Avoid gpu watchdog crash on timeout if X is un-responsive.

content/gpu/gpu_watchdog_thread.cc

Index: content/gpu/gpu_watchdog_thread.cc
diff --git a/content/gpu/gpu_watchdog_thread.cc b/content/gpu/gpu_watchdog_thread.cc
index 02b6bff8040e8f6c7c464f309c31761da0f508f9..5c022a7ca6305aa76170d6308825081056a9f683 100644
--- a/content/gpu/gpu_watchdog_thread.cc
+++ b/content/gpu/gpu_watchdog_thread.cc
@@ -19,6 +19,13 @@
 #include "content/public/common/content_switches.h"
 #include "content/public/common/result_codes.h"
 
+#if defined(USE_X11)
+extern "C" {
+#include <X11/Xlib.h>
+}
+#include "ui/gfx/x/x11_types.h"
+#endif
+
 namespace content {
 namespace {
 const int64 kCheckPeriodMs = 2000;
@@ -39,6 +46,9 @@ GpuWatchdogThread::GpuWatchdogThread(int timeout)
 #endif
       task_observer_(this),
       suspended_(false),
+#if defined(USE_X11)
+      x_server_active(true),
+#endif
       weak_factory_(this) {
   DCHECK(timeout >= 0);
 
@@ -184,14 +194,25 @@ void GpuWatchdogThread::OnCheck(bool after_suspend) {
       FROM_HERE,
       base::Bind(&base::DoNothing));
 
-  // Post a task to the watchdog thread to exit if the monitored thread does
-  // not respond in time.
-  message_loop()->PostDelayedTask(
-      FROM_HERE,
-      base::Bind(
-          &GpuWatchdogThread::DeliberatelyTerminateToRecoverFromHang,
-          weak_factory_.GetWeakPtr()),
-      timeout);
+#if defined(USE_X11)
+  // Post a task to the watchdog thread to check XServer is active
+  // if the monitored thread does not respond in time.
+  if (x_server_active) {
+    message_loop()->PostDelayedTask(
+        FROM_HERE, base::Bind(&GpuWatchdogThread::CheckXServerActive,
+                              weak_factory_.GetWeakPtr()),
+        timeout);
+  } else
+#endif
+  {
+    // Post a task to the watchdog thread to exit if the monitored thread does
+    // not respond in time.
+    message_loop()->PostDelayedTask(
+        FROM_HERE,
+        base::Bind(&GpuWatchdogThread::DeliberatelyTerminateToRecoverFromHang,
+                   weak_factory_.GetWeakPtr()),
+        timeout);
+  }
 }
 
 // Use the --disable-gpu-watchdog command line switch to disable this.
@@ -259,6 +280,16 @@ void GpuWatchdogThread::DeliberatelyTerminateToRecoverFromHang() {
   terminated = true;
 }
 
+#if defined(USE_X11)
+void GpuWatchdogThread::CheckXServerActive() {
+  if (!XDisplayString(gfx::GetXDisplay())) {

[danakj, 2015/01/06 00:29:19]

What does this do if the X server is not the active VT?

[sohanjg, 2015/01/06 12:21:45]

Hmm..i was assuming this would return NULL in that case, but there is no
documentation for it.
But it seems, in OpenNewXDisplay, we send display string as NULL, so this query
wouldnt be of much help i guess.

My idea was to use a less complex X-api do that we do not need to plumb all the
params that XChangeProperty would have required in gpu wtachdog thread.

We may also use, XDefaultScreen, and XDisplayHeight to get display height. And i
assume (not documented though) we will get it as 0, if X is not active VT.
Please suggest what should be best here.

I checked fgconsole man page,
http://man7.org/linux/man-pages/man1/fgconsole.1.html 
It seems if we check --next-available param here, we may understand whether X is
the active VT.
But would that help?

+    x_server_active = false;
+    timeout_ /= 2;
+  } else {
+    x_server_active = true;
+  }
+}
+#endif
 void GpuWatchdogThread::AddPowerObserver() {
   message_loop()->PostTask(
       FROM_HERE,