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diff --git a/butl/process-details b/butl/process-details
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+// file      : butl/process-details -*- C++ -*-
+// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUTL_PROCESS_DETAILS
+#define BUTL_PROCESS_DETAILS
+
+#include <mutex>
+
+#include <butl/ft/shared_mutex>
+#if defined(__cpp_lib_shared_mutex) || defined(__cpp_lib_shared_timed_mutex)
+#  include <shared_mutex>
+#endif
+
+namespace butl
+{
+#if   defined(__cpp_lib_shared_mutex)
+  using shared_mutex = std::shared_mutex;
+  using ulock        = std::unique_lock<shared_mutex>;
+  using slock        = std::shared_lock<shared_mutex>;
+#elif defined(__cpp_lib_shared_timed_mutex)
+  using shared_mutex = std::shared_timed_mutex;
+  using ulock        = std::unique_lock<shared_mutex>;
+  using slock        = std::shared_lock<shared_mutex>;
+#else
+  // Because we have this fallback, we need to be careful not to create
+  // multiple shared locks in the same thread.
+  //
+  struct shared_mutex: std::mutex
+  {
+    using mutex::mutex;
+
+    void lock_shared     () { lock ();     }
+    void try_lock_shared () { try_lock (); }
+    void unlock_shared   () { unlock ();   }
+  };
+
+  using ulock        = std::unique_lock<shared_mutex>;
+  using slock        = ulock;
+#endif
+
+  // Mutex that is acquired to make a sequence of operations atomic in regards
+  // to child process spawning. Must be aquired for exclusive access for child
+  // process startup, and for shared access otherwise. Defined in process.cxx.
+  //
+  extern shared_mutex process_spawn_mutex;
+}
+
+#endif // BUTL_PROCESS_DETAILS