params: safe and efficient async writing parameters (#25912)

* Safe and efficient asynchronous writing parameters

* call putNonBlocking in locationd

* remove space

* ->AsyncWriter

* remove semicolon

* use member function

* asyc write multiple times

* add test case for AsyncWriter

* merge master

* add missing include

* public

* cleanup

* create once

* cleanup

* update that

* explicit waiting

* improve test case

---------

Co-authored-by: Adeeb Shihadeh <adeebshihadeh@gmail.com>
old-commit-hash: 0d797f4e8b2552192669d0329c14849f0a970066

common/params.cc

@@ -7,6 +7,7 @@
 #include <csignal>
 #include <unordered_map>
 
+#include "common/queue.h"
 #include "common/swaglog.h"
 #include "common/util.h"
 #include "system/hardware/hw.h"
@@ -327,3 +328,33 @@ void Params::clearAll(ParamKeyType key_type) {
 
   fsync_dir(getParamPath());
 }
+
+void Params::putNonBlocking(const std::string &key, const std::string &val) {
+  static AsyncWriter async_writer;
+  async_writer.queue({params_path, key, val});
+}
+
+
+// AsyncWriter
+
+AsyncWriter::~AsyncWriter() {
+  if (future.valid()) {
+    future.wait();
+  }
+}
+
+void AsyncWriter::queue(const std::tuple<std::string, std::string, std::string> &dat) {
+  q.push(dat);
+  // start thread on demand
+  if (!future.valid() || future.wait_for(std::chrono::milliseconds(0)) == std::future_status::ready) {
+    future = std::async(std::launch::async, &AsyncWriter::write, this);
+  }
+}
+
+void AsyncWriter::write() {
+  std::tuple<std::string, std::string, std::string> dat;
+  while (q.try_pop(dat, 0)) {
+    auto &[path, key, value] = dat;
+    Params(path).put(key, value);
+  }
+}