From d363d0322ddb3ea71c857de9fbeef9e857693d19 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Florian=20N=C3=BCcke?= <florian@nuecke.de>
Date: Sun, 6 Oct 2013 18:16:03 +0200
Subject: [PATCH] changed os.clock to be the actual cpu time of the computer
 and introduced os.uptime as the replacement of the old functionality; dofile
 now properly throws when loading fails; graphicscard now stores the screen
 its bound to in the component, which allows for the computer to display
 messages after it crashed (by sending a display request to neighbors ->
 graphicscards installed in it); fixed potential timeout in os.signal;
 wrappers for pcall and xpcall to enforce timeout when they return, too

---
 .../opencomputers/lua/drivers/filesystem.lua  |  2 +-
 assets/opencomputers/lua/drivers/gpu.lua      | 94 +++++++++---------
 assets/opencomputers/lua/kernel.lua           | 23 ++++-
 assets/opencomputers/lua/rom/api/event.lua    | 10 +-
 assets/opencomputers/lua/rom/api/term.lua     | 98 ++++++++++---------
 assets/opencomputers/lua/rom/bin/sh.lua       |  8 +-
 li/cil/oc/server/component/Computer.scala     | 75 +++++++++-----
 li/cil/oc/server/component/GraphicsCard.scala | 74 ++++++++++----
 li/cil/oc/server/network/Network.scala        | 32 ++++--
 9 files changed, 262 insertions(+), 154 deletions(-)

diff --git a/assets/opencomputers/lua/drivers/filesystem.lua b/assets/opencomputers/lua/drivers/filesystem.lua
index 7bdf7f708..b7e87abd6 100644
--- a/assets/opencomputers/lua/drivers/filesystem.lua
+++ b/assets/opencomputers/lua/drivers/filesystem.lua
@@ -590,7 +590,7 @@ end
 function dofile(filename)
   local program, reason = loadfile(filename)
   if not program then
-    return nil, reason
+    return error(reason)
   end
   return program()
 end
diff --git a/assets/opencomputers/lua/drivers/gpu.lua b/assets/opencomputers/lua/drivers/gpu.lua
index c3c17a3b0..5bfcfd7fe 100644
--- a/assets/opencomputers/lua/drivers/gpu.lua
+++ b/assets/opencomputers/lua/drivers/gpu.lua
@@ -1,48 +1,52 @@
 driver.gpu = {}
 
-function driver.gpu.setResolution(gpu, screen, w, h)
-  send(gpu, "gpu.resolution=", screen, w, h)
-end
-
-function driver.gpu.getResolution(gpu, screen)
-  return send(gpu, "gpu.resolution", screen)
-end
-
-function driver.gpu.getResolutions(gpu, screen)
-  return send(gpu, "gpu.resolutions", screen)
-end
-
-function driver.gpu.set(gpu, screen, col, row, value)
-  send(gpu, "gpu.set", screen, col, row, value)
-end
-
-function driver.gpu.fill(gpu, screen, col, row, w, h, value)
-  send(gpu, "gpu.fill", screen, col, row, w, h, value:sub(1, 1))
-end
-
-function driver.gpu.copy(gpu, screen, col, row, w, h, tx, ty)
-  send(gpu, "gpu.copy", screen, col, row, w, h, tx, ty)
-end
-
 function driver.gpu.bind(gpu, screen)
-  return {
-    setResolution = function(w, h)
-     driver.gpu.setResolution(gpu, screen, w, h)
-    end,
-    getResolution = function()
-     return driver.gpu.getResolution(gpu, screen)
-    end,
-    getResolutions = function()
-     return driver.gpu.getResolutions(gpu, screen)
-    end,
-    set = function(col, row, value)
-      driver.gpu.set(gpu, screen, col, row, value)
-    end,
-    fill = function(col, ro, w, h, value)
-      driver.gpu.fill(gpu, screen, col, ro, w, h, value)
-    end,
-    copy = function(col, row, w, h, tx, ty)
-      driver.gpu.copy(gpu, screen, col, row, w, h, tx, ty)
-    end
-  }
-end
\ No newline at end of file
+  checkArg(1, gpu, "string")
+  checkArg(2, screen, "string")
+  return send(gpu, "gpu.bind", screen)
+end
+
+function driver.gpu.resolution(gpu, w, h)
+  checkArg(1, gpu, "string")
+  if w and h then
+    checkArg(2, w, "number")
+    checkArg(3, h, "number")
+    return send(gpu, "gpu.resolution=", w, h)
+  else
+    return send(gpu, "gpu.resolution")
+  end
+end
+
+function driver.gpu.resolutions(gpu)
+  checkArg(1, gpu, "string")
+  return send(gpu, "gpu.resolutions")
+end
+
+function driver.gpu.set(gpu, col, row, value)
+  checkArg(1, gpu, "string")
+  checkArg(2, col, "number")
+  checkArg(3, row, "number")
+  checkArg(4, value, "string")
+  return send(gpu, "gpu.set", col, row, value)
+end
+
+function driver.gpu.fill(gpu, col, row, w, h, value)
+  checkArg(1, gpu, "string")
+  checkArg(2, col, "number")
+  checkArg(3, row, "number")
+  checkArg(4, w, "number")
+  checkArg(5, h, "number")
+  checkArg(6, value, "string")
+  return send(gpu, "gpu.fill", col, row, w, h, value:sub(1, 1))
+end
+
+function driver.gpu.copy(gpu, col, row, w, h, tx, ty)
+  checkArg(1, gpu, "string")
+  checkArg(2, col, "number")
+  checkArg(3, row, "number")
+  checkArg(4, w, "number")
+  checkArg(5, h, "number")
+  checkArg(6, tx, "number")
+  checkArg(7, ty, "number")
+  return send(gpu, "gpu.copy", col, row, w, h, tx, ty)
+end
diff --git a/assets/opencomputers/lua/kernel.lua b/assets/opencomputers/lua/kernel.lua
index f959db31c..81efdceaf 100644
--- a/assets/opencomputers/lua/kernel.lua
+++ b/assets/opencomputers/lua/kernel.lua
@@ -91,6 +91,7 @@ local sandbox = {
     date = os.date,
     difftime = os.difftime,
     time = os.time,
+    uptime = os.uptime,
     freeMemory = os.freeMemory,
     totalMemory = os.totalMemory,
     address = os.address,
@@ -138,7 +139,7 @@ function sandbox.checkArg(n, have, ...)
     end
   end
   local msg = "bad argument #" .. n .. " (" .. table.concat({...}, " or ") .. " expected, got " .. have .. ")"
-  error(debug.traceback(msg, 3), 2)
+  error(debug.traceback(msg, 2), 2)
 end
 
 -------------------------------------------------------------------------------
@@ -204,6 +205,18 @@ function sandbox.coroutine.yield(...)
   return coroutine.yield(nil, ...)
 end
 
+function sandbox.pcall(...)
+  local result = table.pack(pcall(...))
+  checkDeadline()
+  return table.unpack(result, 1, result.n)
+end
+
+function sandbox.xpcall(...)
+  local result = table.pack(xpcall(...))
+  checkDeadline()
+  return table.unpack(result, 1, result.n)
+end
+
 -------------------------------------------------------------------------------
 
 function sandbox.os.shutdown()
@@ -215,13 +228,13 @@ function sandbox.os.reboot()
 end
 
 function sandbox.os.signal(name, timeout)
-  local waitUntil = os.clock() + (type(timeout) == "number" and timeout or math.huge)
-  while os.clock() < waitUntil do
-    local signal = table.pack(coroutine.yield(waitUntil - os.clock()))
+  local waitUntil = os.uptime() + (type(timeout) == "number" and timeout or math.huge)
+  repeat
+    local signal = table.pack(coroutine.yield(waitUntil - os.uptime()))
     if signal.n > 0 and (name == signal[1] or name == nil) then
       return table.unpack(signal, 1, signal.n)
     end
-  end
+  until os.uptime() >= waitUntil
 end
 
 -------------------------------------------------------------------------------
diff --git a/assets/opencomputers/lua/rom/api/event.lua b/assets/opencomputers/lua/rom/api/event.lua
index 13b9b7f9a..16d438fb2 100644
--- a/assets/opencomputers/lua/rom/api/event.lua
+++ b/assets/opencomputers/lua/rom/api/event.lua
@@ -55,7 +55,7 @@ function event.fire(name, ...)
   end
   local elapsed = {}
   for id, info in pairs(timers) do
-    if info.after < os.clock() then
+    if info.after < os.uptime() then
       table.insert(elapsed, info.callback)
       timers[id] = nil
     end
@@ -70,7 +70,7 @@ end
 
 function event.timer(timeout, callback)
   local id = #timers + 1
-  timers[id] = {after = os.clock() + timeout, callback = callback}
+  timers[id] = {after = os.uptime() + timeout, callback = callback}
   return id
 end
 
@@ -98,7 +98,7 @@ end
 function coroutine.sleep(seconds)
   seconds = seconds or math.huge
   checkArg(1, seconds, "number")
-  local target = os.clock() + seconds
+  local target = os.uptime() + seconds
   repeat
     local closest = target
     for _, info in pairs(timers) do
@@ -106,6 +106,6 @@ function coroutine.sleep(seconds)
         closest = info.after
       end
     end
-    event.fire(os.signal(nil, closest - os.clock()))
-  until os.clock() >= target
+    event.fire(os.signal(nil, closest - os.uptime()))
+  until os.uptime() >= target
 end
diff --git a/assets/opencomputers/lua/rom/api/term.lua b/assets/opencomputers/lua/rom/api/term.lua
index cbf2a8a86..51344b5f9 100644
--- a/assets/opencomputers/lua/rom/api/term.lua
+++ b/assets/opencomputers/lua/rom/api/term.lua
@@ -1,18 +1,20 @@
-local gpu = nil
-local gpuAddress, screenAddress, keyboardAddress = false, false, false
+local gpuAddress, screenAddress, keyboardAddress = nil, nil, nil
 local width, height = 0, 0
 local cursorX, cursorY = 1, 1
 local cursorBlink = nil
 
-local function bindIfPossible()
-  if gpuAddress and screenAddress then
-    if not gpu then
-      gpu = driver.gpu.bind(gpuAddress, screenAddress)
-      width, height = gpu.getResolution()
-      event.fire("term_available")
-    end
-  elseif gpu then
-    gpu, width, height = nil, 0, 0
+local function rebind(gpu, screen)
+  if gpu == gpuAddress and screen == screenAddress then
+    return
+  end
+  local oldGpu, oldScreen = gpuAddress, screenAddress
+  gpuAddress, screenAddress = gpu, screen
+  if gpu and screen then
+    driver.gpu.bind(gpuAddress, screenAddress)
+    width, height = driver.gpu.resolution(gpuAddress)
+    event.fire("term_available")
+  elseif gpuAddress and screenAddress then
+    width, height = 0, 0
     event.fire("term_unavailable")
   end
 end
@@ -21,16 +23,20 @@ end
 
 term = {}
 
+function term.available()
+  return gpuAddress and screenAddress
+end
+
 function term.clear()
-  if gpu then
-    gpu.fill(1, 1, width, height, " ")
+  if term.available() then
+    driver.gpu.fill(term.gpu(), 1, 1, width, height, " ")
   end
   cursorX, cursorY = 1, 1
 end
 
 function term.clearLine()
-  if gpu then
-    gpu.fill(1, cursorY, width, 1, " ")
+  if term.available() then
+    driver.gpu.fill(term.gpu(), 1, cursorY, width, 1, " ")
   end
   cursorX = 1
 end
@@ -47,10 +53,10 @@ function term.cursorBlink(enabled)
   if type(enabled) == "boolean" and enabled ~= (cursorBlink ~= nil) then
     local function toggleBlink()
       cursorBlink.state = not cursorBlink.state
-      if gpu then
+      if term.available() then
          -- 0x2588 is a solid block.
         local char = cursorBlink.state and string.char(0x2588) or " "
-        gpu.set(cursorX, cursorY, char)
+        driver.gpu.set(term.gpu(), cursorX, cursorY, char)
       end
     end
     if enabled then
@@ -67,25 +73,29 @@ function term.cursorBlink(enabled)
   return cursorBlink ~= nil
 end
 
-function term.gpu(address)
-  if address ~= nil and ({boolean=true, string=true})[type(address)] then
-    gpuAddress = address
-    bindIfPossible()
+function term.gpu(...)
+  local args = table.pack(...)
+  if args.n > 0 then
+    checkArg(1, args[1], "string", "nil")
+    rebind(args[1], term.screen())
   end
-  return gpuAddress, gpu
+  return gpuAddress
 end
 
-function term.keyboard(address)
-  if address ~= nil and ({boolean=true, string=true})[type(address)] then
-    keyboardAddress = address
+function term.keyboard(...)
+  local args = table.pack(...)
+  if args.n > 0 then
+    checkArg(1, args[1], "string", "nil")
+    keyboardAddress = args[1]
   end
   return keyboardAddress
 end
 
-function term.screen(address)
-  if address ~= nil and ({boolean=true, string=true})[type(address)] then
-    screenAddress = address
-    bindIfPossible()
+function term.screen(...)
+  local args = table.pack(...)
+  if args.n > 0 then
+    checkArg(1, args[1], "string", "nil")
+    rebind(term.gpu(), args[1])
   end
   return screenAddress
 end
@@ -97,7 +107,7 @@ end
 function term.write(value, wrap)
   value = tostring(value)
   local w, h = width, height
-  if value:len() == 0 or not gpu or w < 1 or h < 1 then
+  if value:len() == 0 or not term.available() or w < 1 or h < 1 then
     return
   end
   value = value:gsub("\t", "  ")
@@ -107,8 +117,8 @@ function term.write(value, wrap)
       cursorY = cursorY + 1
     end
     if cursorY > h then
-      gpu.copy(1, 1, w, h, 0, -1)
-      gpu.fill(1, h, w, 1, " ")
+      driver.gpu.copy(term.gpu(), 1, 1, w, h, 0, -1)
+      driver.gpu.fill(term.gpu(), 1, h, w, 1, " ")
       cursorY = h
     end
   end
@@ -116,12 +126,12 @@ function term.write(value, wrap)
     while wrap and line:len() > w - cursorX + 1 do
       local partial = line:sub(1, w - cursorX + 1)
       line = line:sub(partial:len() + 1)
-      gpu.set(cursorX, cursorY, partial)
+      driver.gpu.set(term.gpu(), cursorX, cursorY, partial)
       cursorX = cursorX + partial:len()
       checkCursor()
     end
     if line:len() > 0 then
-      gpu.set(cursorX, cursorY, line)
+      driver.gpu.set(term.gpu(), cursorX, cursorY, line)
       cursorX = cursorX + line:len()
     end
     if nl:len() == 1 then
@@ -136,34 +146,34 @@ end
 
 event.listen("component_added", function(_, address)
   local type = component.type(address)
-  if type == "gpu" and not gpuAddress then
+  if type == "gpu" and not term.gpu() then
     term.gpu(address)
-  elseif type == "screen" and not screenAddress then
+  elseif type == "screen" and not term.screen() then
     term.screen(address)
-  elseif type == "keyboard" and not keyboardAddress then
+  elseif type == "keyboard" and not term.keyboard() then
     term.keyboard(address)
   end
 end)
 
 event.listen("component_removed", function(_, address)
-  if gpuAddress == address then
-    term.gpu(false)
+  if term.gpu() == address then
+    term.gpu(nil)
     for address in component.list() do
       if component.type(address) == "gpu" then
         term.gpu(address)
         return
       end
     end
-  elseif screenAddress == address then
-    term.screen(false)
+  elseif term.screen() == address then
+    term.screen(nil)
     for address in component.list() do
       if component.type(address) == "screen" then
         term.screen(address)
         return
       end
     end
-  elseif keyboardAddress == address then
-    term.keyboard(false)
+  elseif term.keyboard() == address then
+    term.keyboard(nil)
     for address in component.list() do
       if component.type(address) == "keyboard" then
         term.keyboard(address)
@@ -174,7 +184,7 @@ event.listen("component_removed", function(_, address)
 end)
 
 event.listen("screen_resized", function(_, address, w, h)
-  if address == screenAddress then
+  if term.screen() == address then
     width = w
     height = h
   end
diff --git a/assets/opencomputers/lua/rom/bin/sh.lua b/assets/opencomputers/lua/rom/bin/sh.lua
index 2208d6db8..1d2cf9120 100644
--- a/assets/opencomputers/lua/rom/bin/sh.lua
+++ b/assets/opencomputers/lua/rom/bin/sh.lua
@@ -6,15 +6,15 @@ local isRunning = false
 local function onKeyDown(_, address, char, code)
   if isRunning then return end -- ignore events while running a command
   if address ~= term.keyboard() then return end
-  local _, gpu = term.gpu()
-  if not gpu then return end
+  if not term.available() then return end
   local x, y = term.cursor()
+  local w, h = term.size()
   local keys = driver.keyboard.keys
   if code == keys.back then
     if command:len() == 0 then return end
     command = command:sub(1, -2)
     term.cursor(command:len() + 3, y) -- from leading "> "
-    gpu.set(x - 1, y, "  ") -- overwrite cursor blink
+    driver.gpu.set(term.gpu(), x - 1, y, "  ") -- overwrite cursor blink
   elseif code == keys.enter then
     if command:len() == 0 then return end
     term.cursorBlink(false)
@@ -39,7 +39,7 @@ local function onKeyDown(_, address, char, code)
     term.cursorBlink(true)
   elseif code == keys.up then
     command = lastCommand
-    gpu.fill(3, y, screenWidth, 1, " ")
+    driver.gpu.fill(term.gpu(), 3, y, w, 1, " ")
     term.cursor(3, y)
     term.write(command)
     term.cursor(command:len() + 3, y)
diff --git a/li/cil/oc/server/component/Computer.scala b/li/cil/oc/server/component/Computer.scala
index ba232ac55..656942035 100644
--- a/li/cil/oc/server/component/Computer.scala
+++ b/li/cil/oc/server/component/Computer.scala
@@ -70,16 +70,22 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
 
   // ----------------------------------------------------------------------- //
 
-  private var timeStarted = 0L // Game-world time for os.clock().
+  private var timeStarted = 0L // Game-world time [ms] for os.uptime().
 
   private var worldTime = 0L // Game-world time for os.time().
 
-  private var lastUpdate = 0L // Real-world time for pause detection.
+  private var lastUpdate = 0L // Real-world time [ms] for pause detection.
 
-  private var sleepUntil = Double.PositiveInfinity // Real-world time.
+  private var cpuTime = 0L // Pseudo-real-world time [ns] for os.clock().
+
+  private var cpuStart = 0L // Pseudo-real-world time [ns] for os.clock().
+
+  private var sleepUntil = Double.PositiveInfinity // Real-world time [ms].
 
   private var wasRunning = false // To signal stops synchronously.
 
+  private var message: Option[String] = None // For error messages.
+
   // ----------------------------------------------------------------------- //
 
   def recomputeMemory() = if (lua != null)
@@ -154,10 +160,19 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
     worldTime = owner.world.getWorldInfo.getWorldTotalTime
 
     // Signal stops to the network. This is used to close file handles, for example.
-    if (wasRunning && !isRunning)
+    if (wasRunning && !isRunning) {
       owner.network.foreach(_.sendToVisible(owner, "computer.stopped"))
+      owner.network.foreach(_.sendToNeighbors(owner, "gpu.fill", 1.0, 1.0, Double.PositiveInfinity, Double.PositiveInfinity, " ".getBytes("UTF-8")))
+    }
     wasRunning = isRunning
 
+    if (message.isDefined) owner.network.foreach(network => {
+      for ((line, row) <- message.get.lines.zipWithIndex) {
+        network.sendToNeighbors(owner, "gpu.set", 1.0, 1.0 + row, line.getBytes("UTF-8"))
+      }
+      message = None
+    })
+
     // Check if we should switch states.
     stateMonitor.synchronized(state match {
       // Computer is rebooting.
@@ -204,16 +219,14 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
             // This can happen if we run out of memory while converting a Java
             // exception to a string (which we have to do to avoid keeping
             // userdata on the stack, which cannot be persisted).
-            OpenComputers.log.warning("Out of memory!") // TODO remove this when we have a component that can display crash messages
-            //owner.network.foreach(_.sendToVisible(owner, "computer.crashed", "not enough memory"))
+            message = Some("not enough memory")
             close()
           case e: java.lang.Error if e.getMessage == "not enough memory" =>
-            OpenComputers.log.warning("Out of memory!") // TODO remove this when we have a component that can display crash messages
-            // TODO get this to the world as a computer.crashed message. problem: synchronizing it.
-            //owner.network.foreach(_.sendToVisible(owner, "computer.crashed", "not enough memory"))
+            message = Some("not enough memory")
             close()
           case e: Throwable => {
             OpenComputers.log.log(Level.WARNING, "Faulty Lua implementation for synchronized calls.", e)
+            message = Some("protocol error")
             close()
           }
         }
@@ -273,6 +286,9 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
         rom.foreach(_.load(nbt.getCompoundTag("rom")))
         kernelMemory = nbt.getInteger("kernelMemory")
         timeStarted = nbt.getLong("timeStarted")
+        cpuTime = nbt.getLong("cpuTime")
+        if (nbt.hasKey("message"))
+          message = Some(nbt.getString("message"))
 
         // Clean up some after we're done and limit memory again.
         lua.gc(LuaState.GcAction.COLLECT, 0)
@@ -353,6 +369,9 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
       nbt.setCompoundTag("rom", romNbt)
       nbt.setInteger("kernelMemory", kernelMemory)
       nbt.setLong("timeStarted", timeStarted)
+      nbt.setLong("cpuTime", cpuTime)
+      if (message.isDefined)
+        nbt.setString("message", message.get)
     }
     catch {
       case e: Throwable => {
@@ -417,12 +436,9 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
       lua.getGlobal("os")
 
       // Custom os.clock() implementation returning the time the computer has
-      // been running, instead of the native library...
+      // been actively running, instead of the native library...
       lua.pushScalaFunction(lua => {
-        // World time is in ticks, and each second has 20 ticks. Since we
-        // want os.clock() to return real seconds, though, we'll divide it
-        // accordingly.
-        lua.pushNumber((worldTime - timeStarted) / 20.0)
+        lua.pushNumber((cpuTime + (System.nanoTime() - cpuStart)) * 10e-10)
         1
       })
       lua.setField(-2, "clock")
@@ -438,6 +454,16 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
       })
       lua.setField(-2, "time")
 
+      // The time the computer has been running, as opposed to the CPU time.
+      lua.pushScalaFunction(lua => {
+        // World time is in ticks, and each second has 20 ticks. Since we
+        // want os.uptime() to return real seconds, though, we'll divide it
+        // accordingly.
+        lua.pushNumber((worldTime - timeStarted) / 20.0)
+        1
+      })
+      lua.setField(-2, "uptime")
+
       // Allow the system to read how much memory it uses and has available.
       lua.pushScalaFunction(lua => {
         lua.pushInteger(lua.getTotalMemory - kernelMemory)
@@ -592,7 +618,7 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
       // underlying system (which may change across releases). Add some buffer
       // to avoid the init script eating up all the rest immediately.
       lua.gc(LuaState.GcAction.COLLECT, 0)
-      kernelMemory = (lua.getTotalMemory - lua.getFreeMemory) + 2048
+      kernelMemory = (lua.getTotalMemory - lua.getFreeMemory) + 8 * 1024
       recomputeMemory()
 
       // Clear any left-over signals from a previous run.
@@ -621,6 +647,8 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
       kernelMemory = 0
       signals.clear()
       timeStarted = 0
+      cpuTime = 0
+      cpuStart = 0
       future = None
       sleepUntil = Long.MaxValue
 
@@ -628,6 +656,8 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
       owner.markAsChanged()
     })
 
+  // ----------------------------------------------------------------------- //
+
   private def execute(value: Computer.State.Value) {
     assert(future.isEmpty)
     sleepUntil = Long.MaxValue
@@ -666,6 +696,7 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
 
     try {
       // Resume the Lua state and remember the number of results we get.
+      cpuStart = System.nanoTime()
       val results = if (callReturn) {
         // If we were doing a synchronized call, continue where we left off.
         assert(lua.getTop == 2)
@@ -685,6 +716,7 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
           lua.resume(1, 1 + signal.args.length)
         }
       }
+      cpuTime += System.nanoTime() - cpuStart
 
       // Check if the kernel is still alive.
       stateMonitor.synchronized(if (lua.status(1) == LuaState.YIELD) {
@@ -746,9 +778,7 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
         else {
           // This can trigger another out of memory error if the original
           // error was an out of memory error.
-          OpenComputers.log.warning("Computer crashed.\n" + lua.toString(3)) // TODO remove this when we have a component that can display crash messages
-          // TODO get this to the world as a computer.crashed message. problem: synchronizing it.
-          //owner.network.sendToAll(owner, "computer.crashed", lua.toString(3))
+          message = Some(lua.toString(3))
         }
         close()
       })
@@ -756,16 +786,13 @@ class Computer(val owner: Computer.Environment) extends Persistable with Runnabl
     catch {
       case e: LuaRuntimeException =>
         OpenComputers.log.warning("Kernel crashed. This is a bug!\n" + e.toString + "\tat " + e.getLuaStackTrace.mkString("\n\tat "))
+        message = Some("kernel panic")
         close()
       case e: LuaMemoryAllocationException =>
-        OpenComputers.log.warning("Out of memory!") // TODO remove this when we have a component that can display crash messages
-        // TODO get this to the world as a computer.crashed message. problem: synchronizing it.
-        //owner.network.sendToAll(owner, "computer.crashed", "not enough memory")
+        message = Some("not enough memory")
         close()
       case e: java.lang.Error if e.getMessage == "not enough memory" =>
-        OpenComputers.log.warning("Out of memory!") // TODO remove this when we have a component that can display crash messages
-        // TODO get this to the world as a computer.crashed message. problem: synchronizing it.
-        //owner.network.sendToAll(owner, "computer.crashed", "not enough memory")
+        message = Some("not enough memory")
         close()
     }
   }
diff --git a/li/cil/oc/server/component/GraphicsCard.scala b/li/cil/oc/server/component/GraphicsCard.scala
index 90957c414..246a6d82e 100644
--- a/li/cil/oc/server/component/GraphicsCard.scala
+++ b/li/cil/oc/server/component/GraphicsCard.scala
@@ -1,10 +1,16 @@
 package li.cil.oc.server.component
 
 import li.cil.oc.api.network.{Node, Visibility, Message}
+import li.cil.oc.common.component.ScreenEnvironment
+import net.minecraft.nbt.NBTTagCompound
 
 class GraphicsCard extends Node {
   val supportedResolutions = List(List(40, 24), List(80, 24))
 
+  private var screen: Option[String] = None
+
+  // ----------------------------------------------------------------------- //
+
   override def name = "gpu"
 
   override def visibility = Visibility.Neighbors
@@ -12,32 +18,66 @@ class GraphicsCard extends Node {
   override def receive(message: Message) = {
     super.receive(message)
     message.data match {
-      case Array(screen: Array[Byte], w: Double, h: Double) if message.name == "gpu.resolution=" =>
+      case Array(address: Array[Byte]) if message.name == "gpu.bind" =>
+        network.fold(None: Option[Array[Any]])(network => {
+          network.node(new String(address, "UTF-8")) match {
+            case None => Some(Array(Unit, "invalid address"))
+            case Some(node: ScreenEnvironment) =>
+              screen = node.address
+              Some(Array(true.asInstanceOf[Any]))
+            case _ => Some(Array(Unit, "not a screen"))
+          }
+        })
+      case Array() if message.name == "network.disconnect" && message.source.address == screen => screen = None; None
+      case Array(w: Double, h: Double) if message.name == "gpu.resolution=" =>
         if (supportedResolutions.contains((w.toInt, h.toInt)))
-          trySend(new String(screen, "UTF-8"), "screen.resolution=", w.toInt, h.toInt)
+          trySend("screen.resolution=", w.toInt, h.toInt)
         else
           Some(Array(Unit, "unsupported resolution"))
-      case Array(screen: Array[Byte]) if message.name == "gpu.resolution" =>
-        trySend(new String(screen, "UTF-8"), "screen.resolution")
-      case Array(screen: Array[Byte]) if message.name == "gpu.resolutions" =>
-        trySend(new String(screen, "UTF-8"), "screen.resolutions") match {
-          case Some(Array(resolutions@_*)) =>
-            Some(Array(supportedResolutions.intersect(resolutions): _*))
-          case _ => None
-        }
-      case Array(screen: Array[Byte], x: Double, y: Double, value: Array[Byte]) if message.name == "gpu.set" =>
-        trySend(new String(screen, "UTF-8"), "screen.set", x.toInt - 1, y.toInt - 1, new String(value, "UTF-8"))
-      case Array(screen: Array[Byte], x: Double, y: Double, w: Double, h: Double, value: Array[Byte]) if message.name == "gpu.fill" =>
+      case Array() if message.name == "gpu.resolution" => trySend("screen.resolution")
+      case Array() if message.name == "gpu.resolutions" => trySend("screen.resolutions") match {
+        case Some(Array(resolutions@_*)) =>
+          Some(Array(supportedResolutions.intersect(resolutions): _*))
+        case _ => None
+      }
+      case Array(x: Double, y: Double, value: Array[Byte]) if message.name == "gpu.set" =>
+        trySend("screen.set", x.toInt - 1, y.toInt - 1, new String(value, "UTF-8"))
+      case Array(x: Double, y: Double, w: Double, h: Double, value: Array[Byte]) if message.name == "gpu.fill" =>
         val s = new String(value, "UTF-8")
         if (s.length == 1)
-          trySend(new String(screen, "UTF-8"), "screen.fill", x.toInt - 1, y.toInt - 1, w.toInt, h.toInt, s.charAt(0))
+          trySend("screen.fill", x.toInt - 1, y.toInt - 1, w.toInt, h.toInt, s.charAt(0))
         else
           Some(Array(Unit, "invalid fill value"))
-      case Array(screen: Array[Byte], x: Double, y: Double, w: Double, h: Double, tx: Double, ty: Double) if message.name == "gpu.copy" =>
-        trySend(new String(screen, "UTF-8"), "screen.copy", x.toInt - 1, y.toInt - 1, w.toInt, h.toInt, tx.toInt, ty.toInt)
+      case Array(x: Double, y: Double, w: Double, h: Double, tx: Double, ty: Double) if message.name == "gpu.copy" =>
+        trySend("screen.copy", x.toInt - 1, y.toInt - 1, w.toInt, h.toInt, tx.toInt, ty.toInt)
       case _ => None
     }
   }
 
-  private def trySend(target: String, name: String, data: Any*) = network.fold(None: Option[Array[Any]])(net => net.sendToAddress(this, target, name, data: _*))
+  override protected def onDisconnect() = {
+    super.onDisconnect()
+    screen = None
+  }
+
+  override def load(nbt: NBTTagCompound) = {
+    super.load(nbt)
+    if (nbt.hasKey("screen"))
+      screen = Some(nbt.getString("screen"))
+  }
+
+  override def save(nbt: NBTTagCompound) = {
+    super.save(nbt)
+    if (screen.isDefined)
+      nbt.setString("screen", screen.get)
+  }
+
+  // ----------------------------------------------------------------------- //
+
+  private def trySend(name: String, data: Any*): Option[Array[Any]] =
+    screen match {
+      case None => Some(Array(Unit, "no screen"))
+      case Some(screenAddress) => network.fold(None: Option[Array[Any]])(net => {
+        net.sendToAddress(this, screenAddress, name, data: _*)
+      })
+    }
 }
\ No newline at end of file
diff --git a/li/cil/oc/server/network/Network.scala b/li/cil/oc/server/network/Network.scala
index d836b4c32..7f9309e3b 100644
--- a/li/cil/oc/server/network/Network.scala
+++ b/li/cil/oc/server/network/Network.scala
@@ -26,6 +26,8 @@ class Network private(private val addressedNodes: mutable.Map[String, Network.No
   addressedNodes.values.foreach(_.data.network = Some(this))
   unaddressedNodes.foreach(_.data.network = Some(this))
 
+  // ----------------------------------------------------------------------- //
+
   override def connect(nodeA: api.network.Node, nodeB: api.network.Node) = {
     val containsA = contains(nodeA)
     val containsB = contains(nodeB)
@@ -104,6 +106,8 @@ class Network private(private val addressedNodes: mutable.Map[String, Network.No
     }
   }
 
+  // ----------------------------------------------------------------------- //
+
   override def node(address: String) = addressedNodes.get(address) match {
     case Some(node) => Some(node.data)
     case _ => None
@@ -130,6 +134,8 @@ class Network private(private val addressedNodes: mutable.Map[String, Network.No
       }
   }
 
+  // ----------------------------------------------------------------------- //
+
   override def sendToAddress(source: api.network.Node, target: String, name: String, data: Any*) = {
     if (source.network.isEmpty || source.network.get != this)
       throw new IllegalArgumentException("Source node must be in this network.")
@@ -157,6 +163,8 @@ class Network private(private val addressedNodes: mutable.Map[String, Network.No
     else None
   }
 
+  // ----------------------------------------------------------------------- //
+
   private def contains(node: api.network.Node) = (node.address match {
     case None => unaddressedNodes.find(_.data == node)
     case Some(address) => addressedNodes.get(address)
@@ -306,6 +314,18 @@ object Network extends api.detail.NetworkAPI {
       }
     }
 
+  private def getNetworkNode(world: IBlockAccess, x: Int, y: Int, z: Int): Option[TileEntity with api.network.Node] =
+    Option(Block.blocksList(world.getBlockId(x, y, z))) match {
+      case Some(block) if block.hasTileEntity(world.getBlockMetadata(x, y, z)) =>
+        world.getBlockTileEntity(x, y, z) match {
+          case tileEntity: TileEntity with api.network.Node => Some(tileEntity)
+          case _ => None
+        }
+      case _ => None
+    }
+
+  // ----------------------------------------------------------------------- //
+
   @ForgeSubscribe
   def onChunkUnload(e: ChunkEvent.Unload) =
     onUnload(e.world, e.getChunk.chunkTileEntityMap.values.asScala.map(_.asInstanceOf[TileEntity]))
@@ -326,15 +346,7 @@ object Network extends api.detail.NetworkAPI {
     tileEntities.foreach(t => joinOrCreateNetwork(w, t.xCoord, t.yCoord, t.zCoord))
   }
 
-  private def getNetworkNode(world: IBlockAccess, x: Int, y: Int, z: Int): Option[TileEntity with api.network.Node] =
-    Option(Block.blocksList(world.getBlockId(x, y, z))) match {
-      case Some(block) if block.hasTileEntity(world.getBlockMetadata(x, y, z)) =>
-        world.getBlockTileEntity(x, y, z) match {
-          case tileEntity: TileEntity with api.network.Node => Some(tileEntity)
-          case _ => None
-        }
-      case _ => None
-    }
+  // ----------------------------------------------------------------------- //
 
   private class Node(val data: api.network.Node) {
     val edges = ArrayBuffer.empty[Edge]
@@ -382,6 +394,8 @@ object Network extends api.detail.NetworkAPI {
     }) filter (_.nonEmpty) map (_.get)
   }
 
+  // ----------------------------------------------------------------------- //
+
   private class Message(@BeanProperty val source: api.network.Node,
                         @BeanProperty val name: String,
                         @BeanProperty val data: Array[Any] = Array()) extends api.network.Message {