Merge branch 'mutex' into 'master'

Mutex

:snail::dash: :zap::zap:

Basic mutex implementation, uses a try to lock model, where unsuccessfully obtaining a lock returns a 1, but does not hang.

See merge request !17

src/mutex.c

+#include "mutex.h"
+
+mutex mutex_create()
+{
+    mutex m;
+    m.lock_var=0;
+    m.value=0;
+    m.thread_id=0;
+    return m;
+}
+
+uint32_t mutex_lock(mutex m)
+{
+    asm volatile
+    (
+     "mov $1, %%eax;       \
+      xchg %[lock], %%eax; \
+      mov %%eax, %[value]"
+     :[value] "=r" (m.value)
+     :[lock] "r" (m.lock_var)
+    );
+    return m.value;
+}
+
+uint32_t mutex_unlock(mutex m)
+{
+    asm volatile
+    (
+     "mov $0, %%eax;       \
+      xchg %[lock], %%eax; \
+      mov %%eax, %[value]"
+     :[value] "=r" (m.value)
+     :[lock] "r" (m.lock_var)
+    );
+    return m.value;
+}

src/mutex.h

+#ifndef _MUTEX_INC
+#define _MUTEX_INC
+
+#include <stdint.h>
+
+typedef struct
+{
+    uint32_t lock_var;
+    uint32_t value;
+    uint32_t thread_id;
+}__attribute__((packed)) mutex;
+
+mutex mutex_create();
+uint32_t mutex_lock(mutex m);
+uint32_t mutex_unlock(mutex m);
+
+#endif