memory_; }
 
-  // Reads memory from the given item into the given buffer. Returns:
+  // This method calls the |visibor| callback with the given memory item,

[michaeln, 2016/04/21 01:58:41]

spelling |visitor|

[dmurph, 2016/04/22 22:37:09]

Done.

+  // offset, and size. Since items are consolidated, |visitor| can be called
+  // multiple times, where the |total_memory_read| variable keeps track of how
+  // much memory the visitor has seen. The return value of |visitor| determines
+  // if we should continue reading memory, where 'false' triggers an early
+  // return and we return EARLY_ABORT. |visitor| is guaranteed to be called
+  // only during this method call.
+  // Returns:
   // * ReadStatus::ERROR if the state or arguments are invalid (see error log),
   // * ReadStatus::ERROR_WRONG_TYPE if the item at the index isn't memory,
   // * ReadStatus::ERROR_OUT_OF_BOUNDS if index, offset, or size are invalid,
-  // * ReadStatus::DONE if the memory has been successfully read.
+  // * ReadStatus::EARLY_ABORT if the visitor returns false before we're done,
+  // * ReadStatus::DONE if the memory has been successfully visited.
+  ReadStatus VisitMemory(
+      size_t consolidated_item_index,
+      size_t consolidated_offset,
+      size_t consolidated_size,
+      base::Callback<bool(size_t /* total_memory_read */,

[michaeln, 2016/04/21 01:58:41]

initially, i didn't understand the total_memory_read param. i don't think we
need this param since the callback can maintain state about progress if its
needed (if the sink was a file stream or a vector, we'd just append any data
received thru the callback)

[dmurph, 2016/04/22 22:37:09]

I end up using it in the places I use this method. Usually we're putting it into
a large memory block (either file or shared memory segment), so I'd rather keep
it in here. We keep track of it anyways in the loops, so I think it's cleaner to
do this instead of passing a stack pointer or something to the callback.

+                          const char* /* memory */,
+                          size_t /* memory_size */)> visitor) const;
+
+  // Reads memory from the given item into the given buffer. This is a simple
+  // wrapper of VisitMemory. Returns the same values as VisitMemory, except we
+  // don't return EARLY_ABORT.
   // Precondition: memory_out must be a valid pointer to memory with a size of
   //               at least consolidated_size.
   ReadStatus ReadMemory(size_t consolidated_item_index,
                         size_t consolidated_offset,
                         size_t consolidated_size,
-                        void* memory_out);
+                        void* memory_out) const;
 
  private:
+  friend class base::RefCountedThreadSafe<BlobConsolidation>;
+  ~BlobConsolidation();
+
   size_t total_memory_;
   std::set<std::string> referenced_blobs_;
   std::vector<ConsolidatedItem> consolidated_items_;