add a Lock, LockGuard and printThreadInfo

* `Lock`: trivial wrapper for FreeRTOS binary semaphores
* `LockGuard`: RAII wrapper for using `Lock`
* `printThreadInfo`: helper for showing which core/FreeRTOS task we are
  running under

src/lock.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <FreeRTOS/FreeRTOS.h>
+#include <FreeRTOS/semphr.h>
+
+namespace meshtastic
+{
+
+// Simple wrapper around FreeRTOS API for implementing a mutex lock.
+class Lock
+{
+  public:
+    Lock();
+
+    Lock(const Lock&) = delete;
+    Lock& operator=(const Lock&) = delete;
+
+    /// Locks the lock.
+    //
+    // Must not be called from an ISR.
+    void lock();
+
+    // Unlocks the lock.
+    //
+    // Must not be called from an ISR.
+    void unlock();
+
+  private:
+    SemaphoreHandle_t handle;
+};
+
+// RAII lock guard.
+class LockGuard
+{
+  public:
+    LockGuard(Lock *lock);
+    ~LockGuard();
+
+    LockGuard(const LockGuard&) = delete;
+    LockGuard& operator=(const LockGuard&) = delete;
+
+  private:
+    Lock* lock;
+};
+
+
+} // namespace meshtastic