This page documents the order of creation and destruction for libmongoc’s main struct types.
Clients and pools#
A program that uses libmongoc from multiple threads should create a mongoc_client_pool_t with mongoc_client_pool_new(). Each thread acquires a mongoc_client_t from the pool with mongoc_client_pool_pop() and returns it with mongoc_client_pool_push() when the thread is finished using it. To destroy the pool, first return all clients, then call mongoc_client_pool_destroy().
You can create a mongoc_gridfs_t from a mongoc_client_t, create a mongoc_gridfs_file_t or mongoc_gridfs_file_list_t from a mongoc_gridfs_t, create a mongoc_gridfs_file_t from a mongoc_gridfs_file_list_t, and create a mongoc_stream_t from a mongoc_gridfs_file_t.
Each of these objects depends on the object it was created from. Always destroy GridFS objects in the reverse of the order they were created. The sole exception is that a mongoc_gridfs_file_t need not be destroyed before the mongoc_gridfs_file_list_t it was created from.
GridFS bucket objects#
Create mongoc_gridfs_bucket_t with a mongoc_database_t derived from a mongoc_client_t. The mongoc_database_t is independent from the mongoc_gridfs_bucket_t. But the mongoc_client_t must outlive the mongoc_gridfs_bucket_t.
Start a session with mongoc_client_start_session(), use the session for a sequence of operations and multi-document transactions, then free it with mongoc_client_session_destroy(). Any mongoc_cursor_t or mongoc_change_stream_t using a session must be destroyed before the session, and a session must be destroyed before the mongoc_client_t it came from.
By default, sessions are causally consistent. To disable causal consistency, before starting a session create a mongoc_session_opt_t with mongoc_session_opts_new() and call mongoc_session_opts_set_causal_consistency(), then free the struct with mongoc_session_opts_destroy().
Unacknowledged writes are prohibited with sessions.
A mongoc_client_session_t must be used by only one thread at a time. Due to session pooling, mongoc_client_start_session() may return a session that has been idle for some time and is about to be closed after its idle timeout. Use the session within one minute of acquiring it to refresh the session and avoid a timeout.
Client Side Encryption#
When configuring a mongoc_client_t for automatic encryption via mongoc_client_enable_auto_encryption(), if a separate key vault client is set in the options (via mongoc_auto_encryption_opts_set_keyvault_client()) the key vault client must outlive the encrypted client.
When configuring a mongoc_client_pool_t for automatic encryption via mongoc_client_pool_enable_auto_encryption(), if a separate key vault client pool is set in the options (via mongoc_auto_encryption_opts_set_keyvault_client_pool()) the key vault client pool must outlive the encrypted client pool.
When creating a mongoc_client_encryption_t, the configured key vault client (set via mongoc_client_encryption_opts_set_keyvault_client()) must outlive the mongoc_client_encryption_t.