Fix intermittent underruns after a restart

When using UHD without synchronous=1:
After a modulator restart, the input ZMQ buffer is nearly empty, and
the modulator actually gets blocked by the ThreadsafeQueue. This is
visible by looking at the time deltas printed in the debugging code.

This commit adds a minimal form of prebuffering (10 ETI frames) to the
ZeroMQ input, and removes the useless minimum required size for the
ThreadsafeQueue.

In synchronous=1, the issue is not visible because the TIST defines the
time to transmit, which will cause the ZMQ buffer to fill.

6 files changed, 72 insertions, 23 deletions

diff --git a/src/FIRFilter.h b/src/FIRFilter.h
index 05627d4..751be91 100644
--- a/src/FIRFilter.h
+++ b/src/FIRFilter.h
@@ -31,7 +31,6 @@
 
 #include <boost/thread.hpp>
 #include <boost/shared_ptr.hpp>
-#include "ThreadsafeQueue.h"
 
 #include "RemoteControl.h"
 #include "ModCodec.h"
diff --git a/src/InputReader.h b/src/InputReader.h
index 37aa523..b262cc9 100644
--- a/src/InputReader.h
+++ b/src/InputReader.h
@@ -183,8 +183,7 @@ class InputZeroMQWorker
 class InputZeroMQReader : public InputReader
 {
     public:
-        InputZeroMQReader() :
-            in_messages_(10)
+        InputZeroMQReader()
         {
             workerdata_.in_messages = &in_messages_;
             workerdata_.running     = false;
diff --git a/src/InputZeroMQReader.cpp b/src/InputZeroMQReader.cpp
index 8706e1e..e95644a 100644
--- a/src/InputZeroMQReader.cpp
+++ b/src/InputZeroMQReader.cpp
@@ -41,6 +41,7 @@
 #include "porting.h"
 #include "InputReader.h"
 #include "PcDebug.h"
+#include "Utils.h"
 
 #define NUM_FRAMES_PER_ZMQ_MESSAGE 4
 /* A concatenation of four ETI frames,
@@ -86,7 +87,34 @@ int InputZeroMQReader::GetNextFrame(void* buffer)
     const size_t framesize = 6144;
 
     boost::shared_ptr<std::vector<uint8_t> > incoming;
-    in_messages_.wait_and_pop(incoming);
+
+    struct timespec time_before;
+    int time_before_ret = clock_gettime(CLOCK_MONOTONIC, &time_before);
+
+    /* Do some prebuffering because reads will happen in bursts
+     * (4 ETI frames in TM1) and we should make sure that
+     * we can serve the data required for a full transmission frame.
+     */
+    if (in_messages_.size() < 4) {
+        const size_t prebuffering = 10;
+        in_messages_.wait_and_pop(incoming, prebuffering);
+    }
+    else {
+        in_messages_.wait_and_pop(incoming);
+    }
+
+    struct timespec time_after;
+    int time_after_ret = clock_gettime(CLOCK_MONOTONIC, &time_after);
+
+    if (time_before_ret == 0 and time_after_ret == 0) {
+        etiLog.level(debug) << "ZMQ Time delta : " <<
+            timespecdiff_us(time_before, time_after) << " us, queue " <<
+            in_messages_.size();
+    }
+    else {
+        etiLog.level(error) << "ZMQ Time delta failed " <<
+            time_before_ret << " " << time_after_ret;
+    }
 
     if (! workerdata_.running) {
         throw zmq_input_overflow();
@@ -193,7 +221,7 @@ void InputZeroMQWorker::RecvProcess(struct InputZeroMQThreadData* workerdata)
             }
 
             if (queue_size < 5) {
-                etiLog.level(warn) << "ZeroMQ buffer low: " << queue_size << "elements !";
+                etiLog.level(warn) << "ZeroMQ buffer low: " << queue_size << " elements !";
             }
         }
     }
diff --git a/src/OutputUHD.cpp b/src/OutputUHD.cpp
index ad31be7..acc4271 100644
--- a/src/OutputUHD.cpp
+++ b/src/OutputUHD.cpp
@@ -31,6 +31,7 @@
 #include "PcDebug.h"
 #include "Log.h"
 #include "RemoteControl.h"
+#include "Utils.h"
 
 #include <boost/thread/future.hpp>
 
@@ -349,8 +350,24 @@ int OutputUHD::process(Buffer* dataIn, Buffer* dataOut)
                 " to " << dataIn->getLength();
             throw std::runtime_error("Non-constant input length!");
         }
+
+        struct timespec time_before;
+        int time_before_ret = clock_gettime(CLOCK_MONOTONIC, &time_before);
+
         mySyncBarrier.get()->wait();
 
+        struct timespec time_after;
+        int time_after_ret = clock_gettime(CLOCK_MONOTONIC, &time_after);
+
+        if (time_before_ret == 0 and time_after_ret == 0) {
+            etiLog.level(debug) << "Time delta : " <<
+                timespecdiff_us(time_before, time_after) << " us";
+        }
+        else {
+            etiLog.level(error) << "Time delta failed " <<
+                time_before_ret << " " << time_after_ret;
+        }
+
         if (!uwd.running) {
             worker.stop();
             first_run = true;
diff --git a/src/ThreadsafeQueue.h b/src/ThreadsafeQueue.h
index 78e9ef0..e5e83ef 100644
--- a/src/ThreadsafeQueue.h
+++ b/src/ThreadsafeQueue.h
@@ -38,25 +38,14 @@
  * that pushes elements into the queue, and one consumer that
  * retrieves the elements.
  *
- * The queue can make the consumer block until enough elements
- * are available.
+ * The queue can make the consumer block until an element
+ * is available.
  */
 
 template<typename T>
 class ThreadsafeQueue
 {
 public:
-    /* Create a new queue without any minimum required
-     * fill before it is possible to pop an element
-     */
-    ThreadsafeQueue() : the_required_size(1) {}
-
-    /* Create a queue where it has to contain at least
-     * required_size elements before pop is possible
-     */
-    ThreadsafeQueue(size_t required_size) : the_required_size(required_size) {
-    }
-
     /* Push one element into the queue, and notify another thread that
      * might be waiting.
      *
@@ -87,14 +76,14 @@ public:
 
     size_t size() const
     {
+        boost::mutex::scoped_lock lock(the_mutex);
         return the_queue.size();
     }
 
     bool try_pop(T& popped_value)
     {
         boost::mutex::scoped_lock lock(the_mutex);
-        if(the_queue.size() < the_required_size)
-        {
+        if (the_queue.empty()) {
             return false;
         }
 
@@ -103,10 +92,10 @@ public:
         return true;
     }
 
-    void wait_and_pop(T& popped_value)
+    void wait_and_pop(T& popped_value, size_t prebuffering = 1)
     {
         boost::mutex::scoped_lock lock(the_mutex);
-        while(the_queue.size() < the_required_size) {
+        while (the_queue.size() < prebuffering) {
             the_condition_variable.wait(lock);
         }
 
@@ -118,7 +107,6 @@ private:
     std::queue<T> the_queue;
     mutable boost::mutex the_mutex;
     boost::condition_variable the_condition_variable;
-    size_t the_required_size;
 };
 
 #endif
diff --git a/src/Utils.h b/src/Utils.h
index 7c3129c..f023646 100644
--- a/src/Utils.h
+++ b/src/Utils.h
@@ -35,10 +35,28 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <stdio.h>
+#include <time.h>
 
 void printUsage(char* progName);
 
 void printVersion(void);
 
+inline long timespecdiff_us(struct timespec& oldTime, struct timespec& time)
+{
+    long tv_sec;
+    long tv_nsec;
+    if (time.tv_nsec < oldTime.tv_nsec) {
+        tv_sec = time.tv_sec - 1 - oldTime.tv_sec;
+        tv_nsec = 1000000000L + time.tv_nsec - oldTime.tv_nsec;
+    }
+    else {
+        tv_sec = time.tv_sec - oldTime.tv_sec;
+        tv_nsec = time.tv_nsec - oldTime.tv_nsec;
+    }
+
+    return tv_sec * 1000 + tv_nsec / 1000;
+}
+
+
 #endif