summaryrefslogtreecommitdiffstats
path: root/lib/isc/rwlock.c
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--lib/isc/rwlock.c644
1 files changed, 644 insertions, 0 deletions
diff --git a/lib/isc/rwlock.c b/lib/isc/rwlock.c
new file mode 100644
index 0000000..156b469
--- /dev/null
+++ b/lib/isc/rwlock.c
@@ -0,0 +1,644 @@
+/*
+ * 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 <stdbool.h>
+#include <stddef.h>
+
+#if defined(sun) && (defined(__sparc) || defined(__sparc__))
+#include <synch.h> /* for smt_pause(3c) */
+#endif /* if defined(sun) && (defined(__sparc) || defined(__sparc__)) */
+
+#include <isc/atomic.h>
+#include <isc/magic.h>
+#include <isc/print.h>
+#include <isc/rwlock.h>
+#include <isc/util.h>
+
+#if USE_PTHREAD_RWLOCK
+
+#include <errno.h>
+#include <pthread.h>
+
+void
+isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
+ unsigned int write_quota) {
+ UNUSED(read_quota);
+ UNUSED(write_quota);
+ REQUIRE(pthread_rwlock_init(&rwl->rwlock, NULL) == 0);
+ atomic_init(&rwl->downgrade, false);
+}
+
+isc_result_t
+isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ switch (type) {
+ case isc_rwlocktype_read:
+ REQUIRE(pthread_rwlock_rdlock(&rwl->rwlock) == 0);
+ break;
+ case isc_rwlocktype_write:
+ while (true) {
+ REQUIRE(pthread_rwlock_wrlock(&rwl->rwlock) == 0);
+ /* Unlock if in middle of downgrade operation */
+ if (atomic_load_acquire(&rwl->downgrade)) {
+ REQUIRE(pthread_rwlock_unlock(&rwl->rwlock) ==
+ 0);
+ while (atomic_load_acquire(&rwl->downgrade)) {
+ }
+ continue;
+ }
+ break;
+ }
+ break;
+ default:
+ UNREACHABLE();
+ }
+ return (ISC_R_SUCCESS);
+}
+
+isc_result_t
+isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ int ret = 0;
+ switch (type) {
+ case isc_rwlocktype_read:
+ ret = pthread_rwlock_tryrdlock(&rwl->rwlock);
+ break;
+ case isc_rwlocktype_write:
+ ret = pthread_rwlock_trywrlock(&rwl->rwlock);
+ if ((ret == 0) && atomic_load_acquire(&rwl->downgrade)) {
+ isc_rwlock_unlock(rwl, type);
+ return (ISC_R_LOCKBUSY);
+ }
+ break;
+ default:
+ UNREACHABLE();
+ }
+
+ switch (ret) {
+ case 0:
+ return (ISC_R_SUCCESS);
+ case EBUSY:
+ return (ISC_R_LOCKBUSY);
+ case EAGAIN:
+ return (ISC_R_LOCKBUSY);
+ default:
+ UNREACHABLE();
+ }
+}
+
+isc_result_t
+isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ UNUSED(type);
+ REQUIRE(pthread_rwlock_unlock(&rwl->rwlock) == 0);
+ return (ISC_R_SUCCESS);
+}
+
+isc_result_t
+isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
+ UNUSED(rwl);
+ return (ISC_R_LOCKBUSY);
+}
+
+void
+isc_rwlock_downgrade(isc_rwlock_t *rwl) {
+ isc_result_t result;
+ atomic_store_release(&rwl->downgrade, true);
+ result = isc_rwlock_unlock(rwl, isc_rwlocktype_write);
+ RUNTIME_CHECK(result == ISC_R_SUCCESS);
+ result = isc_rwlock_lock(rwl, isc_rwlocktype_read);
+ RUNTIME_CHECK(result == ISC_R_SUCCESS);
+ atomic_store_release(&rwl->downgrade, false);
+}
+
+void
+isc_rwlock_destroy(isc_rwlock_t *rwl) {
+ pthread_rwlock_destroy(&rwl->rwlock);
+}
+
+#else /* if USE_PTHREAD_RWLOCK */
+
+#define RWLOCK_MAGIC ISC_MAGIC('R', 'W', 'L', 'k')
+#define VALID_RWLOCK(rwl) ISC_MAGIC_VALID(rwl, RWLOCK_MAGIC)
+
+#ifndef RWLOCK_DEFAULT_READ_QUOTA
+#define RWLOCK_DEFAULT_READ_QUOTA 4
+#endif /* ifndef RWLOCK_DEFAULT_READ_QUOTA */
+
+#ifndef RWLOCK_DEFAULT_WRITE_QUOTA
+#define RWLOCK_DEFAULT_WRITE_QUOTA 4
+#endif /* ifndef RWLOCK_DEFAULT_WRITE_QUOTA */
+
+#ifndef RWLOCK_MAX_ADAPTIVE_COUNT
+#define RWLOCK_MAX_ADAPTIVE_COUNT 100
+#endif /* ifndef RWLOCK_MAX_ADAPTIVE_COUNT */
+
+#if defined(_MSC_VER)
+#include <intrin.h>
+#define isc_rwlock_pause() YieldProcessor()
+#elif defined(__x86_64__)
+#include <immintrin.h>
+#define isc_rwlock_pause() _mm_pause()
+#elif defined(__i386__)
+#define isc_rwlock_pause() __asm__ __volatile__("rep; nop")
+#elif defined(__ia64__)
+#define isc_rwlock_pause() __asm__ __volatile__("hint @pause")
+#elif defined(__arm__) && HAVE_ARM_YIELD
+#define isc_rwlock_pause() __asm__ __volatile__("yield")
+#elif defined(sun) && (defined(__sparc) || defined(__sparc__))
+#define isc_rwlock_pause() smt_pause()
+#elif (defined(__sparc) || defined(__sparc__)) && HAVE_SPARC_PAUSE
+#define isc_rwlock_pause() __asm__ __volatile__("pause")
+#elif defined(__ppc__) || defined(_ARCH_PPC) || defined(_ARCH_PWR) || \
+ defined(_ARCH_PWR2) || defined(_POWER)
+#define isc_rwlock_pause() __asm__ volatile("or 27,27,27")
+#else /* if defined(_MSC_VER) */
+#define isc_rwlock_pause()
+#endif /* if defined(_MSC_VER) */
+
+static isc_result_t
+isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
+
+#ifdef ISC_RWLOCK_TRACE
+#include <stdio.h> /* Required for fprintf/stderr. */
+
+#include <isc/thread.h> /* Required for isc_thread_self(). */
+
+static void
+print_lock(const char *operation, isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ fprintf(stderr,
+ "rwlock %p thread %" PRIuPTR " %s(%s): "
+ "write_requests=%u, write_completions=%u, "
+ "cnt_and_flag=0x%x, readers_waiting=%u, "
+ "write_granted=%u, write_quota=%u\n",
+ rwl, isc_thread_self(), operation,
+ (type == isc_rwlocktype_read ? "read" : "write"),
+ atomic_load_acquire(&rwl->write_requests),
+ atomic_load_acquire(&rwl->write_completions),
+ atomic_load_acquire(&rwl->cnt_and_flag), rwl->readers_waiting,
+ atomic_load_acquire(&rwl->write_granted), rwl->write_quota);
+}
+#endif /* ISC_RWLOCK_TRACE */
+
+void
+isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
+ unsigned int write_quota) {
+ REQUIRE(rwl != NULL);
+
+ /*
+ * In case there's trouble initializing, we zero magic now. If all
+ * goes well, we'll set it to RWLOCK_MAGIC.
+ */
+ rwl->magic = 0;
+
+ atomic_init(&rwl->spins, 0);
+ atomic_init(&rwl->write_requests, 0);
+ atomic_init(&rwl->write_completions, 0);
+ atomic_init(&rwl->cnt_and_flag, 0);
+ rwl->readers_waiting = 0;
+ atomic_init(&rwl->write_granted, 0);
+ if (read_quota != 0) {
+ UNEXPECTED_ERROR("read quota is not supported");
+ }
+ if (write_quota == 0) {
+ write_quota = RWLOCK_DEFAULT_WRITE_QUOTA;
+ }
+ rwl->write_quota = write_quota;
+
+ isc_mutex_init(&rwl->lock);
+
+ isc_condition_init(&rwl->readable);
+ isc_condition_init(&rwl->writeable);
+
+ rwl->magic = RWLOCK_MAGIC;
+}
+
+void
+isc_rwlock_destroy(isc_rwlock_t *rwl) {
+ REQUIRE(VALID_RWLOCK(rwl));
+
+ REQUIRE(atomic_load_acquire(&rwl->write_requests) ==
+ atomic_load_acquire(&rwl->write_completions) &&
+ atomic_load_acquire(&rwl->cnt_and_flag) == 0 &&
+ rwl->readers_waiting == 0);
+
+ rwl->magic = 0;
+ (void)isc_condition_destroy(&rwl->readable);
+ (void)isc_condition_destroy(&rwl->writeable);
+ isc_mutex_destroy(&rwl->lock);
+}
+
+/*
+ * When some architecture-dependent atomic operations are available,
+ * rwlock can be more efficient than the generic algorithm defined below.
+ * The basic algorithm is described in the following URL:
+ * http://www.cs.rochester.edu/u/scott/synchronization/pseudocode/rw.html
+ *
+ * The key is to use the following integer variables modified atomically:
+ * write_requests, write_completions, and cnt_and_flag.
+ *
+ * write_requests and write_completions act as a waiting queue for writers
+ * in order to ensure the FIFO order. Both variables begin with the initial
+ * value of 0. When a new writer tries to get a write lock, it increments
+ * write_requests and gets the previous value of the variable as a "ticket".
+ * When write_completions reaches the ticket number, the new writer can start
+ * writing. When the writer completes its work, it increments
+ * write_completions so that another new writer can start working. If the
+ * write_requests is not equal to write_completions, it means a writer is now
+ * working or waiting. In this case, a new readers cannot start reading, or
+ * in other words, this algorithm basically prefers writers.
+ *
+ * cnt_and_flag is a "lock" shared by all readers and writers. This integer
+ * variable is a kind of structure with two members: writer_flag (1 bit) and
+ * reader_count (31 bits). The writer_flag shows whether a writer is working,
+ * and the reader_count shows the number of readers currently working or almost
+ * ready for working. A writer who has the current "ticket" tries to get the
+ * lock by exclusively setting the writer_flag to 1, provided that the whole
+ * 32-bit is 0 (meaning no readers or writers working). On the other hand,
+ * a new reader tries to increment the "reader_count" field provided that
+ * the writer_flag is 0 (meaning there is no writer working).
+ *
+ * If some of the above operations fail, the reader or the writer sleeps
+ * until the related condition changes. When a working reader or writer
+ * completes its work, some readers or writers are sleeping, and the condition
+ * that suspended the reader or writer has changed, it wakes up the sleeping
+ * readers or writers.
+ *
+ * As already noted, this algorithm basically prefers writers. In order to
+ * prevent readers from starving, however, the algorithm also introduces the
+ * "writer quota" (Q). When Q consecutive writers have completed their work,
+ * suspending readers, the last writer will wake up the readers, even if a new
+ * writer is waiting.
+ *
+ * Implementation specific note: due to the combination of atomic operations
+ * and a mutex lock, ordering between the atomic operation and locks can be
+ * very sensitive in some cases. In particular, it is generally very important
+ * to check the atomic variable that requires a reader or writer to sleep after
+ * locking the mutex and before actually sleeping; otherwise, it could be very
+ * likely to cause a deadlock. For example, assume "var" is a variable
+ * atomically modified, then the corresponding code would be:
+ * if (var == need_sleep) {
+ * LOCK(lock);
+ * if (var == need_sleep)
+ * WAIT(cond, lock);
+ * UNLOCK(lock);
+ * }
+ * The second check is important, since "var" is protected by the atomic
+ * operation, not by the mutex, and can be changed just before sleeping.
+ * (The first "if" could be omitted, but this is also important in order to
+ * make the code efficient by avoiding the use of the mutex unless it is
+ * really necessary.)
+ */
+
+#define WRITER_ACTIVE 0x1
+#define READER_INCR 0x2
+
+static isc_result_t
+isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ int32_t cntflag;
+
+ REQUIRE(VALID_RWLOCK(rwl));
+
+#ifdef ISC_RWLOCK_TRACE
+ print_lock("prelock", rwl, type);
+#endif /* ifdef ISC_RWLOCK_TRACE */
+
+ if (type == isc_rwlocktype_read) {
+ if (atomic_load_acquire(&rwl->write_requests) !=
+ atomic_load_acquire(&rwl->write_completions))
+ {
+ /* there is a waiting or active writer */
+ LOCK(&rwl->lock);
+ if (atomic_load_acquire(&rwl->write_requests) !=
+ atomic_load_acquire(&rwl->write_completions))
+ {
+ rwl->readers_waiting++;
+ WAIT(&rwl->readable, &rwl->lock);
+ rwl->readers_waiting--;
+ }
+ UNLOCK(&rwl->lock);
+ }
+
+ cntflag = atomic_fetch_add_release(&rwl->cnt_and_flag,
+ READER_INCR);
+ POST(cntflag);
+ while (1) {
+ if ((atomic_load_acquire(&rwl->cnt_and_flag) &
+ WRITER_ACTIVE) == 0)
+ {
+ break;
+ }
+
+ /* A writer is still working */
+ LOCK(&rwl->lock);
+ rwl->readers_waiting++;
+ if ((atomic_load_acquire(&rwl->cnt_and_flag) &
+ WRITER_ACTIVE) != 0)
+ {
+ WAIT(&rwl->readable, &rwl->lock);
+ }
+ rwl->readers_waiting--;
+ UNLOCK(&rwl->lock);
+
+ /*
+ * Typically, the reader should be able to get a lock
+ * at this stage:
+ * (1) there should have been no pending writer when
+ * the reader was trying to increment the
+ * counter; otherwise, the writer should be in
+ * the waiting queue, preventing the reader from
+ * proceeding to this point.
+ * (2) once the reader increments the counter, no
+ * more writer can get a lock.
+ * Still, it is possible another writer can work at
+ * this point, e.g. in the following scenario:
+ * A previous writer unlocks the writer lock.
+ * This reader proceeds to point (1).
+ * A new writer appears, and gets a new lock before
+ * the reader increments the counter.
+ * The reader then increments the counter.
+ * The previous writer notices there is a waiting
+ * reader who is almost ready, and wakes it up.
+ * So, the reader needs to confirm whether it can now
+ * read explicitly (thus we loop). Note that this is
+ * not an infinite process, since the reader has
+ * incremented the counter at this point.
+ */
+ }
+
+ /*
+ * If we are temporarily preferred to writers due to the writer
+ * quota, reset the condition (race among readers doesn't
+ * matter).
+ */
+ atomic_store_release(&rwl->write_granted, 0);
+ } else {
+ int32_t prev_writer;
+
+ /* enter the waiting queue, and wait for our turn */
+ prev_writer = atomic_fetch_add_release(&rwl->write_requests, 1);
+ while (atomic_load_acquire(&rwl->write_completions) !=
+ prev_writer)
+ {
+ LOCK(&rwl->lock);
+ if (atomic_load_acquire(&rwl->write_completions) !=
+ prev_writer)
+ {
+ WAIT(&rwl->writeable, &rwl->lock);
+ UNLOCK(&rwl->lock);
+ continue;
+ }
+ UNLOCK(&rwl->lock);
+ break;
+ }
+
+ while (!atomic_compare_exchange_weak_acq_rel(
+ &rwl->cnt_and_flag, &(int_fast32_t){ 0 },
+ WRITER_ACTIVE))
+ {
+ /* Another active reader or writer is working. */
+ LOCK(&rwl->lock);
+ if (atomic_load_acquire(&rwl->cnt_and_flag) != 0) {
+ WAIT(&rwl->writeable, &rwl->lock);
+ }
+ UNLOCK(&rwl->lock);
+ }
+
+ INSIST((atomic_load_acquire(&rwl->cnt_and_flag) &
+ WRITER_ACTIVE));
+ atomic_fetch_add_release(&rwl->write_granted, 1);
+ }
+
+#ifdef ISC_RWLOCK_TRACE
+ print_lock("postlock", rwl, type);
+#endif /* ifdef ISC_RWLOCK_TRACE */
+
+ return (ISC_R_SUCCESS);
+}
+
+isc_result_t
+isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ int32_t cnt = 0;
+ int32_t spins = atomic_load_acquire(&rwl->spins) * 2 + 10;
+ int32_t max_cnt = ISC_MAX(spins, RWLOCK_MAX_ADAPTIVE_COUNT);
+ isc_result_t result = ISC_R_SUCCESS;
+
+ do {
+ if (cnt++ >= max_cnt) {
+ result = isc__rwlock_lock(rwl, type);
+ break;
+ }
+ isc_rwlock_pause();
+ } while (isc_rwlock_trylock(rwl, type) != ISC_R_SUCCESS);
+
+ atomic_fetch_add_release(&rwl->spins, (cnt - spins) / 8);
+
+ return (result);
+}
+
+isc_result_t
+isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ int32_t cntflag;
+
+ REQUIRE(VALID_RWLOCK(rwl));
+
+#ifdef ISC_RWLOCK_TRACE
+ print_lock("prelock", rwl, type);
+#endif /* ifdef ISC_RWLOCK_TRACE */
+
+ if (type == isc_rwlocktype_read) {
+ /* If a writer is waiting or working, we fail. */
+ if (atomic_load_acquire(&rwl->write_requests) !=
+ atomic_load_acquire(&rwl->write_completions))
+ {
+ return (ISC_R_LOCKBUSY);
+ }
+
+ /* Otherwise, be ready for reading. */
+ cntflag = atomic_fetch_add_release(&rwl->cnt_and_flag,
+ READER_INCR);
+ if ((cntflag & WRITER_ACTIVE) != 0) {
+ /*
+ * A writer is working. We lose, and cancel the read
+ * request.
+ */
+ cntflag = atomic_fetch_sub_release(&rwl->cnt_and_flag,
+ READER_INCR);
+ /*
+ * If no other readers are waiting and we've suspended
+ * new writers in this short period, wake them up.
+ */
+ if (cntflag == READER_INCR &&
+ atomic_load_acquire(&rwl->write_completions) !=
+ atomic_load_acquire(&rwl->write_requests))
+ {
+ LOCK(&rwl->lock);
+ BROADCAST(&rwl->writeable);
+ UNLOCK(&rwl->lock);
+ }
+
+ return (ISC_R_LOCKBUSY);
+ }
+ } else {
+ /* Try locking without entering the waiting queue. */
+ int_fast32_t zero = 0;
+ if (!atomic_compare_exchange_strong_acq_rel(
+ &rwl->cnt_and_flag, &zero, WRITER_ACTIVE))
+ {
+ return (ISC_R_LOCKBUSY);
+ }
+
+ /*
+ * XXXJT: jump into the queue, possibly breaking the writer
+ * order.
+ */
+ atomic_fetch_sub_release(&rwl->write_completions, 1);
+ atomic_fetch_add_release(&rwl->write_granted, 1);
+ }
+
+#ifdef ISC_RWLOCK_TRACE
+ print_lock("postlock", rwl, type);
+#endif /* ifdef ISC_RWLOCK_TRACE */
+
+ return (ISC_R_SUCCESS);
+}
+
+isc_result_t
+isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
+ REQUIRE(VALID_RWLOCK(rwl));
+
+ int_fast32_t reader_incr = READER_INCR;
+
+ /* Try to acquire write access. */
+ atomic_compare_exchange_strong_acq_rel(&rwl->cnt_and_flag, &reader_incr,
+ WRITER_ACTIVE);
+ /*
+ * There must have been no writer, and there must have
+ * been at least one reader.
+ */
+ INSIST((reader_incr & WRITER_ACTIVE) == 0 &&
+ (reader_incr & ~WRITER_ACTIVE) != 0);
+
+ if (reader_incr == READER_INCR) {
+ /*
+ * We are the only reader and have been upgraded.
+ * Now jump into the head of the writer waiting queue.
+ */
+ atomic_fetch_sub_release(&rwl->write_completions, 1);
+ } else {
+ return (ISC_R_LOCKBUSY);
+ }
+
+ return (ISC_R_SUCCESS);
+}
+
+void
+isc_rwlock_downgrade(isc_rwlock_t *rwl) {
+ int32_t prev_readers;
+
+ REQUIRE(VALID_RWLOCK(rwl));
+
+ /* Become an active reader. */
+ prev_readers = atomic_fetch_add_release(&rwl->cnt_and_flag,
+ READER_INCR);
+ /* We must have been a writer. */
+ INSIST((prev_readers & WRITER_ACTIVE) != 0);
+
+ /* Complete write */
+ atomic_fetch_sub_release(&rwl->cnt_and_flag, WRITER_ACTIVE);
+ atomic_fetch_add_release(&rwl->write_completions, 1);
+
+ /* Resume other readers */
+ LOCK(&rwl->lock);
+ if (rwl->readers_waiting > 0) {
+ BROADCAST(&rwl->readable);
+ }
+ UNLOCK(&rwl->lock);
+}
+
+isc_result_t
+isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
+ int32_t prev_cnt;
+
+ REQUIRE(VALID_RWLOCK(rwl));
+
+#ifdef ISC_RWLOCK_TRACE
+ print_lock("preunlock", rwl, type);
+#endif /* ifdef ISC_RWLOCK_TRACE */
+
+ if (type == isc_rwlocktype_read) {
+ prev_cnt = atomic_fetch_sub_release(&rwl->cnt_and_flag,
+ READER_INCR);
+ /*
+ * If we're the last reader and any writers are waiting, wake
+ * them up. We need to wake up all of them to ensure the
+ * FIFO order.
+ */
+ if (prev_cnt == READER_INCR &&
+ atomic_load_acquire(&rwl->write_completions) !=
+ atomic_load_acquire(&rwl->write_requests))
+ {
+ LOCK(&rwl->lock);
+ BROADCAST(&rwl->writeable);
+ UNLOCK(&rwl->lock);
+ }
+ } else {
+ bool wakeup_writers = true;
+
+ /*
+ * Reset the flag, and (implicitly) tell other writers
+ * we are done.
+ */
+ atomic_fetch_sub_release(&rwl->cnt_and_flag, WRITER_ACTIVE);
+ atomic_fetch_add_release(&rwl->write_completions, 1);
+
+ if ((atomic_load_acquire(&rwl->write_granted) >=
+ rwl->write_quota) ||
+ (atomic_load_acquire(&rwl->write_requests) ==
+ atomic_load_acquire(&rwl->write_completions)) ||
+ (atomic_load_acquire(&rwl->cnt_and_flag) & ~WRITER_ACTIVE))
+ {
+ /*
+ * We have passed the write quota, no writer is
+ * waiting, or some readers are almost ready, pending
+ * possible writers. Note that the last case can
+ * happen even if write_requests != write_completions
+ * (which means a new writer in the queue), so we need
+ * to catch the case explicitly.
+ */
+ LOCK(&rwl->lock);
+ if (rwl->readers_waiting > 0) {
+ wakeup_writers = false;
+ BROADCAST(&rwl->readable);
+ }
+ UNLOCK(&rwl->lock);
+ }
+
+ if ((atomic_load_acquire(&rwl->write_requests) !=
+ atomic_load_acquire(&rwl->write_completions)) &&
+ wakeup_writers)
+ {
+ LOCK(&rwl->lock);
+ BROADCAST(&rwl->writeable);
+ UNLOCK(&rwl->lock);
+ }
+ }
+
+#ifdef ISC_RWLOCK_TRACE
+ print_lock("postunlock", rwl, type);
+#endif /* ifdef ISC_RWLOCK_TRACE */
+
+ return (ISC_R_SUCCESS);
+}
+
+#endif /* USE_PTHREAD_RWLOCK */
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-09 15:50:56 +0000