/* $NetBSD: trampoline.c,v 1.2.2.1 2024/02/25 15:47:19 martin Exp $ */ /* * 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. */ /*! \file */ #include #include #include #include #include #include #include #include "mem_p.h" #include "trampoline_p.h" #define ISC__TRAMPOLINE_UNUSED 0 struct isc__trampoline { int tid; /* const */ uintptr_t self; isc_threadfunc_t start; isc_threadarg_t arg; void *jemalloc_enforce_init; }; /* * We can't use isc_mem API here, because it's called too early and the * isc_mem_debugging flags can be changed later causing mismatch between flags * used for isc_mem_get() and isc_mem_put(). * * Since this is a single allocation at library load and deallocation at library * unload, using the standard allocator without the tracking is fine for this * single purpose. * * We can't use isc_mutex API either, because we track whether the mutexes get * properly destroyed, and we intentionally leak the static mutex here without * destroying it to prevent data race between library destructor running while * thread is being still created. */ static uv_mutex_t isc__trampoline_lock; static isc__trampoline_t **trampolines; thread_local size_t isc_tid_v = SIZE_MAX; static size_t isc__trampoline_min = 1; static size_t isc__trampoline_max = 65; static isc__trampoline_t * isc__trampoline_new(int tid, isc_threadfunc_t start, isc_threadarg_t arg) { isc__trampoline_t *trampoline = calloc(1, sizeof(*trampoline)); RUNTIME_CHECK(trampoline != NULL); *trampoline = (isc__trampoline_t){ .tid = tid, .start = start, .arg = arg, .self = ISC__TRAMPOLINE_UNUSED, }; return (trampoline); } void isc__trampoline_initialize(void) { uv_mutex_init(&isc__trampoline_lock); trampolines = calloc(isc__trampoline_max, sizeof(trampolines[0])); RUNTIME_CHECK(trampolines != NULL); /* Get the trampoline slot 0 for the main thread */ trampolines[0] = isc__trampoline_new(0, NULL, NULL); isc_tid_v = trampolines[0]->tid; trampolines[0]->self = isc_thread_self(); /* Initialize the other trampolines */ for (size_t i = 1; i < isc__trampoline_max; i++) { trampolines[i] = NULL; } isc__trampoline_min = 1; } void isc__trampoline_shutdown(void) { /* * When the program using the library exits abruptly and the library * gets unloaded, there might be some existing trampolines from unjoined * threads. We intentionally ignore those and don't check whether all * trampolines have been cleared before exiting, so we leak a little bit * of resources here, including the lock. */ free(trampolines[0]); } isc__trampoline_t * isc__trampoline_get(isc_threadfunc_t start, isc_threadarg_t arg) { isc__trampoline_t **tmp = NULL; isc__trampoline_t *trampoline = NULL; uv_mutex_lock(&isc__trampoline_lock); again: for (size_t i = isc__trampoline_min; i < isc__trampoline_max; i++) { if (trampolines[i] == NULL) { trampoline = isc__trampoline_new(i, start, arg); trampolines[i] = trampoline; isc__trampoline_min = i + 1; goto done; } } tmp = calloc(2 * isc__trampoline_max, sizeof(trampolines[0])); RUNTIME_CHECK(tmp != NULL); for (size_t i = 0; i < isc__trampoline_max; i++) { tmp[i] = trampolines[i]; } for (size_t i = isc__trampoline_max; i < 2 * isc__trampoline_max; i++) { tmp[i] = NULL; } free(trampolines); trampolines = tmp; isc__trampoline_max = isc__trampoline_max * 2; goto again; done: INSIST(trampoline != NULL); uv_mutex_unlock(&isc__trampoline_lock); return (trampoline); } void isc__trampoline_detach(isc__trampoline_t *trampoline) { uv_mutex_lock(&isc__trampoline_lock); REQUIRE(trampoline->self == isc_thread_self()); REQUIRE(trampoline->tid > 0); REQUIRE((size_t)trampoline->tid < isc__trampoline_max); REQUIRE(trampolines[trampoline->tid] == trampoline); trampolines[trampoline->tid] = NULL; if (isc__trampoline_min > (size_t)trampoline->tid) { isc__trampoline_min = trampoline->tid; } isc__mem_free_noctx(trampoline->jemalloc_enforce_init, 8); free(trampoline); uv_mutex_unlock(&isc__trampoline_lock); return; } void isc__trampoline_attach(isc__trampoline_t *trampoline) { uv_mutex_lock(&isc__trampoline_lock); REQUIRE(trampoline->self == ISC__TRAMPOLINE_UNUSED); REQUIRE(trampoline->tid > 0); REQUIRE((size_t)trampoline->tid < isc__trampoline_max); REQUIRE(trampolines[trampoline->tid] == trampoline); /* Initialize the trampoline */ isc_tid_v = trampoline->tid; trampoline->self = isc_thread_self(); /* * Ensure every thread starts with a malloc() call to prevent memory * bloat caused by a jemalloc quirk. While this dummy allocation is * not used for anything, free() must not be immediately called for it * so that an optimizing compiler does not strip away such a pair of * malloc() + free() calls altogether, as it would foil the fix. */ trampoline->jemalloc_enforce_init = isc__mem_alloc_noctx(8); uv_mutex_unlock(&isc__trampoline_lock); } isc_threadresult_t isc__trampoline_run(isc_threadarg_t arg) { isc__trampoline_t *trampoline = (isc__trampoline_t *)arg; isc_threadresult_t result; isc__trampoline_attach(trampoline); /* Run the main function */ result = (trampoline->start)(trampoline->arg); isc__trampoline_detach(trampoline); return (result); }