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+/*****************************************************************************
+
+Copyright (c) 2014, Oracle and/or its affiliates. All Rights Reserved.
+
+This program is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free Software
+Foundation; version 2 of the License.
+
+This program is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA
+
+*****************************************************************************/
+
+/**************************************************//**
+@file include/os0once.h
+A class that aids executing a given function exactly once in a multi-threaded
+environment.
+
+Created Feb 20, 2014 Vasil Dimov
+*******************************************************/
+
+#ifndef os0once_h
+#define os0once_h
+
+#include "univ.i"
+
+#include "os0sync.h"
+#include "ut0ut.h"
+
+/** Execute a given function exactly once in a multi-threaded environment
+or wait for the function to be executed by another thread.
+
+Example usage:
+First the user must create a control variable of type os_once::state_t and
+assign it os_once::NEVER_DONE.
+Then the user must pass this variable, together with a function to be
+executed to os_once::do_or_wait_for_done().
+
+Multiple threads can call os_once::do_or_wait_for_done() simultaneously with
+the same (os_once::state_t) control variable. The provided function will be
+called exactly once and when os_once::do_or_wait_for_done() returns then this
+function has completed execution, by this or another thread. In other words
+os_once::do_or_wait_for_done() will either execute the provided function or
+will wait for its execution to complete if it is already called by another
+thread or will do nothing if the function has already completed its execution
+earlier.
+
+This mimics pthread_once(3), but unfortunatelly pthread_once(3) does not
+support passing arguments to the init_routine() function. We should use
+std::call_once() when we start compiling with C++11 enabled. */
+class os_once {
+public:
+	/** Control variables' state type */
+	typedef ib_uint32_t	state_t;
+
+	/** Not yet executed. */
+	static const state_t	NEVER_DONE = 0;
+
+	/** Currently being executed by this or another thread. */
+	static const state_t	IN_PROGRESS = 1;
+
+	/** Finished execution. */
+	static const state_t	DONE = 2;
+
+#ifdef HAVE_ATOMIC_BUILTINS
+	/** Call a given function or wait its execution to complete if it is
+	already called by another thread.
+	@param[in,out]	state		control variable
+	@param[in]	do_func		function to call
+	@param[in,out]	do_func_arg	an argument to pass to do_func(). */
+	static
+	void
+	do_or_wait_for_done(
+		volatile state_t*	state,
+		void			(*do_func)(void*),
+		void*			do_func_arg)
+	{
+		/* Avoid calling os_compare_and_swap_uint32() in the most
+		common case. */
+		if (*state == DONE) {
+			return;
+		}
+
+		if (os_compare_and_swap_uint32(state,
+					       NEVER_DONE, IN_PROGRESS)) {
+			/* We are the first. Call the function. */
+
+			do_func(do_func_arg);
+
+			const bool	swapped = os_compare_and_swap_uint32(
+				state, IN_PROGRESS, DONE);
+
+			ut_a(swapped);
+		} else {
+			/* The state is not NEVER_DONE, so either it is
+			IN_PROGRESS (somebody is calling the function right
+			now or DONE (it has already been called and completed).
+			Wait for it to become DONE. */
+			for (;;) {
+				const state_t	s = *state;
+
+				switch (s) {
+				case DONE:
+					return;
+				case IN_PROGRESS:
+					break;
+				case NEVER_DONE:
+					/* fall through */
+				default:
+					ut_error;
+				}
+
+				UT_RELAX_CPU();
+			}
+		}
+	}
+#endif /* HAVE_ATOMIC_BUILTINS */
+};
+
+#endif /* os0once_h */