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+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#pragma once
+
+#include <isc/thread.h>
+
+/*! \file isc/trampoline_p.h
+ * \brief isc__trampoline: allows safe reuse of thread ID numbers.
+ *
+ * The 'isc_hp' hazard pointer API uses an internal thread ID
+ * variable ('tid_v') that is incremented for each new thread that uses
+ * hazard pointers. This thread ID is then used as an index into a global
+ * shared table of hazard pointer state.
+ *
+ * Since the thread ID is only incremented and never decremented, the
+ * table can overflow if threads are frequently created and destroyed.
+ *
+ * A trampoline is a thin wrapper around any function to be called from
+ * a newly launched thread. It maintains a table of thread IDs used by
+ * current and previous threads; when a thread is destroyed, its slot in
+ * the trampoline table becomes available, and the next thread to occupy
+ * that slot can use the same thread ID that its predecessor did.
+ *
+ * The trampoline table initially has space for 64 worker threads in
+ * addition to the main thread. If more threads than that are in
+ * concurrent use, the table is reallocated with twice as much space.
+ * (Note that the number of concurrent threads is currently capped at
+ * 128 by the queue and hazard pointer implementations.)
+ */
+
+typedef struct isc__trampoline isc__trampoline_t;
+
+void
+isc__trampoline_initialize(void);
+/*%<
+ * Initialize the thread trampoline internal structures, must be called only
+ * once as a library constructor (see lib/isc/lib.c).
+ */
+
+void
+isc__trampoline_shutdown(void);
+/*%<
+ * Destroy the thread trampoline internal structures, must be called only
+ * once as a library destructor (see lib/isc/lib.c).
+ */
+
+isc__trampoline_t *
+isc__trampoline_get(isc_threadfunc_t start_routine, isc_threadarg_t arg);
+/*%<
+ * Get a free thread trampoline structure and initialize it with
+ * start_routine and arg passed to start_routine.
+ *
+ * Requires:
+ *\li	'start_routine' is a valid non-NULL thread start_routine
+ */
+
+void
+isc__trampoline_attach(isc__trampoline_t *trampoline);
+void
+isc__trampoline_detach(isc__trampoline_t *trampoline);
+/*%<
+ * Attach/detach the trampoline to/from the current thread.
+ *
+ * Requires:
+ * \li  'trampoline' is a valid isc__trampoline_t
+ */
+
+isc_threadresult_t
+isc__trampoline_run(isc_threadarg_t arg);
+/*%<
+ * Run the thread trampoline, this will get passed to the actual
+ * pthread_create(), initialize the isc_tid_v.
+ *
+ * Requires:
+ *\li	'arg' is a valid isc_trampoline_t
+ *
+ * Returns:
+ *\li	return value from start_routine (see isc__trampoline_get())
+ */