// this is the slowest, but tests the writer concurrency when no caching is done.
// only pick it during NIGHTLY tests, and even then, with very low chances.
cache = NO_OP_CACHE;
} else {
// this is slower than CL2O, but less memory consuming, and exercises finding categories on disk too.
cache = new LruTaxonomyWriterCache(ncats / 10);
}
final DirectoryTaxonomyWriter tw = new DirectoryTaxonomyWriter(dir, OpenMode.CREATE, cache);
Thread[] addThreads = new Thread[atLeast(4)];
for (int z = 0; z < addThreads.length; z++) {
addThreads[z] = new Thread() {