MultiFM: Support reconnecting decoder to FIFO

If a decoder crashes or terminates spuriously, we now support
reconnecting that decoder to the MultiFM output pipe, withot having to
restart MultiFM from scratch.

multifm/demod.c

@@ -130,8 +130,21 @@ aresult_t demod_thread_process(struct demod_thread *dthr, struct sample_buf *sbu
         /* x. Write out the resulting PCM samples */
         if (0 > write(dthr->fifo_fd, dthr->pcm_out_buf, dthr->nr_pcm_samples * sizeof(int16_t))) {
             int errnum = errno;
-            PANIC("Failed to write %zu bytes to the output fifo. Reason: %s (%d)", sizeof(int16_t) * dthr->nr_pcm_samples,
-                    strerror(errnum), errnum);
+            if (errnum == EPIPE) {
+                if (0 == dthr->nr_dropped_samples) {
+                    MFM_MSG(SEV_WARNING, "FIFO-REMOTE-END-DISCONNECTED", "Remote end of FIFO disconnected. "
+                            "Until a process picks up the FIFO, we're dropping samples.");
+                }
+                dthr->nr_dropped_samples += dthr->nr_pcm_samples;
+            } else {
+                PANIC("Failed to write %zu bytes to the output fifo. Reason: %s (%d)",
+                        sizeof(int16_t) * dthr->nr_pcm_samples,
+                        strerror(errnum), errnum);
+            }
+        } else if (0 != dthr->nr_dropped_samples) {
+            MFM_MSG(SEV_WARNING, "FIFO-RESUMED", "Remote FIFO end reconnected. Dropped %zu samples in the interim.",
+                    dthr->nr_dropped_samples);
+            dthr->nr_dropped_samples = 0;
         }
 
         TSL_BUG_IF_FAILED(direct_fir_can_process(&dthr->fir, &can_process, NULL));

multifm/demod.h

@@ -94,6 +94,11 @@ struct demod_thread {
      */
     size_t total_nr_pcm_samples;
 
+    /**
+     * Number of samples dropped on the floor
+     */
+    size_t nr_dropped_samples;
+
     /**
      * Number of FM signal samples available
      */

multifm/multifm.c

@@ -22,16 +22,17 @@
  */
 
 #include <multifm/multifm.h>
-#if HAVE_RTLSDR
+
+#ifdef HAVE_RTLSDR
 #include <multifm/rtl_sdr_if.h>
 #include <rtl-sdr.h>
 #endif /* HAVE_RTLSDR */
 
-#if HAVE_DESPAIRSPY
+#ifdef HAVE_DESPAIRSPY
 #include <multifm/airspy_if.h>
 #endif
 
-#if HAVE_UHD
+#ifdef HAVE_UHD
 #include <multifm/uhd_if.h>
 #endif
 
@@ -126,21 +127,21 @@ int main(int argc, const char *argv[])
 
     /* Prepare the RTL-SDR thread and demod threads */
     if (!strncmp(dev_type, "rtlsdr", 6)) {
-#if HAVE_RTLSDR
+#ifdef HAVE_RTLSDR
         TSL_BUG_IF_FAILED(rtl_sdr_worker_thread_new(&rx_thr, cfg));
 #else
         MFM_MSG(SEV_FATAL, "RTLSDR-NOT-SUPPORTED", "RTL-SDR devices are not supported by this build.");
         goto done;
 #endif
     } else if (!strncmp(dev_type, "airspy", 6)) {
-#if HAVE_DESPAIRSPY
+#ifdef HAVE_DESPAIRSPY
         TSL_BUG_IF_FAILED(airspy_worker_thread_new(&rx_thr, cfg));
 #else
         MFM_MSG(SEV_FATAL, "AIRSPY-NOT-SUPPORTED", "Airspy devices are not supported by this build.");
         goto done;
 #endif
     } else if (!strncmp(dev_type, "usrp", 4)) {
-#if HAVE_UHD
+#ifdef HAVE_UHD
         TSL_BUG_IF_FAILED(uhd_worker_thread_new(&rx_thr, cfg));
 #else
         MFM_MSG(SEV_FATAL, "USRP-NOT-SUPPORTED", "USRP devices are not supported by this build.");

multifm/receiver.c

@@ -55,7 +55,10 @@ aresult_t receiver_sample_buf_alloc(struct receiver *rx, struct sample_buf **pbu
 
     /* Allocate an output buffer */
     if (FAILED(ret = frame_alloc(rx->samp_alloc, (void **)&sbuf))) {
-        MFM_MSG(SEV_INFO, "NO-SAMPLE-BUFFER", "Out of sample buffers.");
+        if (0 == rx->nr_samp_buf_alloc_fails) {
+            MFM_MSG(SEV_INFO, "NO-SAMPLE-BUFFER", "There are no available sample buffers, dropping received samples.");
+        }
+        rx->nr_samp_buf_alloc_fails++;
         goto done;
     }
 

multifm/receiver.h

@@ -32,6 +32,11 @@ struct receiver {
      */
     size_t nr_demod_threads;
 
+    /**
+     * Number of failed sample buffer allocations
+     */
+    size_t nr_samp_buf_alloc_fails;
+
     /**
      * Frame allocator of sample buffers
      */