Add __io_lock() and __io_unlock() functions to lock io functions

printf.c

@@ -95,6 +95,12 @@
 #define PRINTF_SUPPORT_PTRDIFF_T
 #endif
 
+// add lock and unlock functions to protect io operations
+// default: deactivated
+#ifdef PRINTF_ENABLE_LOCK
+#define PRINTF_IO_LOCK
+#endif
+
 ///////////////////////////////////////////////////////////////////////////////
 
 // internal flag definitions
@@ -861,11 +867,17 @@ static int _vsnprintf(out_fct_type out, char* buffer, const size_t maxlen, const
 
 int printf_(const char* format, ...)
 {
+#if defined(PRINTF_IO_LOCK)
+  __io_lock();
+#endif
   va_list va;
   va_start(va, format);
   char buffer[1];
   const int ret = _vsnprintf(_out_char, buffer, (size_t)-1, format, va);
   va_end(va);
+#if defined(PRINTF_IO_LOCK)
+  __io_unlock();
+#endif
   return ret;
 }
 

printf.h

@@ -40,6 +40,21 @@
 extern "C" {
 #endif
 
+/**
+ * Lock the printf to avoid collision when multiple threads/cores try to output strings/characters.
+ * This function can implement a mutex, semaphore or whatever lock.
+ *
+ * \note PRINTF_ENABLE_LOCK should be defined in order to activate lock function.
+ */
+void __io_lock();
+
+/**
+ * Unlock the printf, release the lock, semaphore or mutex used to lock printf.
+ * This function releases the mutex, semaphore or whatever lock used previously.
+ *
+ * \note PRINTF_ENABLE_LOCK should be defined in order to activate unlock function.
+ */
+void __io_unlock();
 
 /**
  * Output a character to a custom device like UART, used by the printf() function