Implement pop

include/shmemq.h

@@ -25,6 +25,8 @@ typedef enum ShmemqError {
 
     SHMEMQ_ERROR_INVALID_NAME = 1,
 
+    SHMEMQ_ERROR_BUG_POP_END_ON_EMPTY_QUEUE = 50,
+
     SHMEMQ_ERROR_FAILED_MALLOC     = 255,
     SHMEMQ_ERROR_FAILED_SHM_OPEN   = 254,
     SHMEMQ_ERROR_FAILED_FTRUNCATE  = 253,
@@ -79,6 +81,10 @@ ShmemqFrame shmemq_push_start(Shmemq shmemq);
 
 void shmemq_push_end(Shmemq shmemq, size_t data_size, ShmemqError *error_ptr);
 
+ShmemqFrame shmemq_pop_start(Shmemq shmemq);
+
+void shmemq_pop_end(Shmemq shmemq, ShmemqError *error_ptr);
+
 #ifdef __cplusplus
 }
 #endif

src/main.c

@@ -193,3 +193,37 @@ void shmemq_push_end(
         shmemq->buffer->header.write_frame_index = new_write_frame_index;
     }
 }
+
+ShmemqFrame shmemq_pop_start(const Shmemq shmemq)
+{
+    return &shmemq->buffer->frames[shmemq->buffer->header.read_frame_index];
+}
+
+void shmemq_pop_end(const Shmemq shmemq, ShmemqError *const error_ptr)
+{
+    if (error_ptr) *error_ptr = SHMEMQ_ERROR_NONE;
+
+    if (
+        shmemq->buffer->header.read_frame_index ==
+        shmemq->buffer->header.write_frame_index
+    ) {
+        *error_ptr = SHMEMQ_ERROR_BUG_POP_END_ON_EMPTY_QUEUE;
+        return;
+    }
+
+    const ShmemqFrame frame =
+        &shmemq->buffer->frames[shmemq->buffer->header.read_frame_index];
+
+    if (
+        shmemq->buffer->header.read_frame_index <
+        shmemq->buffer->header.write_frame_index ||
+        frame->header.message_frames_count != 0
+    ) {
+        shmemq->buffer->header.read_frame_index +=
+            frame->header.message_frames_count;
+
+        return;
+    }
+
+    shmemq->buffer->header.read_frame_index = 0;
+}

tests/test_main.c

@@ -117,6 +117,48 @@ int main()
         ) == 0
     );
 
+    frame = shmemq_pop_start(&consumer_shmemq);
+
+    assert(frame == &consumer_shmemq.buffer->frames[0]);
+    assert(producer_shmemq->buffer->header.read_frame_index == 0);
+    assert(frame->header.message_frames_count == 1);
+    assert(frame->data[0] == 123);
+    assert(frame->data[1] == 0);
+    assert(frame->data[2] == 0);
+    assert(frame->data[3] == 0);
+
+    shmemq_pop_end(&consumer_shmemq, &error);
+
+    assert(error == SHMEMQ_ERROR_NONE);
+    assert(producer_shmemq->buffer->header.read_frame_index == 1);
+
+    frame = shmemq_pop_start(&consumer_shmemq);
+
+    assert(frame == &consumer_shmemq.buffer->frames[1]);
+    assert(producer_shmemq->buffer->header.read_frame_index == 1);
+    assert(frame->header.message_frames_count == 1);
+    assert(frame->data[0] == 200);
+    assert(frame->data[1] == 1);
+    assert(frame->data[2] == 0);
+    assert(frame->data[3] == 0);
+
+    shmemq_pop_end(&consumer_shmemq, &error);
+
+    assert(error == SHMEMQ_ERROR_NONE);
+    assert(producer_shmemq->buffer->header.read_frame_index == 2);
+
+    frame = shmemq_pop_start(&consumer_shmemq);
+
+    assert(frame == &consumer_shmemq.buffer->frames[2]);
+    assert(producer_shmemq->buffer->header.read_frame_index == 2);
+    assert(frame->header.message_frames_count == 2);
+    assert(strcmp((char*)frame->data, hello_world_str) == 0);
+
+    shmemq_pop_end(&consumer_shmemq, &error);
+
+    assert(error == SHMEMQ_ERROR_NONE);
+    assert(producer_shmemq->buffer->header.read_frame_index == 4);
+
     shmemq_finish(&consumer_shmemq, &error);
     assert(error == SHMEMQ_ERROR_NONE);