Add a option to disable idle gc.

If a Bazel server is idle for 10 seconds, it unconditionally triggers a full-scale Java GC via System.gc(). This behavior doesn't have clear benefits and causes Bazel to steal resources from whatever the user does after invoking Bazel. This CL adds a startup option, --idle_server_tasks, to toggle the idle GC behavior.

Also, add some logging for when idle GC is enabled, so it's easier to evaluate its effects. Example of logging:
```
180718 17:43:04.609:I 247 [com.google.devtools.build.lib.server.IdleServerTasks.lambda$idle$0] [Idle GC] used: 157MB -> 15MB, committed: 421MB -> 422MB
```

Fixes https://github.com/bazelbuild/bazel/issues/5589.

Closes #5628.

PiperOrigin-RevId: 207869996

3 files changed, 15 insertions, 0 deletions

diff --git a/src/main/cpp/blaze.cc b/src/main/cpp/blaze.cc
index 9e7d979855..801a9314c0 100644
--- a/src/main/cpp/blaze.cc
+++ b/src/main/cpp/blaze.cc
@@ -541,6 +541,11 @@ static vector<string> GetArgumentArray(
     // being "null" to set the programmatic default in the server.
     result.push_back("--digest_function=" + globals->options->digest_function);
   }
+  if (globals->options->idle_server_tasks) {
+    result.push_back("--idle_server_tasks");
+  } else {
+    result.push_back("--noidle_server_tasks");
+  }
   if (globals->options->oom_more_eagerly) {
     result.push_back("--experimental_oom_more_eagerly");
   } else {
diff --git a/src/main/cpp/startup_options.cc b/src/main/cpp/startup_options.cc
index a2d26b74d3..c54728f92e 100644
--- a/src/main/cpp/startup_options.cc
+++ b/src/main/cpp/startup_options.cc
@@ -93,6 +93,7 @@ StartupOptions::StartupOptions(const string &product_name,
           "com.google.devtools.build.lib.util.SingleLineFormatter"),
       expand_configs_in_place(true),
       digest_function(),
+      idle_server_tasks(true),
       original_startup_options_(std::vector<RcStartupFlag>()) {
   bool testing = !blaze::GetEnv("TEST_TMPDIR").empty();
   if (testing) {
@@ -133,6 +134,7 @@ StartupOptions::StartupOptions(const string &product_name,
   RegisterNullaryStartupFlag("experimental_oom_more_eagerly");
   RegisterNullaryStartupFlag("fatal_event_bus_exceptions");
   RegisterNullaryStartupFlag("host_jvm_debug");
+  RegisterNullaryStartupFlag("idle_server_tasks");
   RegisterNullaryStartupFlag("ignore_all_rc_files");
   RegisterNullaryStartupFlag("watchfs");
   RegisterNullaryStartupFlag("write_command_log");
@@ -334,6 +336,12 @@ blaze_exit_code::ExitCode StartupOptions::ProcessArg(
   } else if (GetNullaryOption(arg, "--noexpand_configs_in_place")) {
     expand_configs_in_place = false;
     option_sources["expand_configs_in_place"] = rcfile;
+  } else if (GetNullaryOption(arg, "--idle_server_tasks")) {
+    idle_server_tasks = true;
+    option_sources["idle_server_tasks"] = rcfile;
+  } else if (GetNullaryOption(arg, "--noidle_server_tasks")) {
+    idle_server_tasks = false;
+    option_sources["idle_server_tasks"] = rcfile;
   } else if ((value = GetUnaryOption(arg, next_arg,
                                      "--connect_timeout_secs")) != NULL) {
     if (!blaze_util::safe_strto32(value, &connect_timeout_secs) ||
diff --git a/src/main/cpp/startup_options.h b/src/main/cpp/startup_options.h
index cca38369c3..9f4cd0c622 100644
--- a/src/main/cpp/startup_options.h
+++ b/src/main/cpp/startup_options.h
@@ -301,6 +301,8 @@ class StartupOptions {
   // The hash function to use when computing file digests.
   std::string digest_function;
 
+  bool idle_server_tasks;
+
   // The startup options as received from the user and rc files, tagged with
   // their origin. This is populated by ProcessArgs.
   std::vector<RcStartupFlag> original_startup_options_;