Fix shutdown hang (#16274)

jsteemann · KVS85 · web-flow · commit c578ba790c7e · 2022-05-16T14:25:29.000+03:00
* Fixed a potential hang on shutdown, when there were still document operations
  queued.

Co-authored-by: Vadim &lt;vadim@arangodb.com&gt;
diff --git a/CHANGELOG b/CHANGELOG
@@ -1,6 +1,9 @@
 v3.8.7 (XXXX-XX-XX)
 -------------------
 
+* Fixed a potential hang on shutdown, when there were still document operations
+  queued.
+
 * No good reason to fatal error in agency state, when local database entries
   lack local timestamp (legacy). In that situation, we will record epoch begin
   as local time.
diff --git a/arangod/VocBase/vocbase.cpp b/arangod/VocBase/vocbase.cpp
@@ -1737,9 +1737,16 @@ std::vector<std::shared_ptr<arangodb::LogicalView>> TRI_vocbase_t::views() {
 }
 
 void TRI_vocbase_t::processCollectionsOnShutdown(std::function<void(LogicalCollection*)> const& cb) {
-  RECURSIVE_WRITE_LOCKER(_dataSourceLock, _dataSourceLockWriteOwner);
+  std::vector<std::shared_ptr<arangodb::LogicalCollection>> collections;
+
+  // make a copy of _collections, so we can call the callback function without
+  // the lock
+  {
+    RECURSIVE_READ_LOCKER(_dataSourceLock, _dataSourceLockWriteOwner);
+    collections = _collections;
+  }
 
-  for (auto const& it : _collections) {
+  for (auto const& it : collections) {
     cb(it.get());
   }
 }

Original file line number	Diff line number	Diff line change
`@@ -1737,9 +1737,16 @@ std::vector<std::shared_ptr<arangodb::LogicalView>> TRI_vocbase_t::views() {`
`1737`	`1737`	`}`
`1738`	`1738`
`1739`	`1739`	`void TRI_vocbase_t::processCollectionsOnShutdown(std::function<void(LogicalCollection*)> const& cb) {`
`1740`		`- RECURSIVE_WRITE_LOCKER(_dataSourceLock, _dataSourceLockWriteOwner);`
	`1740`	`+ std::vector<std::shared_ptr<arangodb::LogicalCollection>> collections;`
	`1741`	`+`
	`1742`	`+ // make a copy of _collections, so we can call the callback function without`
	`1743`	`+ // the lock`
	`1744`	`+ {`
	`1745`	`+ RECURSIVE_READ_LOCKER(_dataSourceLock, _dataSourceLockWriteOwner);`
	`1746`	`+ collections = _collections;`
	`1747`	`+ }`
`1741`	`1748`
`1742`		`- for (auto const& it : _collections) {`
	`1749`	`+ for (auto const& it : collections) {`
`1743`	`1750`	`cb(it.get());`
`1744`	`1751`	`}`
`1745`	`1752`	`}`