[remoting host][linux] Add a watchdog for the IgnoreXServerGrabs

Per crbug.com/1130090, it appears that it's the call to
IgnoreXServerGrabs() that has been blocking the network thread on the
prober VMs.

This CL adds a watchdog that monitors the time it takes to call
IgnoreXServerGrabs() and crashes the host if it takes too long. This
doesn't fix the underlying problem of IgnoreXServerGrabs() being
blocky, but should be sufficient to calm down the probers, and
prove/disprove the hypothesis.

Bug: 1130090
Change-Id: I63954b4cdf72a2015344a4900d3e1ce6f9e5ae81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2725026
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#858376}

remoting/host/basic_desktop_environment.cc

@@ -29,12 +29,46 @@
 #endif
 
 #if defined(USE_X11)
+#include "base/threading/watchdog.h"
 #include "remoting/host/linux/x11_util.h"
 #include "ui/base/ui_base_features.h"
 #endif
 
 namespace remoting {
 
+#if defined(USE_X11)
+
+namespace {
+
+// The maximum amount of time we will wait for the IgnoreXServerGrabs() to
+// return before we crash the host.
+constexpr base::TimeDelta kWaitForIgnoreXServerGrabsTimeout =
+    base::TimeDelta::FromSeconds(30);
+
+// Helper class to monitor the call to
+// webrtc::SharedXDisplay::IgnoreXServerGrabs() (on a temporary thread), which
+// has been observed to occasionally hang forever and zombify the host.
+// This class crashes the host if the IgnoreXServerGrabs() call takes too long,
+// so that the ME2ME daemon process can respawn the host.
+// See: crbug.com/1130090
+class IgnoreXServerGrabsWatchdog : public base::Watchdog {
+ public:
+  IgnoreXServerGrabsWatchdog()
+      : base::Watchdog(kWaitForIgnoreXServerGrabsTimeout,
+                       "IgnoreXServerGrabs Watchdog",
+                       /* enabled= */ true) {}
+  ~IgnoreXServerGrabsWatchdog() override = default;
+
+  void Alarm() override {
+    // Crash the host if IgnoreXServerGrabs() takes too long.
+    CHECK(false) << "IgnoreXServerGrabs() timed out.";
+  }
+};
+
+}  // namespace
+
+#endif  // defined(USE_X11)
+
 BasicDesktopEnvironment::~BasicDesktopEnvironment() {
   DCHECK(caller_task_runner_->BelongsToCurrentThread());
 }
@@ -131,8 +165,15 @@ BasicDesktopEnvironment::BasicDesktopEnvironment(
       options_(options) {
   DCHECK(caller_task_runner_->BelongsToCurrentThread());
 #if defined(USE_X11)
-  if (!features::IsUsingOzonePlatform())
+  if (!features::IsUsingOzonePlatform()) {
+    // TODO(yuweih): The watchdog is just to test the hypothesis.
+    // The IgnoreXServerGrabs() call should probably be moved to whichever
+    // thread that created desktop_capture_options().x_display().
+    IgnoreXServerGrabsWatchdog watchdog;
+    watchdog.Arm();
     desktop_capture_options().x_display()->IgnoreXServerGrabs();
+    watchdog.Disarm();
+  }
 #elif defined(OS_WIN)
   // The options passed to this instance are determined by a process running in
   // Session 0.  Access to DirectX functions in Session 0 is limited so the