RCORE-2160 Make upload completion reporting multiprocess-compatible

CHANGELOG.md

@@ -9,6 +9,7 @@
 * Fixed a change of mode from Strong to All when removing links from an embedded object that links to a tombstone. This affects sync apps that use embedded objects which have a `Lst<Mixed>` that contains a link to another top level object which has been deleted by another sync client (creating a tombstone locally). In this particular case, the switch would cause any remaining link removals to recursively delete the destination object if there were no other links to it. ([#7828](https://github.com/realm/realm-core/issues/7828), since 14.0.0-beta.0)
 * Fixed removing backlinks from the wrong objects if the link came from a nested list, nested dictionary, top-level dictionary, or list of mixed, and the source table had more than 256 objects. This could manifest as `array_backlink.cpp:112: Assertion failed: int64_t(value >> 1) == key.value` when removing an object. ([#7594](https://github.com/realm/realm-core/issues/7594), since v11 for dictionaries)
 * Fixed the collapse/rejoin of clusters which contained nested collections with links. This could manifest as `array.cpp:319: Array::move() Assertion failed: begin <= end [2, 1]` when removing an object. ([#7839](https://github.com/realm/realm-core/issues/7839), since the introduction of nested collections in v14.0.0-beta.0)
+* wait_for_upload_completion() was inconsistent in how it handled commits which did not produce any changesets to upload. Previously it would sometimes complete immediately if all commits waiting to be uploaded were empty, and at other times it would wait for a server roundtrip. It will now always complete immediately. ([PR #7796](https://github.com/realm/realm-core/pull/7796)).
 
 ### Breaking changes
 * None.
@@ -20,6 +21,7 @@
 
 ### Internals
 * Fixed `Table::remove_object_recursive` which wouldn't recursively follow links through a single `Mixed` property. This feature is exposed publicly on `Table` but no SDK currently uses it, so this is considered internal. ([#7829](https://github.com/realm/realm-core/issues/7829), likely since the introduction of Mixed)
+* Upload completion is now tracked in a multiprocess-compatible manner ([PR #7796](https://github.com/realm/realm-core/pull/7796)).
 
 ----------------------------------------------
 

src/realm/chunked_binary.cpp

@@ -45,6 +45,13 @@ bool ChunkedBinaryData::is_null() const
     return chunk.is_null();
 }
 
+bool ChunkedBinaryData::empty() const
+{
+    BinaryIterator copy = m_begin;
+    BinaryData chunk = copy.get_next();
+    return chunk.size() == 0;
+}
+
 char ChunkedBinaryData::operator[](size_t index) const
 {
     BinaryIterator copy = m_begin;

src/realm/chunked_binary.hpp

@@ -54,6 +54,9 @@ class ChunkedBinaryData {
     /// the first chunk points to the nullptr.
     bool is_null() const;
 
+    /// Equivalent to `size() == 0`, but O(1) rather than O(N).
+    bool empty() const;
+
     /// FIXME: O(n)
     char operator[](size_t index) const;