mariadb/locktree/lock_request.cc

/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
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  TokuDB, Tokutek Fractal Tree Indexing Library.
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#ident "Copyright (c) 2007-2013 Tokutek Inc.  All rights reserved."
#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."

#include <toku_race_tools.h>

#include <ft/ybt.h>

#include "locktree.h"
#include "lock_request.h"

namespace toku {

// initialize a lock request's internals
void lock_request::create(uint64_t wait_time) {
    m_txnid = TXNID_NONE;
    m_left_key = nullptr;
    m_right_key = nullptr;
    toku_init_dbt(&m_left_key_copy);
    toku_init_dbt(&m_right_key_copy);

    m_type = type::UNKNOWN;
    m_lt = nullptr;

    m_complete_r = 0;
    m_state = state::UNINITIALIZED;

    m_wait_time = wait_time;
    toku_cond_init(&m_wait_cond, nullptr);
}

// destroy a lock request.
void lock_request::destroy(void) {
    toku_destroy_dbt(&m_left_key_copy);
    toku_destroy_dbt(&m_right_key_copy);
    toku_cond_destroy(&m_wait_cond);
}

// set the lock request parameters. this API allows a lock request to be reused.
void lock_request::set(locktree *lt, TXNID txnid,
        const DBT *left_key, const DBT *right_key,
        lock_request::type lock_type) {
    invariant(m_state != state::PENDING);
    m_lt = lt;
    m_txnid = txnid;
    m_left_key = left_key;
    m_right_key = right_key;
    toku_destroy_dbt(&m_left_key_copy);
    toku_destroy_dbt(&m_right_key_copy);
    m_type = lock_type;
    m_state = state::INITIALIZED;
    m_info = lt->get_lock_request_info();
}

// get rid of any stored left and right key copies and
// replace them with copies of the given left and right key
void lock_request::copy_keys() {
    if (!toku_dbt_is_infinite(m_left_key)) {
        toku_clone_dbt(&m_left_key_copy, *m_left_key);
        m_left_key = &m_left_key_copy;
    }
    if (!toku_dbt_is_infinite(m_right_key)) {
        toku_clone_dbt(&m_right_key_copy, *m_right_key);
        m_right_key = &m_right_key_copy;
    }
}

// what are the conflicts for this pending lock request?
void lock_request::get_conflicts(txnid_set *conflicts) {
    invariant(m_state == state::PENDING);
    const bool is_write_request = m_type == type::WRITE;
    m_lt->get_conflicts(is_write_request, m_txnid, m_left_key, m_right_key, conflicts);
}

// build a wait-for-graph for this lock request and the given conflict set
// for each transaction B that blocks A's lock request
//     if B is blocked then
//         add (A,T) to the WFG and if B is new, fill in the WFG from B
void lock_request::build_wait_graph(wfg *wait_graph, const txnid_set &conflicts) {
    size_t num_conflicts = conflicts.size();
    for (size_t i = 0; i < num_conflicts; i++) {
        TXNID conflicting_txnid = conflicts.get(i);
        lock_request *conflicting_request = find_lock_request(conflicting_txnid);
        invariant(conflicting_txnid != m_txnid);
        invariant(conflicting_request != this);
        if (conflicting_request) {
            bool already_exists = wait_graph->node_exists(conflicting_txnid);
            wait_graph->add_edge(m_txnid, conflicting_txnid);
            if (!already_exists) {
                // recursively build the wait for graph rooted at the conflicting
                // request, given its set of lock conflicts.
                txnid_set other_conflicts;
                other_conflicts.create();
                conflicting_request->get_conflicts(&other_conflicts);
                conflicting_request->build_wait_graph(wait_graph, other_conflicts);
                other_conflicts.destroy();
            }
        }
    }
}

// returns: true if the current set of lock requests contains
//          a deadlock, false otherwise.
bool lock_request::deadlock_exists(const txnid_set &conflicts) {
    wfg wait_graph;
    wait_graph.create();

    build_wait_graph(&wait_graph, conflicts);
    bool deadlock = wait_graph.cycle_exists_from_txnid(m_txnid);

    wait_graph.destroy();
    return deadlock;
}

// try to acquire a lock described by this lock request. 
int lock_request::start(void) {
    int r;

    txnid_set conflicts;
    conflicts.create();
    if (m_type == type::WRITE) {
        r = m_lt->acquire_write_lock(m_txnid, m_left_key, m_right_key, &conflicts);
    } else {
        invariant(m_type == type::READ);
        r = m_lt->acquire_read_lock(m_txnid, m_left_key, m_right_key, &conflicts);
    }

    // if the lock is not granted, save it to the set of lock requests
    // and check for a deadlock. if there is one, complete it as failed
    if (r == DB_LOCK_NOTGRANTED) {
        copy_keys();
        toku_mutex_lock(&m_info->mutex);
        m_state = state::PENDING;
        insert_into_lock_requests();
        if (deadlock_exists(conflicts)) {
            remove_from_lock_requests();
            complete(DB_LOCK_DEADLOCK);
        }
        toku_mutex_unlock(&m_info->mutex);
    } else {
        complete(r);
    }

    conflicts.destroy();
    return m_state == state::COMPLETE ? m_complete_r : r;
}

void lock_request::calculate_cond_wakeup_time(struct timespec *ts) {
    struct timeval now;
    int r = gettimeofday(&now, NULL);
    invariant_zero(r);
    int64_t sec = now.tv_sec + (m_wait_time / 1000);
    int64_t usec = now.tv_usec + ((m_wait_time % 1000) * 1000);
    int64_t d_sec = usec / 1000000;
    int64_t d_usec = usec % 1000000;
    ts->tv_sec = sec + d_sec;
    ts->tv_nsec = d_usec * 1000;
}

// sleep on the lock request until it becomes resolved or the wait time has elapsed.
int lock_request::wait(void) {
    toku_mutex_lock(&m_info->mutex);
    while (m_state == state::PENDING) {
        struct timespec ts;
        calculate_cond_wakeup_time(&ts);
        int r = toku_cond_timedwait(&m_wait_cond, &m_info->mutex, &ts);
        invariant(r == 0 || r == ETIMEDOUT);
        if (r == ETIMEDOUT && m_state == state::PENDING) {
            // if we're still pending and we timed out, then remove our
            // request from the set of lock requests and fail.
            remove_from_lock_requests();
            // complete sets m_state to COMPLETE, breaking us out of the loop
            complete(DB_LOCK_NOTGRANTED);
        }
    }
    toku_mutex_unlock(&m_info->mutex);

    invariant(m_state == state::COMPLETE);
    return m_complete_r;
}

// complete this lock request with the given return value
void lock_request::complete(int complete_r) {
    m_state = state::COMPLETE;
    m_complete_r = complete_r;
}

const DBT *lock_request::get_left_key(void) const {
    return m_left_key;
}

const DBT *lock_request::get_right_key(void) const {
    return m_right_key;
}

int lock_request::retry(void) {
    int r;

    invariant(m_state == state::PENDING);
    if (m_type == type::WRITE) {
        r = m_lt->acquire_write_lock(m_txnid, m_left_key, m_right_key, nullptr);
    } else {
        r = m_lt->acquire_read_lock(m_txnid, m_left_key, m_right_key, nullptr);
    }

    // if the acquisition succeeded then remove ourselves from the
    // set of lock requests, complete, and signal the waiting thread.
    if (r == 0) {
        remove_from_lock_requests();
        complete(r);
        toku_cond_broadcast(&m_wait_cond);
    }

    return r;
}

void lock_request::retry_all_lock_requests(locktree *lt) {
    locktree::lt_lock_request_info *info = lt->get_lock_request_info();

    // if a thread reads this bit to be true, then it should go ahead and
    // take the locktree mutex and retry lock requests. we use this bit
    // to prevent every single thread from waiting on the locktree mutex
    // in order to retry requests, especially when no requests actually exist.
    //
    // it is important to note that this bit only provides an optimization.
    // it is not problematic for it to be true when it should be false,
    // but it can be problematic for it to be false when it should be true.
    // therefore, the lock request code must ensures that when lock requests
    // are added to this locktree, the bit is set.
    // see lock_request::insert_into_lock_requests()
    if (!info->should_retry_lock_requests) {
        return;
    }

    toku_mutex_lock(&info->mutex);

    // let other threads know that they need not retry lock requests at this time.
    //
    // the motivation here is that if a bunch of threads have already released
    // their locks in the rangetree, then its probably okay for only one thread
    // to iterate over the list of requests and retry them. otherwise, at high
    // thread counts and a large number of pending lock requests, you could
    // end up wasting a lot of cycles.
    info->should_retry_lock_requests = false;

    size_t i = 0;
    while (i < info->pending_lock_requests.size()) {
        lock_request *request;
        int r = info->pending_lock_requests.fetch(i, &request);
        invariant_zero(r);

        // retry the lock request. if it didn't succeed,
        // move on to the next lock request. otherwise
        // the request is gone from the list so we may
        // read the i'th entry for the next one.
        r = request->retry();
        if (r != 0) {
            i++;
        }
    }

    // future threads should only retry lock requests if some still exist
    info->should_retry_lock_requests = info->pending_lock_requests.size() > 0;

    toku_mutex_unlock(&info->mutex);
}

// find another lock request by txnid. must hold the mutex.
lock_request *lock_request::find_lock_request(const TXNID &txnid) {
    lock_request *request;
    int r = m_info->pending_lock_requests.find_zero<TXNID, find_by_txnid>(txnid, &request, nullptr);
    if (r != 0) {
        request = nullptr;
    }
    return request;
}

// insert this lock request into the locktree's set. must hold the mutex.
void lock_request::insert_into_lock_requests(void) {
    uint32_t idx;
    lock_request *request;
    int r = m_info->pending_lock_requests.find_zero<TXNID, find_by_txnid>(m_txnid, &request, &idx);
    invariant(r == DB_NOTFOUND);
    r = m_info->pending_lock_requests.insert_at(this, idx);
    invariant_zero(r);

    // ensure that this bit is true, now that at least one lock request is in the set
    m_info->should_retry_lock_requests = true;
}

// remove this lock request from the locktree's set. must hold the mutex.
void lock_request::remove_from_lock_requests(void) {
    uint32_t idx;
    lock_request *request;
    int r = m_info->pending_lock_requests.find_zero<TXNID, find_by_txnid>(m_txnid, &request, &idx);
    invariant_zero(r && request == this);
    r = m_info->pending_lock_requests.delete_at(idx);
    invariant_zero(r);
}

int lock_request::find_by_txnid(lock_request * const &request, const TXNID &txnid) {
    TXNID request_txnid = request->m_txnid;
    if (request_txnid < txnid) {
        return -1;
    } else if (request_txnid == txnid) {
        return 0;
    } else {
        return 1;
    }
}

} /* namespace toku */