Make session monitor communication async

NEWS.md

@@ -45,3 +45,4 @@
 * Fixed failure to open files after an attempt to open a very large file (#6637)
 * Fixed Data Viewer getting out of sync with the underlying data when changing live viewer object (#1819)
 * Fixed issue where attempts to plot could fail if R tempdir was deleted (#2214)
+* Fixed issue that caused sessions to freeze due to slow I/O for monitor logs (Pro #1259)

src/cpp/session/SessionMain.cpp

@@ -1662,17 +1662,33 @@ bool ensureUtf8Charset()
 #endif
 }
 
+// io_service for performing monitor work on the thread
+boost::asio::io_service s_ioService;
+
+void monitorWorkerThreadFunc()
+{
+ boost::asio::io_service::work work(s_ioService);
+ s_ioService.run();
+}
+
 void initMonitorClient()
 {
  if (!options().getBoolOverlayOption(kLauncherSessionOption))
  {
  monitor::initializeMonitorClient(core::system::getenv(kMonitorSocketPathEnvVar),
- options().monitorSharedSecret());
+ options().monitorSharedSecret(),
+ s_ioService);
  }
  else
  {
- modules::overlay::initMonitorClient();
+ modules::overlay::initMonitorClient(s_ioService);
  }
+
+ // start the monitor work thread
+ // we handle monitor calls in a separate thread to ensure that calls
+ // to the monitor (which are likely across machines and thus very expensive)
+ // do not hamper the liveliness of the session as a whole
+ core::thread::safeLaunchThread(monitorWorkerThreadFunc);
 }
 
 } // anonymous namespace

src/cpp/session/modules/overlay/SessionOverlay.cpp

@@ -49,7 +49,7 @@ int verifyInstallation()
  return EXIT_SUCCESS;
 }
 
-void initMonitorClient()
+void initMonitorClient(boost::asio::io_service& ioService)
 {
 }
 

src/cpp/session/modules/overlay/SessionOverlay.hpp

@@ -17,6 +17,7 @@
 #define SESSION_OVERLAY_HPP
 
 #include <string>
+#include <boost/asio/io_service.hpp>
 
 namespace rstudio {
 namespace core {
@@ -38,7 +39,7 @@ void streamLauncherOutput(const std::string& jobId,
 
 int verifyInstallation();
 
-void initMonitorClient();
+void initMonitorClient(boost::asio::io_service& ioService);
 
 core::Error initialize();