Adds a simple class that watches an executor for being blocked. (#528)

src/utils/ExecutorWatchdog.hxx

@@ -0,0 +1,87 @@
+/** \copyright
+ * Copyright (c) 2021, Balazs Racz
+ * 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.
+ *
+ * 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 HOLDER 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.
+ *
+ * \file ExecutorWatchdog.hxx
+ *
+ * Watches an executor and prints a message if it was blocked.
+ *
+ * @author Balazs Racz
+ * @date 5 April 2021
+ */
+
+#ifndef _UTILS_EXECUTORWATCHDOG_HXX_
+#define _UTILS_EXECUTORWATCHDOG_HXX_
+
+#include "executor/StateFlow.hxx"
+#include "os/os.h"
+#include "utils/logging.h"
+
+/// This stateflow checks an executor every 50 msec. If the latency of a wakeup
+/// is more than 50 msec, then prints a warning of how long the executor was
+/// blocked.
+class ExecutorWatchdog : public StateFlowBase
+{
+public:
+    /// Constructor.
+    /// @param service defines which executor to watch.
+    ExecutorWatchdog(Service *service)
+        : StateFlowBase(service)
+    {
+        start_flow(STATE(take_stamp));
+    }
+
+private:
+    Action take_stamp()
+    {
+        lastTimeMsec_ = NSEC_TO_MSEC(os_get_time_monotonic());
+        return sleep_and_call(&timer_, MSEC_TO_NSEC(50), STATE(woken));
+    }
+
+    Action woken()
+    {
+        uint32_t new_time_msec = NSEC_TO_MSEC(os_get_time_monotonic());
+        auto diff = new_time_msec - lastTimeMsec_;
+        if (diff > 100)
+        {
+            LOG(WARNING, "[WARN] Executor was blocked for %d msec",
+                (int)(diff - 50));
+        }
+        if (++count_ > (5000 / 50))
+        {
+            count_ = 0;
+            LOG(INFO, "Watchdog alive.");
+        }
+        return call_immediately(STATE(take_stamp));
+    }
+
+    StateFlowTimer timer_ {this};
+    /// Timestamp when we last went to sleep.
+    uint32_t lastTimeMsec_ {0};
+    /// Counter that controls printing a heartbeat message that we are fine.
+    int count_ {0};
+};
+
+#endif // _UTILS_EXECUTORWATCHDOG_HXX_