Require what to be notified for with block and Subprocess.execute

There was an issue before where the stdin buffer would always have space
so it would always yield that block and Ruby would spin at 100%. Now we
require all callers to say what they want to listen for. This drops
CPU down to almost nothing.

See GH-832

lib/vagrant/driver/virtualbox_base.rb

@@ -314,6 +314,9 @@ module Vagrant
           @logger.info("Interrupted.")
         end
 
+        # Append in the options for subprocess
+        command << { :notify => [:stdout, :stderr] }
+
         Util::Busy.busy(int_callback) do
           Subprocess.execute(@vboxmanage_path, *command, &block)
         end

lib/vagrant/easy/operations.rb

@@ -63,7 +63,7 @@ module Vagrant
           end
         end
 
-        Vagrant::Util::Subprocess.execute(command, &block)
+        Vagrant::Util::Subprocess.execute(command, :notify => [:stdout, :stderr], &block)
       end
 
       # Run a shell command within the VM. The command will run within a

lib/vagrant/util/subprocess.rb

@@ -29,8 +29,27 @@ module Vagrant
       def execute
         # Get the timeout, if we have one
         timeout = @options[:timeout]
+
+        # Get the working directory
         workdir = @options[:workdir] || Dir.pwd
 
+        # Get what we're interested in being notified about
+        notify  = @options[:notify] || []
+        notify  = [notify] if !notify.is_a?(Array)
+        if notify.empty? && block_given?
+          # If a block is given, subscribers must be given, otherwise the
+          # block is never called. This is usually NOT what you want, so this
+          # is an error.
+          message = "A list of notify subscriptions must be given if a block is given"
+          raise ArgumentError, message
+        end
+
+        # Let's get some more useful booleans that we access a lot so
+        # we're not constantly calling an `include` check
+        notify_stderr = notify.include?(:stderr)
+        notify_stdin  = notify.include?(:stdin)
+        notify_stdout = notify.include?(:stdout)
+
         # Build the ChildProcess
         @logger.info("Starting process: #{@command.inspect}")
         process = ChildProcess.build(*@command)
@@ -80,7 +99,8 @@ module Vagrant
 
         @logger.debug("Selecting on IO")
         while true
-          results = IO.select([stdout, stderr], [process.io.stdin], nil, timeout || 5)
+          writers = notify_stdin ? [process.io.stdin] : []
+          results = IO.select([stdout, stderr], writers, nil, timeout || 5)
           readers, writers = results
 
           # Check if we have exceeded our timeout

test/acceptance/support/isolated_environment.rb

@@ -51,7 +51,8 @@ module Acceptance
       options = argN.last.is_a?(Hash) ? argN.pop : {}
       options = {
         :workdir => @workdir,
-        :env     => @env
+        :env     => @env,
+        :notify  => [:stdin, :stderr, :stdout]
       }.merge(options)
 
       # Add the options to be passed on
@@ -59,7 +60,7 @@ module Acceptance
 
       # Execute, logging out the stdout/stderr as we get it
       @logger.info("Executing: #{[command].concat(argN).inspect}")
-      Vagrant::Util::Subprocess.execute(command, *argN) do |type, data|
+      Vagrant::Util::Subprocess.execute(command *argN) do |type, data|
         @logger.debug("#{type}: #{data}") if type == :stdout || type == :stderr
         yield type, data if block_given?
       end