From ff7a28ff59ddf164f4a0363bfafc038aba944d1c Mon Sep 17 00:00:00 2001
From: Silvano Seva <silseva@fastwebnet.it>
Date: Tue, 24 May 2022 10:10:18 +0200
Subject: [PATCH] RingBuffer class: implemented eraseElement() function,
 rewritten the pop() function in a cleaner way, fixed a bug in the pop()
 function causing the not_full condition variable to be never rised.

---
 openrtx/include/core/ringbuf.h | 53 ++++++++++++++++++++++++----------
 1 file changed, 38 insertions(+), 15 deletions(-)

diff --git a/openrtx/include/core/ringbuf.h b/openrtx/include/core/ringbuf.h
index 419e427b..77385e6b 100644
--- a/openrtx/include/core/ringbuf.h
+++ b/openrtx/include/core/ringbuf.h
@@ -108,25 +108,27 @@ public:
     {
         pthread_mutex_lock(&mutex);
 
-        if(numElements == 0)
+        if((numElements == 0) && (blocking == false))
         {
-            if(blocking)
-            {
-                while(numElements == 0)
-                {
-                    pthread_cond_wait(&not_empty, &mutex);
-                }
-            }
-            else
-            {
-                pthread_mutex_unlock(&mutex);
-                return false;
-            }
+            // No elements present and non-blocking call: unlock mutex and return
+            pthread_mutex_unlock(&mutex);
+            return false;
         }
 
-        elem         = data[readPos];
-        readPos      = (readPos + 1) % N;
+        // The call is blocking: wait until there is something into the queue
+        while(numElements == 0)
+        {
+            pthread_cond_wait(&not_empty, &mutex);
+        }
+
+        // At least one element present pop one.
+        elem    = data[readPos];
+        readPos = (readPos + 1) % N;
+
+        // Signal that the queue is no more full
+        if(numElements >= N) pthread_cond_signal(&not_full);
         numElements -= 1;
+
         pthread_mutex_unlock(&mutex);
 
         return true;
@@ -152,6 +154,27 @@ public:
         return numElements >= N;
     }
 
+    /**
+     * Discard one element from the buffer's tail, creating a new empty slot.
+     * In case the buffer is full calling this function unlocks the eventual
+     * threads waiting to push data.
+     */
+    void eraseElement()
+    {
+        // Nothing to erase
+        if(numElements == 0) return;
+
+        pthread_mutex_lock(&mutex);
+
+        // Chomp away one element just by advancing the read pointer.
+        readPos = (readPos + 1) % N;
+
+        if(numElements >= N) pthread_cond_signal(&not_full);
+        numElements -= 1;
+
+        pthread_mutex_unlock(&mutex);
+    }
+
 private:
 
     size_t readPos;      ///< Read pointer.