query x server to wait for launch

Author: ianfixes

lib/arduino_ci/display_manager.rb

@@ -2,6 +2,8 @@
 require 'singleton'
 require 'timeout'
 
+DESIRED_DISPLAY = ":1.0".freeze
+
 module ArduinoCI
 
   # When arduino commands run, they need a graphical display.
@@ -24,6 +26,42 @@ def existing_display?
       false
     end
 
+    # check whether a process is alive
+    # https://stackoverflow.com/a/32513298/2063546
+    def alive?(pid)
+      Process.kill(0, pid)
+      true
+    rescue
+      false
+    end
+
+    # check whether an X server is taking connections
+    def xserver_exist?(display)
+      system({ "DISPLAY" => display }, "xdpyinfo", out: File::NULL, err: File::NULL)
+    end
+
+    # wait for the xvfb command to launch
+    # @param display [String] the value of the DISPLAY env var
+    # @param pid [Int] the process of Xvfb
+    # @param timeout [Int] the timeout in seconds
+    # @return [Bool] whether we detected a launch
+    def xvfb_launched?(display, pid, timeout)
+      Timeout.timeout(timeout) do
+        loop do
+          unless alive? pid
+            puts "Xvfb process has died"
+            return false
+          end
+          x = xserver_exist? display
+          puts "xdpyinfo reports X server status as #{x}"
+          return true if x
+          sleep(0.1)
+        end
+      end
+    rescue Timeout::Error
+      false
+    end
+
     # enable a virtual display
     def enable
       if @existing
@@ -35,14 +73,18 @@ def enable
       return unless @pid.nil?  # TODO: disable first?
 
       # open Xvfb
-      xvfb_cmd = ["Xvfb", ":1", "-ac", "-screen", "0", "1280x1024x16"]
+      xvfb_cmd = [
+        "Xvfb",
+        "+extension", "RANDR",
+        ":1",
+        "-ac",
+        "-screen", "0",
+        "1280x1024x16",
+      ]
       puts "pipeline_start for Xvfb"
       pipe = IO.popen(xvfb_cmd)
       @pid = pipe.pid
-      sleep(3)  # TODO: test a connection to the X server?
-      @enabled = true
-      puts "\n\nxdpyinfo:\n\n"
-      system(environment, "xdpyinfo")
+      @enabled = xvfb_launched?(DESIRED_DISPLAY, @pid, 30)
     end
 
     # disable the virtual display
@@ -106,7 +148,7 @@ def run_silent(*args)
     def environment
       return nil unless @existing || @enabled
       return {} if @existing
-      { "DISPLAY" => ":1.0" }
+      { "DISPLAY" => DESIRED_DISPLAY }
     end
 
     # On finalize, ensure child process is ended