Add support for static mutexes

hal/api/AnalogIn.h

@@ -118,7 +118,7 @@ class AnalogIn {
     }
 
     analogin_t _adc;
-    static PlatformMutex _mutex;
+    static PlatformMutexStatic _mutex;
 };
 
 } // namespace mbed

hal/api/FileBase.h

@@ -65,7 +65,7 @@ class FileBase {
     /* disallow copy constructor and assignment operators */
 private:
     static FileBase *_head;
-    static PlatformMutex _mutex;
+    static PlatformMutexStatic _mutex;
 
     FileBase   *_next;
     const char * const _name;

hal/api/I2C.h

@@ -181,7 +181,7 @@ class I2C {
     i2c_t _i2c;
     static I2C  *_owner;
     int         _hz;
-    static PlatformMutex _mutex;
+    static PlatformMutexStatic _mutex;
 };
 
 } // namespace mbed

hal/api/platform.h

@@ -21,6 +21,7 @@
 #include "device.h"
 #include "PinNames.h"
 #include "PeripheralNames.h"
+#include "critical.h"
 
 #include <cstddef>
 #include <cstdlib>
@@ -54,4 +55,55 @@ class PlatformMutex {
 
 #endif
 
+/** The static version of a PlatformMutex
+ *
+ * This class must only be used in a static context -
+ * this class must never be allocated or created on the
+ * stack.
+ *
+ * This class is lazily initialized on first use.
+ * This class is a POD type so if it is not used it will
+ * be garbage collected.
+ */
+struct PlatformMutexStatic {
+    PlatformMutex* _mutex;
+
+    void _init() {
+        PlatformMutex* current = _mutex;
+        PlatformMutex* new_mutex;
+
+        if (NULL == current) {
+            bool done = false;
+            new_mutex = new PlatformMutex;
+            while (!done) {
+                done = core_util_atomic_cas_ptr((void**)&_mutex, (void**)&current, (void*)new_mutex);
+                if (current != NULL) {
+                    // Mutex was created on another thread first
+                    // so delete ours
+                    delete new_mutex;
+                    break;
+                }
+            }
+        }
+    }
+
+    /** Wait until this Mutex becomes available.
+     */
+    void lock() {
+        if (NULL == _mutex) {
+            _init();
+        }
+        _mutex->lock();
+    }
+
+    /** Unlock the mutex that has previously been locked by the same thread
+     */
+    void unlock() {
+        if (NULL == _mutex) {
+            _init();
+        }
+        _mutex->unlock();
+    }
+};
+
 #endif

hal/common/AnalogIn.cpp

@@ -22,7 +22,7 @@
 
 namespace mbed {
 
-PlatformMutex AnalogIn::_mutex;
+PlatformMutexStatic AnalogIn::_mutex;
 
 };
 

hal/common/FileBase.cpp

@@ -18,7 +18,7 @@
 namespace mbed {
 
 FileBase *FileBase::_head = NULL;
-PlatformMutex FileBase::_mutex;
+PlatformMutexStatic FileBase::_mutex;
 
 FileBase::FileBase(const char *name, PathType t) : _next(NULL),
                                                    _name(name),

hal/common/I2C.cpp

@@ -20,7 +20,7 @@
 namespace mbed {
 
 I2C *I2C::_owner = NULL;
-PlatformMutex I2C::_mutex;
+PlatformMutexStatic I2C::_mutex;
 
 I2C::I2C(PinName sda, PinName scl) :
 #if DEVICE_I2C_ASYNCH

hal/common/retarget.cpp

@@ -72,7 +72,7 @@ extern const char __stderr_name[] = "/stderr";
  * (or rather index+3, as filehandles 0-2 are stdin/out/err).
  */
 static FileHandle *filehandles[OPEN_MAX];
-static PlatformMutex filehandle_mutex;
+static PlatformMutexStatic filehandle_mutex;
 
 FileHandle::~FileHandle() {
     filehandle_mutex.lock();