Synonyms Support

The synonym data structure is a set of groups, each group contains synonym terms. For example, the following synonym data structure contains three groups, each group contains three synonym terms:

We use a simple HashMap to map between the terms and the group ids. During building the index, we check if the current term appears in the synonym map, and if it does we take all the group ids that the term belongs to.

Since the indexing is performed in a separate thread, the synonyms map may change during the indexing, which in turn may cause data corruption or crashes during indexing/searches. To solve this issue, we create a read-only copy for indexing purposes. The read-only copy is maintained using ref count.