fd.cpp

// bthread - A M:N threading library to make applications more concurrent.
// Copyright (c) 2014 Baidu, Inc.
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//     http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Author: Ge,Jun (gejun@baidu.com)
// Date: Thu Aug  7 18:56:27 CST 2014

#include <new>                                   // std::nothrow
#include <sys/epoll.h>                           // epoll_*
#include <sys/poll.h>                            // poll()
#include "butil/atomicops.h"
#include "butil/time.h"
#include "butil/fd_utility.h"                     // make_non_blocking
#include "butil/logging.h"
#include "butil/third_party/murmurhash3/murmurhash3.h"   // fmix32
#include "bthread/butex.h"                       // butex_*
#include "bthread/task_group.h"                  // TaskGroup
#include "bthread/bthread.h"                             // bthread_start_urgent

// Implement bthread functions on file descriptors

namespace bthread {

extern BAIDU_THREAD_LOCAL TaskGroup* tls_task_group;

template <typename T, size_t NBLOCK, size_t BLOCK_SIZE>
class LazyArray {
    struct Block {
        butil::atomic<T> items[BLOCK_SIZE];
    };

public:
    LazyArray() {
        memset(_blocks, 0, sizeof(butil::atomic<Block*>) * NBLOCK);
    }

    butil::atomic<T>* get_or_new(size_t index) {
        const size_t block_index = index / BLOCK_SIZE;
        if (block_index >= NBLOCK) {
            return NULL;
        }
        const size_t block_offset = index - block_index * BLOCK_SIZE;
        Block* b = _blocks[block_index].load(butil::memory_order_consume);
        if (b != NULL) {
            return b->items + block_offset;
        }
        b = new (std::nothrow) Block;
        if (NULL == b) {
            b = _blocks[block_index].load(butil::memory_order_consume);
            return (b ? b->items + block_offset : NULL);
        }
        // Set items to default value of T.
        std::fill(b->items, b->items + BLOCK_SIZE, T());
        Block* expected = NULL;
        if (_blocks[block_index].compare_exchange_strong(
                expected, b, butil::memory_order_release,
                butil::memory_order_consume)) {
            return b->items + block_offset;
        }
        delete b;
        return expected->items + block_offset;
    }

    butil::atomic<T>* get(size_t index) const {
        const size_t block_index = index / BLOCK_SIZE;
        if (__builtin_expect(block_index < NBLOCK, 1)) {
            const size_t block_offset = index - block_index * BLOCK_SIZE;
            Block* const b = _blocks[block_index].load(butil::memory_order_consume);
            if (__builtin_expect(b != NULL, 1)) {
                return b->items + block_offset;
            }
        }
        return NULL;
    }

private:
    butil::atomic<Block*> _blocks[NBLOCK];
};

typedef butil::atomic<int> EpollButex;

static EpollButex* const CLOSING_GUARD = (EpollButex*)(intptr_t)-1L;

#ifndef NDEBUG
butil::static_atomic<int> break_nums = BASE_STATIC_ATOMIC_INIT(0);
#endif

// Able to address 67108864 file descriptors, should be enough.
LazyArray<EpollButex*, 262144/*NBLOCK*/, 256/*BLOCK_SIZE*/> fd_butexes;

static const int BTHREAD_DEFAULT_EPOLL_SIZE = 65536;

class EpollThread {
public:
    EpollThread()
        : _epfd(-1)
        , _stop(false)
        , _tid(0) {
    }

    int start(int epoll_size) {
        if (started()) {
            return -1;
        }
        _epfd = epoll_create(epoll_size);
        if (_epfd < 0) {
            PLOG(FATAL) << "Fail to epoll_create";
            return -1;
        }
        if (bthread_start_background(
                &_tid, NULL, EpollThread::run_this, this) != 0) {
            close(_epfd);
            _epfd = -1;
            LOG(FATAL) << "Fail to create epoll bthread";
            return -1;
        }
        return 0;
    }

    // Note: This function does not wake up suspended fd_wait. This is fine
    // since stop_and_join is only called on program's termination
    // (g_task_control.stop()), suspended bthreads do not block quit of
    // worker pthreads and completion of g_task_control.stop().
    int stop_and_join() {
        if (!started()) {
            return 0;
        }
        // No matter what this function returns, _epfd will be set to -1
        // (making started() false) to avoid latter stop_and_join() to
        // enter again.
        const int saved_epfd = _epfd;
        _epfd = -1;

        // epoll_wait cannot be woken up by closing _epfd. We wake up
        // epoll_wait by inserting a fd continuously triggering EPOLLOUT.
        // Visibility of _stop: constant EPOLLOUT forces epoll_wait to see
        // _stop (to be true) finally.
        _stop = true;
        int closing_epoll_pipe[2];
        if (pipe(closing_epoll_pipe)) {
            PLOG(FATAL) << "Fail to create closing_epoll_pipe";
            return -1;
        }
        epoll_event evt = { EPOLLOUT, { NULL } };
        if (epoll_ctl(saved_epfd, EPOLL_CTL_ADD,
                      closing_epoll_pipe[1], &evt) < 0) {
            PLOG(FATAL) << "Fail to add closing_epoll_pipe into epfd="
                        << saved_epfd;
            return -1;
        }

        const int rc = bthread_join(_tid, NULL);
        if (rc) {
            LOG(FATAL) << "Fail to join EpollThread, " << berror(rc);
            return -1;
        }
        close(closing_epoll_pipe[0]);
        close(closing_epoll_pipe[1]);
        close(saved_epfd);
        return 0;
    }

    int fd_wait(int fd, unsigned epoll_events, const timespec* abstime) {
        butil::atomic<EpollButex*>* p = fd_butexes.get_or_new(fd);
        if (NULL == p) {
            errno = ENOMEM;
            return -1;
        }

        EpollButex* butex = p->load(butil::memory_order_consume);
        if (NULL == butex) {
            // It is rare to wait on one file descriptor from multiple threads
            // simultaneously. Creating singleton by optimistic locking here
            // saves mutexes for each butex.
            butex = butex_create_checked<EpollButex>();
            butex->store(0, butil::memory_order_relaxed);
            EpollButex* expected = NULL;
            if (!p->compare_exchange_strong(expected, butex,
                                            butil::memory_order_release,
                                            butil::memory_order_consume)) {
                butex_destroy(butex);
                butex = expected;
            }
        }
        
        while (butex == CLOSING_GUARD) {  // bthread_close() is running.
            if (sched_yield() < 0) {
                return -1;
            }
            butex = p->load(butil::memory_order_consume);
        }
        // Save value of butex before adding to epoll because the butex may
        // be changed before butex_wait. No memory fence because EPOLL_CTL_MOD
        // and EPOLL_CTL_ADD shall have release fence.
        const int expected_val = butex->load(butil::memory_order_relaxed);

#ifdef BAIDU_KERNEL_FIXED_EPOLLONESHOT_BUG
        epoll_event evt = { epoll_events | EPOLLONESHOT, { butex } };
        if (epoll_ctl(_epfd, EPOLL_CTL_MOD, fd, &evt) < 0) {
            if (epoll_ctl(_epfd, EPOLL_CTL_ADD, fd, &evt) < 0 &&
                    errno != EEXIST) {
                PLOG(FATAL) << "Fail to add fd=" << fd << " into epfd=" << _epfd;
                return -1;
            }
        }
#else
        epoll_event evt;
        evt.events = epoll_events;
        evt.data.fd = fd;
        if (epoll_ctl(_epfd, EPOLL_CTL_ADD, fd, &evt) < 0 &&
            errno != EEXIST) {
            PLOG(FATAL) << "Fail to add fd=" << fd << " into epfd=" << _epfd;
            return -1;
        }
#endif        
        const int rc = butex_wait(butex, expected_val, abstime);
        if (rc < 0 && errno == EWOULDBLOCK) {
            // EpollThread did wake up, there's data.
            return 0;
        }
        return rc;
    }

    int fd_close(int fd) {
        if (fd < 0) {
            // what close(-1) returns
            errno = EBADF;
            return -1;
        }
        butil::atomic<EpollButex*>* pbutex = bthread::fd_butexes.get(fd);
        if (NULL == pbutex) {
            // Did not call bthread_fd functions, close directly.
            return close(fd);
        }
        EpollButex* butex = pbutex->exchange(
            CLOSING_GUARD, butil::memory_order_relaxed);
        if (butex == CLOSING_GUARD) {
            // concurrent double close detected.
            errno = EBADF;
            return -1;
        }
        if (butex != NULL) {
            butex->fetch_add(1, butil::memory_order_relaxed);
            butex_wake_all(butex);
        }
        epoll_ctl(_epfd, EPOLL_CTL_DEL, fd, NULL);
        const int rc = close(fd);
        pbutex->exchange(butex, butil::memory_order_relaxed);
        return rc;
    }

    bool started() const {
        return _epfd >= 0;
    }

private:
    static void* run_this(void* arg) {
        return static_cast<EpollThread*>(arg)->run();
    }

    void* run() {
        const int initial_epfd = _epfd;
        const size_t MAX_EVENTS = 32;
        epoll_event* e = new (std::nothrow) epoll_event[MAX_EVENTS];
        if (NULL == e) {
            LOG(FATAL) << "Fail to new epoll_event";
            return NULL;
        }

#ifndef BAIDU_KERNEL_FIXED_EPOLLONESHOT_BUG
        DLOG(INFO) << "Use DEL+ADD instead of EPOLLONESHOT+MOD due to kernel bug. Performance will be much lower.";
#endif
        while (!_stop) {
            const int epfd = _epfd;
            const int n = epoll_wait(epfd, e, MAX_EVENTS, -1);
            if (_stop) {
                break;
            }

            if (n < 0) {
                if (errno == EINTR) {
#ifndef NDEBUG
                    break_nums.fetch_add(1, butil::memory_order_relaxed);
                    int* p = &errno;
                    const char* b = berror();
                    const char* b2 = berror(errno);
                    DLOG(FATAL) << "Fail to epoll epfd=" << epfd << ", "
                                << errno << " " << p << " " <<  b << " " <<  b2;
#endif
                    continue;
                }

                PLOG(INFO) << "Fail to epoll epfd=" << epfd;
                break;
            }

#ifndef BAIDU_KERNEL_FIXED_EPOLLONESHOT_BUG
            for (int i = 0; i < n; ++i) {
                epoll_ctl(epfd, EPOLL_CTL_DEL, e[i].data.fd, NULL);
            }
#endif
            for (int i = 0; i < n; ++i) {
#ifdef BAIDU_KERNEL_FIXED_EPOLLONESHOT_BUG
                EpollButex* butex = static_cast<EpollButex*>(e[i].data.ptr);
#else
                butil::atomic<EpollButex*>* pbutex = fd_butexes.get(e[i].data.fd);
                EpollButex* butex = pbutex ?
                    pbutex->load(butil::memory_order_consume) : NULL;
#endif
                if (butex != NULL && butex != CLOSING_GUARD) {
                    butex->fetch_add(1, butil::memory_order_relaxed);
                    butex_wake_all(butex);
                }
            }
        }

        delete [] e;
        DLOG(INFO) << "EpollThread=" << _tid << "(epfd="
                   << initial_epfd << ") is about to stop";
        return NULL;
    }

    int _epfd;
    bool _stop;
    bthread_t _tid;
};

EpollThread epoll_thread[BTHREAD_EPOLL_THREAD_NUM];

static inline EpollThread& get_epoll_thread(int fd) {
    if (BTHREAD_EPOLL_THREAD_NUM == 1UL) {
        EpollThread& et = epoll_thread[0];
        et.start(BTHREAD_DEFAULT_EPOLL_SIZE);
        return et;
    }

    EpollThread& et = epoll_thread[butil::fmix32(fd) % BTHREAD_EPOLL_THREAD_NUM];
    et.start(BTHREAD_DEFAULT_EPOLL_SIZE);
    return et;
}

int stop_and_join_epoll_threads() {
    // Returns -1 if any epoll thread failed to stop.
    int rc = 0;
    for (size_t i = 0; i < BTHREAD_EPOLL_THREAD_NUM; ++i) {
        if (epoll_thread[i].stop_and_join() < 0) {
            rc = -1;
        }
    }
    return rc;
}

short epoll_to_poll_events(uint32_t epoll_events) {
    // Most POLL* and EPOLL* are same values.
    short poll_events = (epoll_events &
                         (EPOLLIN | EPOLLPRI | EPOLLOUT |
                          EPOLLRDNORM | EPOLLRDBAND |
                          EPOLLWRNORM | EPOLLWRBAND |
                          EPOLLMSG | EPOLLERR | EPOLLHUP));
    CHECK_EQ((uint32_t)poll_events, epoll_events);
    return poll_events;
}

// For pthreads.
int pthread_fd_wait(int fd, unsigned epoll_events,
                    const timespec* abstime) {
    int diff_ms = -1;
    if (abstime) {
        timespec now;
        clock_gettime(CLOCK_REALTIME, &now);
        int64_t now_us = butil::timespec_to_microseconds(now);
        int64_t abstime_us = butil::timespec_to_microseconds(*abstime);
        if (abstime_us <= now_us) {
            errno = ETIMEDOUT;
            return -1;
        }
        diff_ms = (abstime_us - now_us + 999L) / 1000L;
    }
    const short poll_events =
        bthread::epoll_to_poll_events(epoll_events);
    if (poll_events == 0) {
        errno = EINVAL;
        return -1;
    }
    pollfd ufds = { fd, poll_events, 0 };
    const int rc = poll(&ufds, 1, diff_ms);
    if (rc < 0) {
        return -1;
    }
    if (rc == 0) {
        errno = ETIMEDOUT;
        return -1;
    }
    if (ufds.revents & POLLNVAL) {
        errno = EBADF;
        return -1;
    }
    return 0;
}

}  // namespace bthread

extern "C" {

int bthread_fd_wait(int fd, unsigned epoll_events) __THROW {
    if (fd < 0) {
        errno = EINVAL;
        return -1;
    }
    bthread::TaskGroup* g = bthread::tls_task_group;
    if (NULL != g && !g->is_current_pthread_task()) {
        return bthread::get_epoll_thread(fd).fd_wait(
            fd, epoll_events, NULL);
    }
    return bthread::pthread_fd_wait(fd, epoll_events, NULL);
}

int bthread_fd_timedwait(int fd, unsigned epoll_events,
                         const timespec* abstime) __THROW {
    if (NULL == abstime) {
        return bthread_fd_wait(fd, epoll_events);
    }
    if (fd < 0) {
        errno = EINVAL;
        return -1;
    }
    bthread::TaskGroup* g = bthread::tls_task_group;
    if (NULL != g && !g->is_current_pthread_task()) {
        return bthread::get_epoll_thread(fd).fd_wait(
            fd, epoll_events, abstime);
    }
    return bthread::pthread_fd_wait(fd, epoll_events, abstime);
}

int bthread_connect(int sockfd, const sockaddr* serv_addr,
                    socklen_t addrlen) __THROW {
    bthread::TaskGroup* g = bthread::tls_task_group;
    if (NULL == g || g->is_current_pthread_task()) {
        return ::connect(sockfd, serv_addr, addrlen);
    }
    // FIXME: Scoped non-blocking?
    butil::make_non_blocking(sockfd);
    const int rc = connect(sockfd, serv_addr, addrlen);
    if (rc == 0 || errno != EINPROGRESS) {
        return rc;
    }
    if (bthread_fd_wait(sockfd, EPOLLOUT) < 0) {
        return -1;
    }
    int err;
    socklen_t errlen = sizeof(err);
    if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &err, &errlen) < 0) {
        PLOG(FATAL) << "Fail to getsockopt";
        return -1;
    }
    if (err != 0) {
        CHECK(err != EINPROGRESS);
        errno = err;
        return -1;
    }
    return 0;
}

// This does not wake pthreads calling bthread_fd_*wait.
int bthread_close(int fd) __THROW {
    return bthread::get_epoll_thread(fd).fd_close(fd);
}

}  // extern "C"