1 files changed, 194 insertions, 0 deletions
diff --git a/lib/isc/trampoline.c b/lib/isc/trampoline.c
new file mode 100644
index 0000000..58171d9
--- /dev/null
+++ b/lib/isc/trampoline.c
@@ -0,0 +1,194 @@
+/*
+ * 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 <inttypes.h>
+#include <stdlib.h>
+#include <uv.h>
+
+#include <isc/mem.h>
+#include <isc/once.h>
+#include <isc/thread.h>
+#include <isc/util.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;
+	}
+
+	free(trampoline->jemalloc_enforce_init);
+	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 = malloc(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);
+}