Implemented thread service support.

Added a wsrep::thread_service interface to allow application to
inject instrumented thread, mutex and condition variable implementation
for provider.

The interface is defined in include/wsrep/thread_service.hpp.
Sample implementation is provided in dbsim/db_threads.[h|c]pp.

This patch will also clean up some remaining dependencies to
wsrep-API compilation units so that the dependency to wsrep-API
is header only. This will extending the provider support to
later wsrep-API versions.

include/wsrep/thread_service.hpp

@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2019 Codership Oy <info@codership.com>
+ *
+ * This file is part of wsrep-lib.
+ *
+ * Wsrep-lib 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, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * Wsrep-lib 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 wsrep-lib.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+
+/** @file thread_service.hpp
+ *
+ * Service interface for threads and synchronization primitives.
+ * The purpose of this interface is to provider provider implementations
+ * means to integrate with application thread implementation.
+ *
+ * Interface is designed to resemble POSIX threads, mutexes and
+ * condition variables.
+ */
+
+#include <cstddef> // size_t
+#include "compiler.hpp"
+
+struct timespec;
+struct sched_param;
+
+namespace wsrep
+{
+
+    class thread_service
+    {
+    public:
+
+        virtual ~thread_service() { }
+        class thread_key { };
+        class thread { };
+        class mutex_key { };
+        class mutex { };
+        class cond_key { };
+        class cond { };
+
+        /**
+         * Method will be called before library side thread
+         * service initialization.
+         */
+        virtual int before_init() = 0;
+
+        /**
+         * Method will be called after library side thread service
+         * has been initialized.
+         */
+        virtual int after_init() = 0;
+
+        /* Thread */
+        virtual const thread_key* create_thread_key(const char* name) WSREP_NOEXCEPT
+            = 0;
+        virtual int create_thread(const thread_key*, thread**,
+                                  void* (*fn)(void*), void*) WSREP_NOEXCEPT
+            = 0;
+        virtual int detach(thread*) WSREP_NOEXCEPT = 0;
+        virtual int equal(thread*, thread*) WSREP_NOEXCEPT = 0;
+        WSREP_NORETURN virtual void exit(thread*, void* retval) WSREP_NOEXCEPT = 0;
+        virtual int join(thread*, void** retval) WSREP_NOEXCEPT = 0;
+        virtual thread* self() WSREP_NOEXCEPT = 0;
+        virtual int setschedparam(thread*, int,
+                                  const struct sched_param*) WSREP_NOEXCEPT
+            = 0;
+        virtual int getschedparam(thread*, int*, struct sched_param*) WSREP_NOEXCEPT
+            = 0;
+
+        /* Mutex */
+        virtual const mutex_key* create_mutex_key(const char* name) WSREP_NOEXCEPT
+            = 0;
+        virtual mutex* init_mutex(const mutex_key*, void*, size_t) WSREP_NOEXCEPT = 0;
+        virtual int destroy(mutex*) WSREP_NOEXCEPT = 0;
+        virtual int lock(mutex*) WSREP_NOEXCEPT = 0;
+        virtual int trylock(mutex*) WSREP_NOEXCEPT = 0;
+        virtual int unlock(mutex*) WSREP_NOEXCEPT = 0;
+
+        /* Condition variable */
+        virtual const cond_key* create_cond_key(const char* name) WSREP_NOEXCEPT = 0;
+        virtual cond* init_cond(const cond_key*, void*, size_t) WSREP_NOEXCEPT = 0;
+        virtual int destroy(cond*) WSREP_NOEXCEPT = 0;
+        virtual int wait(cond*, mutex*) WSREP_NOEXCEPT = 0;
+        virtual int timedwait(cond*, mutex*, const struct timespec*) WSREP_NOEXCEPT
+            = 0;
+        virtual int signal(cond*) WSREP_NOEXCEPT = 0;
+        virtual int broadcast(cond*) WSREP_NOEXCEPT = 0;
+    };
+} // namespace wsrep