3 files changed, 122 insertions, 1 deletions
diff --git a/src/core/lib/iomgr/network_status_tracker.c b/src/core/lib/iomgr/network_status_tracker.c
index b4bb7e3cf7..a5ca9ed2c3 100644
--- a/src/core/lib/iomgr/network_status_tracker.c
+++ b/src/core/lib/iomgr/network_status_tracker.c
@@ -46,7 +46,7 @@ static gpr_mu g_endpoint_mutex;
 void grpc_network_status_shutdown(void) {
   if (head != NULL) {
     gpr_log(GPR_ERROR,
-            "Memory leaked as all network endpoints were not shut down");
+            "Memory leaked as not all network endpoints were shut down");
   }
   gpr_mu_destroy(&g_endpoint_mutex);
 }
diff --git a/src/core/lib/transport/pid_controller.c b/src/core/lib/transport/pid_controller.c
new file mode 100644
index 0000000000..3cef225d4b
--- /dev/null
+++ b/src/core/lib/transport/pid_controller.c
@@ -0,0 +1,57 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/transport/pid_controller.h"
+
+void grpc_pid_controller_init(grpc_pid_controller *pid_controller,
+                              double gain_p, double gain_i, double gain_d) {
+  pid_controller->gain_p = gain_p;
+  pid_controller->gain_i = gain_i;
+  pid_controller->gain_d = gain_d;
+  grpc_pid_controller_reset(pid_controller);
+}
+
+void grpc_pid_controller_reset(grpc_pid_controller *pid_controller) {
+  pid_controller->last_error = 0.0;
+  pid_controller->error_integral = 0.0;
+}
+
+double grpc_pid_controller_update(grpc_pid_controller *pid_controller,
+                                  double error, double dt) {
+  pid_controller->error_integral += error * dt;
+  double diff_error = (error - pid_controller->last_error) / dt;
+  pid_controller->last_error = error;
+  return dt * (pid_controller->gain_p * error +
+               pid_controller->gain_i * pid_controller->error_integral +
+               pid_controller->gain_d * diff_error);
+}
diff --git a/src/core/lib/transport/pid_controller.h b/src/core/lib/transport/pid_controller.h
new file mode 100644
index 0000000000..059b5b0834
--- /dev/null
+++ b/src/core/lib/transport/pid_controller.h
@@ -0,0 +1,64 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_TRANSPORT_PID_CONTROLLER_H
+#define GRPC_CORE_LIB_TRANSPORT_PID_CONTROLLER_H
+
+/* \file Simple PID controller.
+   Implements a proportional-integral-derivative controller.
+   Used when we want to iteratively control a variable to converge some other
+   observed value to a 'set-point'.
+   Gains can be set to adjust sensitivity to current error (p), the integral
+   of error (i), and the derivative of error (d). */
+
+typedef struct {
+  double gain_p;
+  double gain_i;
+  double gain_d;
+  double last_error;
+  double error_integral;
+} grpc_pid_controller;
+
+/** Initialize the controller */
+void grpc_pid_controller_init(grpc_pid_controller *pid_controller,
+                              double gain_p, double gain_i, double gain_d);
+
+/** Reset the controller: useful when things have changed significantly */
+void grpc_pid_controller_reset(grpc_pid_controller *pid_controller);
+
+/** Update the controller: given a current error estimate, and the time since
+    the last update, returns a delta to the control value */
+double grpc_pid_controller_update(grpc_pid_controller *pid_controller,
+                                  double error, double dt);
+
+#endif