Add test "prod_reaches_buffer_end"

.gitignore

@@ -37,3 +37,4 @@
 /examples/raw_receiver
 /examples/raw_sender
 /tests/test_main
+/tests/test_prod_reaches_buffer_end

Makefile.am

@@ -9,7 +9,8 @@ AM_CFLAGS = \
 lib_LIBRARIES = libshmemq.a
 
 TESTS = \
-	tests/test_main
+	tests/test_main \
+	tests/test_prod_reaches_buffer_end
 
 noinst_PROGRAMS = \
 	$(TESTS) \
@@ -29,3 +30,7 @@ examples_raw_sender_SOURCES = \
 tests_test_main_SOURCES = \
 	$(libshmemq_a_SOURCES) \
 	tests/test_main.c
+
+tests_test_prod_reaches_buffer_end_SOURCES = \
+	$(libshmemq_a_SOURCES) \
+	tests/test_prod_reaches_buffer_end.c

include/shmemq.h

@@ -28,6 +28,7 @@ typedef enum ShmemqError {
 
     // Bugs in user code.
     SHMEMQ_ERROR_BUG_POP_END_ON_EMPTY_QUEUE = 50,
+    SHMEMQ_ERROR_BUG_PUSH_END_ON_FULL_QUEUE = 51,
 
     // Failed system calls.
     SHMEMQ_ERROR_FAILED_MALLOC     = 100,

src/main.c

@@ -144,6 +144,13 @@ void shmemq_init(
 
 ShmemqFrame shmemq_push_start(const Shmemq shmemq)
 {
+    if (
+        shmemq->buffer->header.write_frame_index >=
+        shmemq->buffer->header.frames_count
+    ) {
+        return NULL;
+    }
+
     const ShmemqFrame low_frame  = &shmemq->buffer->frames[0];
     const ShmemqFrame high_frame = &shmemq->buffer->frames[
         shmemq->buffer->header.write_frame_index
@@ -167,6 +174,14 @@ void shmemq_push_end(
 ) {
     if (error_ptr) *error_ptr = SHMEMQ_ERROR_NONE;
 
+    if (
+        shmemq->buffer->header.write_frame_index >=
+        shmemq->buffer->header.frames_count
+    ) {
+        if (error_ptr) *error_ptr = SHMEMQ_ERROR_BUG_PUSH_END_ON_FULL_QUEUE;
+        return;
+    }
+
     const ShmemqFrame frame =
         &shmemq->buffer->frames[shmemq->buffer->header.write_frame_index];
 
@@ -186,7 +201,10 @@ void shmemq_push_end(
         shmemq->buffer->header.write_frame_index +
         frame->header.message_frames_count;
 
-    if (new_write_frame_index >= shmemq->buffer->header.frames_count) {
+    if (
+        new_write_frame_index >= shmemq->buffer->header.frames_count &&
+        shmemq->buffer->header.read_frame_index > 0
+    ) {
         shmemq->buffer->header.write_frame_index = 0;
     }
     else {

tests/test_prod_reaches_buffer_end.c

@@ -0,0 +1,39 @@
+#include <shmemq.h>
+
+#include <assert.h>
+
+static const char name[] = "/foobar";
+
+int main()
+{
+    ShmemqError error;
+
+    const Shmemq consumer = shmemq_new(name, true, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    const Shmemq producer = shmemq_new(name, false, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    for (unsigned i = 0; i < 100; ++i) {
+        const ShmemqFrame frame = shmemq_push_start(producer);
+        assert(frame != NULL);
+
+        *(unsigned*)frame->data = i;
+
+        shmemq_push_end(producer, sizeof(unsigned), &error);
+        assert(error == SHMEMQ_ERROR_NONE);
+    }
+
+    assert(shmemq_push_start(producer) == NULL);
+
+    shmemq_push_end(producer, sizeof(unsigned), &error);
+    assert(error == SHMEMQ_ERROR_BUG_PUSH_END_ON_FULL_QUEUE);
+
+    shmemq_delete(consumer, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    shmemq_delete(producer, &error);
+    assert(error == SHMEMQ_ERROR_NONE);
+
+    return 0;
+}