Reapply "SERVER-18277 Clarify locking of Client when accessing its stored OperationContext."

This reverts commit 993fc5e4ed9264965f16a948d3732d3fc55d1255.

1 files changed, 21 insertions, 3 deletions

diff --git a/src/mongo/db/client.h b/src/mongo/db/client.h
index 63750b69523..597ed07dd70 100644
--- a/src/mongo/db/client.h
+++ b/src/mongo/db/client.h
@@ -86,11 +86,29 @@ namespace mongo {
         void lock() { _lock.lock(); }
         void unlock() { _lock.unlock(); }
 
-        // Changes the currently active operation context on this client. There can only be one
-        // active OperationContext at a time.
+        /**
+         * Sets the active operation context on this client to "txn", which must be non-NULL.
+         *
+         * It is an error to call this method if there is already an operation context on Client.
+         * It is an error to call this on an unlocked client.
+         */
         void setOperationContext(OperationContext* txn);
+
+        /**
+         * Clears the active operation context on this client.
+         *
+         * There must already be such a context set on this client.
+         * It is an error to call this on an unlocked client.
+         */
         void resetOperationContext();
-        const OperationContext* getOperationContext() const { return _txn; }
+
+        /**
+         * Gets the operation context active on this client, or nullptr if there is no such context.
+         *
+         * It is an error to call this method on an unlocked client, or to use the value returned
+         * by this method while the client is not locked.
+         */
+        OperationContext* getOperationContext() { return _txn; }
 
         // TODO(spencer): SERVER-10228 SERVER-14779 Remove this/move it fully into OperationContext.
         bool isInDirectClient() const { return _inDirectClient; }