From ccc886a92551d1f55f5b9d65f07968361e77a25d Mon Sep 17 00:00:00 2001
From: Phillip Johnston <phillip@embeddedartistry.com>
Date: Mon, 1 Mar 2021 15:44:34 -0800
Subject: [PATCH] Add a threadsafe example implementation.

---
 .../circular_buffer_no_modulo_threadsafe.c    | 166 ++++++++++++++++++
 examples/c/meson.build                        |   9 +
 2 files changed, 175 insertions(+)
 create mode 100644 examples/c/circular_buffer/circular_buffer_no_modulo_threadsafe.c

diff --git a/examples/c/circular_buffer/circular_buffer_no_modulo_threadsafe.c b/examples/c/circular_buffer/circular_buffer_no_modulo_threadsafe.c
new file mode 100644
index 0000000..484662a
--- /dev/null
+++ b/examples/c/circular_buffer/circular_buffer_no_modulo_threadsafe.c
@@ -0,0 +1,166 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <assert.h>
+
+#include "circular_buffer.h"
+
+// The definition of our circular buffer structure is hidden from the user
+struct circular_buf_t {
+	uint8_t * buffer;
+	size_t head;
+	size_t tail;
+	size_t max; //of the buffer
+};
+
+#pragma mark - Private Functions -
+
+static void advance_pointer(cbuf_handle_t cbuf)
+{
+	assert(cbuf);
+
+	if(circular_buf_full(cbuf))
+    {
+    	if(++(cbuf->tail) == cbuf->max)
+    	{
+    		cbuf->tail = 0;
+    	}
+    }
+
+    if(++(cbuf->head) == cbuf->max)
+	{
+		cbuf->head = 0;
+	}
+}
+
+static void retreat_pointer(cbuf_handle_t cbuf)
+{
+	assert(cbuf);
+
+	if(++(cbuf->tail) == cbuf->max)
+	{
+		cbuf->tail = 0;
+	}
+}
+
+#pragma mark - APIs -
+
+cbuf_handle_t circular_buf_init(uint8_t* buffer, size_t size)
+{
+	assert(buffer && size);
+
+	cbuf_handle_t cbuf = malloc(sizeof(circular_buf_t));
+	assert(cbuf);
+
+	cbuf->buffer = buffer;
+	cbuf->max = size;
+	circular_buf_reset(cbuf);
+
+	assert(circular_buf_empty(cbuf));
+
+	return cbuf;
+}
+
+void circular_buf_free(cbuf_handle_t cbuf)
+{
+	assert(cbuf);
+	free(cbuf);
+}
+
+void circular_buf_reset(cbuf_handle_t cbuf)
+{
+    assert(cbuf);
+
+    cbuf->head = 0;
+    cbuf->tail = 0;
+}
+
+size_t circular_buf_size(cbuf_handle_t cbuf)
+{
+	assert(cbuf);
+
+	size_t size = cbuf->max;
+
+	if(!circular_buf_full(cbuf))
+	{
+		if(cbuf->head >= cbuf->tail)
+		{
+			size = (cbuf->head - cbuf->tail);
+		}
+		else
+		{
+			size = (cbuf->max + cbuf->head - cbuf->tail);
+		}
+
+	}
+
+	return size;
+}
+
+size_t circular_buf_capacity(cbuf_handle_t cbuf)
+{
+	assert(cbuf);
+
+	return cbuf->max;
+}
+
+void circular_buf_put(cbuf_handle_t cbuf, uint8_t data)
+{
+	assert(cbuf && cbuf->buffer);
+
+    cbuf->buffer[cbuf->head] = data;
+
+    advance_pointer(cbuf);
+}
+
+int circular_buf_put2(cbuf_handle_t cbuf, uint8_t data)
+{
+    int r = -1;
+
+    assert(cbuf && cbuf->buffer);
+
+    if(!circular_buf_full(cbuf))
+    {
+        cbuf->buffer[cbuf->head] = data;
+        advance_pointer(cbuf);
+        r = 0;
+    }
+
+    return r;
+}
+
+int circular_buf_get(cbuf_handle_t cbuf, uint8_t * data)
+{
+    assert(cbuf && data && cbuf->buffer);
+
+    int r = -1;
+
+    if(!circular_buf_empty(cbuf))
+    {
+        *data = cbuf->buffer[cbuf->tail];
+        retreat_pointer(cbuf);
+
+        r = 0;
+    }
+
+    return r;
+}
+
+bool circular_buf_empty(cbuf_handle_t cbuf)
+{
+	assert(cbuf);
+
+    return (!circular_buf_full(cbuf) && (cbuf->head == cbuf->tail));
+}
+
+bool circular_buf_full(circular_buf_t* cbuf)
+{
+	// We need to handle the wraparound case
+	size_t head = cbuf->head + 1;
+	if(head == cbuf->max)
+	{
+		head = 0;
+	}
+
+	return head == cbuf->tail;
+}
diff --git a/examples/c/meson.build b/examples/c/meson.build
index 15e7f01..8dc3f46 100644
--- a/examples/c/meson.build
+++ b/examples/c/meson.build
@@ -26,6 +26,15 @@ executable('circular_buffer_no_modulo',
 	c_args: '-DCOMPILE_AS_EXAMPLE'
 )
 
+executable('circular_buffer_no_modulo_threadsafe',
+	[
+		'circular_buffer_test.c',
+		'circular_buffer/circular_buffer_no_modulo_threadsafe.c'
+	],
+	include_directories: include_directories('circular_buffer'),
+	c_args: '-DCOMPILE_AS_EXAMPLE'
+)
+
 executable('malloc_aligned',
 	'malloc_aligned.c',
 	c_args: '-DCOMPILE_AS_EXAMPLE',