OUT: Threshold above which storage of a shared object header message index shifts from list to B-tree
OUT: Threshold below which storage of a shared object header message index reverts to list format
H5Pget_shared_mesg_phase_change retrieves the threshold values for storage of shared object header message indexes in a file. These phase change thresholds determine the point at which the index storage mechanism changes from a more compact list format to a more performance-oriented B-tree format, and vice-versa.
By default, a shared object header message index is initially stored as a compact list. When the number of messages in an index exceeds the specified max_list threshold, storage switches to a B-tree format for improved performance. If the number of messages subsequently falls below the min_btree threshold, the index will revert to the list format.
If max_list is set to 0 (zero), shared object header message indexes in the file will always be stored as B-trees.
fcpl_id specifies the file creation property list.
Returns a non-negative value if successful; otherwise returns a negative value.