native implementation

binding.gyp

@@ -0,0 +1,12 @@
+{
+  'targets': [
+    {
+      'target_name': 'toobusy',
+      'include_dirs': [
+      ],
+      'sources': [
+        'toobusy.cc',
+      ]
+    }
+  ]
+}

examples/http.js

@@ -7,9 +7,15 @@ http.createServer(function (req, res) {
     return res.end("I'm a bit busy right now, come back later\n");
   }
   // we're not too busy!  let's process a request!
-  var i = 0;
-  while (i < 1e6) i++;
+  process.nextTick(function() {
+    var i = 0;
+    while (i < 1e6) i++;
+    process.nextTick(function() {
+      var j = 0;
+      while (j < 1e6) j++;
 
-  res.writeHead(200, {'Content-Type': 'text/plain'});
-  res.end('I counted to ' + i + '\n');
+      res.writeHead(200, {'Content-Type': 'text/plain'});
+      res.end('I counted to ' + i + '\n');
+    });
+  });
 }).listen(3000, '127.0.0.1', 1024);

index.js

@@ -1,58 +1,3 @@
-const events = require('events');
-
-// constants
-const eventsEmitted = [ 'busy', 'normal' ];
-const POLL_PERIOD_MS = 500;
-var HIGH_WATER_MARK_MS = 100;
-
-// state
-var polling = false;
-var timer = null;
-
-// api
-module.exports.stop = function() {
-  stopPolling();
-};
-
-// implementation
-function startPolling() {
-  if (polling) return;
-  polling = true;
-  checkState();
-}
-
-function stopPolling() {
-  if (!polling) return;
-  clearTimeout(timer);
-  timer = null;
-  polling = false;
-}
-
-var lastMark = null;
-var lagging = false;
-function checkState() {
-  if (!polling) return;
-  if (lastMark) {
-    var lag = new Date() - lastMark - POLL_PERIOD_MS;
-
-    // have we transitioned across the high water mark?
-    if (!lagging && lag > HIGH_WATER_MARK_MS) {
-      lagging = lag;
-    } else if (lagging && lag < HIGH_WATER_MARK_MS) {
-      lagging = null;
-    }
-  }
-  lastMark = new Date();
-  timer = setTimeout(checkState, POLL_PERIOD_MS);
-}
-
-module.exports = function() {
-  startPolling();
-  if (lagging) return lagging;
-  var curLag = new Date() - lastMark - POLL_PERIOD_MS;
-  if (lastMark && curLag > HIGH_WATER_MARK_MS)
-    return curLag;
-  return null;
-};
-
-module.exports.shutdown = stopPolling;
+var bindings = require('bindings')('toobusy.node')
+module.exports = bindings.toobusy;
+module.exports.shutdown = bindings.shutdown;

toobusy.cc

@@ -0,0 +1,63 @@
+#include <v8.h>
+#include <node.h>
+#include <uv.h>
+#include <stdlib.h>
+#include <sys/time.h>
+
+using namespace v8;
+
+static const unsigned int POLL_PERIOD_MS = 500;
+static const unsigned int HIGH_WATER_MARK_MS = 50;
+static const unsigned int AVG_DECAY_FACTOR = 3;
+
+//static uv_idle_t s_idler;
+static uv_timer_t s_timer;
+static uint64_t s_currentLag;
+static uint64_t s_lastMark;
+static uint64_t s_avgCalls;
+static uint64_t s_calls;
+
+Handle<Value> TooBusy(const Arguments& args) {
+    bool block = false;
+    if (s_currentLag > HIGH_WATER_MARK_MS) {
+        // probabilistically block 2x as many requests as we would need
+        // to in order to catch up.
+        double pctToBlock = ((s_currentLag - HIGH_WATER_MARK_MS) /
+                             (double) HIGH_WATER_MARK_MS) * 100.0;
+        double r = (rand() / (double) RAND_MAX) * 100.0;
+        if (r < pctToBlock) block = true;
+    }
+    s_calls++;
+    return Boolean::New(block);
+}
+
+Handle<Value> ShutDown(const Arguments& args) {
+    uv_timer_stop(&s_timer);
+    return Undefined();
+}
+
+static void every_second(uv_timer_t* handle, int status)
+{
+    uint64_t now = uv_hrtime();
+
+    s_avgCalls = (s_calls + (s_avgCalls * (AVG_DECAY_FACTOR-1))) /
+        AVG_DECAY_FACTOR;
+    s_calls = 0;
+
+    if (s_lastMark > 0) {
+        uint64_t lag = ((now - s_lastMark) / 1000000);
+        lag = (lag < POLL_PERIOD_MS) ? 0 : lag - POLL_PERIOD_MS;
+        s_currentLag = (lag + (s_currentLag * (AVG_DECAY_FACTOR-1))) /
+            AVG_DECAY_FACTOR;
+    }
+    s_lastMark = now;
+};
+
+extern "C" void init(Handle<Object> target) {
+    HandleScope scope;
+
+    target->Set(String::New("toobusy"), FunctionTemplate::New(TooBusy)->GetFunction());
+    target->Set(String::New("shutdown"), FunctionTemplate::New(ShutDown)->GetFunction());
+    uv_timer_init(uv_default_loop(), &s_timer);
+    uv_timer_start(&s_timer, every_second, POLL_PERIOD_MS, POLL_PERIOD_MS);
+};