Automatically compute a good value for number of indexer threads to start.

src/command_line.cc

@@ -1673,8 +1673,11 @@ void QueryDbMain(IndexerConfig* config) {
   FileConsumer::SharedState file_consumer_shared;
 
   // Start indexer threads.
-  std::cerr << "[querydb] Starting " << config->indexerCount << " indexers" << std::endl;
-  for (int i = 0; i < config->indexerCount; ++i) {
+  int indexerCount = std::min<int>(std::thread::hardware_concurrency(), 2) - 1;
+  if (config->indexerCount > 0)
+    indexerCount = config->indexerCount;
+  std::cerr << "[querydb] Starting " << indexerCount << " indexers" << std::endl;
+  for (int i = 0; i < indexerCount; ++i) {
     new std::thread([&]() {
       IndexMain(config, &file_consumer_shared, &project, &queue_do_index, &queue_do_id_map, &queue_on_id_mapped, &queue_on_indexed);
     });

src/language_server_api.h

@@ -59,9 +59,14 @@ struct IndexerConfig {
   std::string cacheDirectory;
   NonElidedVector<std::string> whitelist;
   NonElidedVector<std::string> blacklist;
-  int indexerCount = 1;
-  int maxWorkspaceSearchResults = 1000;
   std::vector<std::string> extraClangArguments;
+
+  // Maximum workspace search results.
+  int maxWorkspaceSearchResults = 1000;
+
+  // Force a certain number of indexer threads. If less than 1 a default value
+  // should be used.
+  int indexerCount = 0;
   // If false, the indexer will be disabled.
   bool enableIndexing = true;
   // If false, indexed files will not be written to disk.
@@ -72,9 +77,10 @@ struct IndexerConfig {
 MAKE_REFLECT_STRUCT(IndexerConfig,
   cacheDirectory,
   whitelist, blacklist,
-  indexerCount,
-  maxWorkspaceSearchResults,
   extraClangArguments,
+
+  maxWorkspaceSearchResults,
+  indexerCount,
   enableIndexing, enableCacheWrite, enableCacheRead);