use SCHED_BATCH scheduling priority for indexing threads

src/messages/initialize.cc

@@ -255,6 +255,7 @@ void *indexer(void *arg_) {
   delete arg;
   std::string name = "indexer" + std::to_string(idx);
   set_thread_name(name.c_str());
+  setBatchPriority();
   pipeline::indexer_Main(h->manager, h->vfs, h->project, h->wfiles);
   pipeline::threadLeave();
   return nullptr;

src/platform.hh

@@ -17,4 +17,6 @@ void freeUnusedMemory();
 void traceMe();
 
 void spawnThread(void *(*fn)(void *), void *arg);
+
+void setBatchPriority();
 } // namespace ccls

src/platform_posix.cc

@@ -4,6 +4,7 @@
 #if defined(__unix__) || defined(__APPLE__)
 #include "platform.hh"
 
+#include "log.hh"
 #include "utils.hh"
 
 #include <assert.h>
@@ -17,6 +18,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
+#include <sched.h>
 #include <signal.h>
 #include <sys/resource.h>
 #include <sys/stat.h>
@@ -75,6 +77,26 @@ void spawnThread(void *(*fn)(void *), void *arg) {
   pthread_create(&thd, &attr, fn, arg);
   pthread_attr_destroy(&attr);
 }
+
+void setBatchPriority() {
+#ifdef SCHED_BATCH
+  pid_t this_thread_id = gettid();
+
+  // get a sched_param with the existing thread sched_priority
+  errno = 0;
+  struct sched_param p;
+  p.sched_priority = getpriority(PRIO_PROCESS, this_thread_id);
+  if (p.sched_priority == -1 && errno != 0) {
+    LOG_S(ERROR) << "failed to getpriority(): " << strerror(errno);
+    return;
+  }
+
+  // retain the existing sched_priority, but use SCHED_BATCH policy
+  if (sched_setscheduler(this_thread_id, SCHED_BATCH, &p) == -1) {
+    LOG_S(ERROR) << "failed to sched_setscheduler(): " << strerror(errno);
+  }
+}
+#endif
 } // namespace ccls
 
 #endif

src/platform_win.cc

@@ -48,6 +48,8 @@ void traceMe() {}
 void spawnThread(void *(*fn)(void *), void *arg) {
   std::thread(fn, arg).detach();
 }
+
+void setBatchPriority() {}
 } // namespace ccls
 
 #endif