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247 lines
7.5 KiB
C++
247 lines
7.5 KiB
C++
/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
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// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
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#ident "$Id: frwlock.h 45930 2012-07-19 19:18:35Z zardosht $"
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#ident "Copyright (c) 2007-2012 Tokutek Inc. All rights reserved."
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#ident "The technology is licensed by the Massachusetts Institute of Technology, Rutgers State University of New Jersey, and the Research Foundation of State University of New York at Stony Brook under United States of America Serial No. 11/760379 and to the patents and/or patent applications resulting from it."
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#include <toku_assert.h>
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namespace toku {
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void frwlock::init(toku_mutex_t *const mutex) {
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m_mutex = mutex;
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m_num_readers = 0;
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m_num_writers = 0;
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m_num_want_write = 0;
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m_num_want_read = 0;
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m_num_signaled_readers = 0;
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m_num_expensive_want_write = 0;
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toku_cond_init(&m_wait_read, nullptr);
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m_queue_item_read.cond = &m_wait_read;
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m_queue_item_read.next = nullptr;
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m_wait_read_is_in_queue = false;
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m_current_writer_expensive = false;
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m_read_wait_expensive = false;
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m_wait_head = nullptr;
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m_wait_tail = nullptr;
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}
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void frwlock::deinit(void) {
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toku_cond_destroy(&m_wait_read);
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}
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inline bool frwlock::queue_is_empty(void) const {
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return m_wait_head == nullptr;
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}
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inline void frwlock::enq_item(queue_item *const item) {
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paranoid_invariant_null(item->next);
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if (m_wait_tail != nullptr) {
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m_wait_tail->next = item;
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} else {
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paranoid_invariant_null(m_wait_head);
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m_wait_head = item;
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}
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m_wait_tail = item;
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}
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inline toku_cond_t *frwlock::deq_item(void) {
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paranoid_invariant_notnull(m_wait_head);
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paranoid_invariant_notnull(m_wait_tail);
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queue_item *item = m_wait_head;
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m_wait_head = m_wait_head->next;
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if (m_wait_tail == item) {
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m_wait_tail = nullptr;
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}
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return item->cond;
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}
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// Prerequisite: Holds m_mutex.
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inline void frwlock::write_lock(bool expensive) {
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toku_mutex_assert_locked(m_mutex);
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if (this->try_write_lock(expensive)) {
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return;
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}
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toku_cond_t cond = TOKU_COND_INITIALIZER;
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queue_item item = { .cond = &cond, .next = nullptr };
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this->enq_item(&item);
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// Wait for our turn.
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++m_num_want_write;
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if (expensive) {
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++m_num_expensive_want_write;
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}
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toku_cond_wait(&cond, m_mutex);
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toku_cond_destroy(&cond);
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// Now it's our turn.
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paranoid_invariant(m_num_want_write > 0);
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paranoid_invariant_zero(m_num_readers);
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paranoid_invariant_zero(m_num_writers);
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paranoid_invariant_zero(m_num_signaled_readers);
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// Not waiting anymore; grab the lock.
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--m_num_want_write;
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if (expensive) {
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--m_num_expensive_want_write;
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}
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m_num_writers = 1;
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m_current_writer_expensive = expensive;
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}
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inline bool frwlock::try_write_lock(bool expensive) {
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toku_mutex_assert_locked(m_mutex);
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if (m_num_readers > 0 || m_num_writers > 0 || m_num_signaled_readers > 0 || m_num_want_write > 0) {
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return false;
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}
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// No one holds the lock. Grant the write lock.
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paranoid_invariant_zero(m_num_want_write);
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paranoid_invariant_zero(m_num_want_read);
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m_num_writers = 1;
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m_current_writer_expensive = expensive;
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return true;
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}
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inline void frwlock::read_lock(void) {
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toku_mutex_assert_locked(m_mutex);
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if (m_num_writers > 0 || m_num_want_write > 0) {
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if (!m_wait_read_is_in_queue) {
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// Throw the read cond_t onto the queue.
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paranoid_invariant(m_num_signaled_readers == m_num_want_read);
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m_queue_item_read.next = nullptr;
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this->enq_item(&m_queue_item_read);
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m_wait_read_is_in_queue = true;
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paranoid_invariant(!m_read_wait_expensive);
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m_read_wait_expensive = (
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m_current_writer_expensive ||
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(m_num_expensive_want_write > 0)
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);
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}
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// Wait for our turn.
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++m_num_want_read;
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toku_cond_wait(&m_wait_read, m_mutex);
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// Now it's our turn.
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paranoid_invariant_zero(m_num_writers);
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paranoid_invariant(m_num_want_read > 0);
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paranoid_invariant(m_num_signaled_readers > 0);
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// Not waiting anymore; grab the lock.
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--m_num_want_read;
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--m_num_signaled_readers;
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}
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++m_num_readers;
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}
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inline bool frwlock::try_read_lock(void) {
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toku_mutex_assert_locked(m_mutex);
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if (m_num_writers > 0 || m_num_want_write > 0) {
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return false;
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}
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// No writer holds the lock.
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// No writers are waiting.
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// Grant the read lock.
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++m_num_readers;
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return true;
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}
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inline void frwlock::maybe_signal_next_writer(void) {
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if (m_num_want_write > 0 && m_num_signaled_readers == 0 && m_num_readers == 0) {
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toku_cond_t *cond = this->deq_item();
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paranoid_invariant(cond != &m_wait_read);
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// Grant write lock to waiting writer.
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paranoid_invariant(m_num_want_write > 0);
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toku_cond_signal(cond);
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}
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}
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inline void frwlock::read_unlock(void) {
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toku_mutex_assert_locked(m_mutex);
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paranoid_invariant(m_num_writers == 0);
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paranoid_invariant(m_num_readers > 0);
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--m_num_readers;
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this->maybe_signal_next_writer();
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}
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inline bool frwlock::read_lock_is_expensive(void) {
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toku_mutex_assert_locked(m_mutex);
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if (m_wait_read_is_in_queue) {
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return m_read_wait_expensive;
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}
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else {
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return m_current_writer_expensive || (m_num_expensive_want_write > 0);
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}
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}
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inline void frwlock::maybe_signal_or_broadcast_next(void) {
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paranoid_invariant(m_num_signaled_readers == 0);
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if (this->queue_is_empty()) {
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paranoid_invariant(m_num_want_write == 0);
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paranoid_invariant(m_num_want_read == 0);
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return;
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}
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toku_cond_t *cond = this->deq_item();
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if (cond == &m_wait_read) {
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// Grant read locks to all waiting readers
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paranoid_invariant(m_wait_read_is_in_queue);
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paranoid_invariant(m_num_want_read > 0);
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m_num_signaled_readers = m_num_want_read;
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m_wait_read_is_in_queue = false;
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m_read_wait_expensive = false;
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toku_cond_broadcast(cond);
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}
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else {
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// Grant write lock to waiting writer.
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paranoid_invariant(m_num_want_write > 0);
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toku_cond_signal(cond);
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}
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}
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inline void frwlock::write_unlock(void) {
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toku_mutex_assert_locked(m_mutex);
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paranoid_invariant(m_num_writers == 1);
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m_num_writers = 0;
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m_current_writer_expensive = false;
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this->maybe_signal_or_broadcast_next();
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}
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inline bool frwlock::write_lock_is_expensive(void) {
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toku_mutex_assert_locked(m_mutex);
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return (m_num_expensive_want_write > 0) || (m_current_writer_expensive);
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}
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inline uint32_t frwlock::users(void) const {
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toku_mutex_assert_locked(m_mutex);
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return m_num_readers + m_num_writers + m_num_want_read + m_num_want_write;
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}
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inline uint32_t frwlock::blocked_users(void) const {
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toku_mutex_assert_locked(m_mutex);
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return m_num_want_read + m_num_want_write;
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}
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inline uint32_t frwlock::writers(void) const {
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// this is sometimes called as "assert(lock->writers())" when we
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// assume we have the write lock. if that's the assumption, we may
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// not own the mutex, so we don't assert_locked here
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return m_num_writers;
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}
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inline uint32_t frwlock::blocked_writers(void) const {
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toku_mutex_assert_locked(m_mutex);
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return m_num_want_write;
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}
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inline uint32_t frwlock::readers(void) const {
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toku_mutex_assert_locked(m_mutex);
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return m_num_readers;
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}
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inline uint32_t frwlock::blocked_readers(void) const {
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toku_mutex_assert_locked(m_mutex);
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return m_num_want_read;
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}
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} // namespace toku
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