1 files changed, 58 insertions, 0 deletions
diff --git a/src/lib/utils/thread_utils/rwlock.cpp b/src/lib/utils/thread_utils/rwlock.cpp
new file mode 100644
index 000000000..58500a83d
--- /dev/null
+++ b/src/lib/utils/thread_utils/rwlock.cpp
@@ -0,0 +1,58 @@
+/*
+* (C) 2019 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/internal/rwlock.h>
+
+namespace Botan {
+
+RWLock::RWLock() : m_state(0) {}
+
+void RWLock::lock()
+   {
+   std::unique_lock<std::mutex> lock(m_mutex);
+   while(m_state & is_writing)
+      m_gate1.wait(lock);
+   m_state |= is_writing;
+   while(m_state & readers_mask)
+      m_gate2.wait(lock);
+   }
+
+void RWLock::unlock()
+   {
+   std::unique_lock<std::mutex> lock(m_mutex);
+   m_state = 0;
+   m_gate1.notify_all();
+   }
+
+void RWLock::lock_shared()
+   {
+   std::unique_lock<std::mutex> lock(m_mutex);
+   while((m_state & is_writing) || (m_state & readers_mask) == readers_mask)
+      m_gate1.wait(lock);
+   const uint32_t num_readers = (m_state & readers_mask) + 1;
+   m_state &= ~readers_mask;
+   m_state |= num_readers;
+   }
+
+void RWLock::unlock_shared()
+   {
+   std::unique_lock<std::mutex> lock(m_mutex);
+   const uint32_t num_readers = (m_state & readers_mask) - 1;
+   m_state &= ~readers_mask;
+   m_state |= num_readers;
+   if(m_state & is_writing)
+      {
+      if(num_readers == 0)
+         m_gate2.notify_one();
+      }
+   else
+      {
+      if(num_readers == readers_mask - 1)
+         m_gate1.notify_one();
+      }
+   }
+
+}