From e309712bd1c7b210187018003e8f3141c56bd8ce Mon Sep 17 00:00:00 2001
From: Evan Klitzke <evan@eklitzke.org>
Date: Mon, 2 Dec 2019 11:10:24 -0800
Subject: [PATCH] Default to using 80% of cores available (instead of 100%) for
 indexing

---
 src/config.cc              | 9 +++++++++
 src/config.hh              | 6 +++++-
 src/messages/initialize.cc | 4 ++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/config.cc b/src/config.cc
index 659956b0..97cb80cf 100644
--- a/src/config.cc
+++ b/src/config.cc
@@ -3,6 +3,9 @@
 
 #include "config.hh"
 
+#include <algorithm>
+#include <thread>
+
 namespace ccls {
 Config *g_config;
 
@@ -16,4 +19,10 @@ void doPathMapping(std::string &arg) {
     }
   }
 }
+
+int defaultIndexThreadCount() {
+  constexpr float kIndexThreadUtilization = 0.8;
+  return std::max(1, static_cast<int>(std::thread::hardware_concurrency() *
+                                      kIndexThreadUtilization));
+}
 } // namespace ccls
diff --git a/src/config.hh b/src/config.hh
index 751a712c..6ab1ba9f 100644
--- a/src/config.hh
+++ b/src/config.hh
@@ -8,6 +8,10 @@
 #include <string>
 
 namespace ccls {
+
+// Select a reasonable default number of threads to use for indexing.
+int defaultIndexThreadCount();
+
 /*
 The language client plugin needs to send initialization options in the
 `initialize` request to the ccls language server.
@@ -286,7 +290,7 @@ struct Config {
     bool parametersInDeclarations = true;
 
     // Number of indexer threads. If 0, 80% of cores are used.
-    int threads = 0;
+    int threads = defaultIndexThreadCount();
 
     // Whether to reparse a file if write times of its dependencies have
     // changed. The file will always be reparsed if its own write time changes.
diff --git a/src/messages/initialize.cc b/src/messages/initialize.cc
index b015d98d..691b56a0 100644
--- a/src/messages/initialize.cc
+++ b/src/messages/initialize.cc
@@ -374,6 +374,10 @@ void do_initialize(MessageHandler *m, InitializeParam &param,
   // Start indexer threads. Start this after loading the project, as that
   // may take a long time. Indexer threads will emit status/progress
   // reports.
+  //
+  // By default config.hh will select 80% of the available cores to use as
+  // index threads, but explicitly specifying threads=0 will instead use all
+  // available cores.
   if (g_config->index.threads == 0)
     g_config->index.threads = (int)std::thread::hardware_concurrency();