dir_watch_inotify.cpp

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/* Copyright (c) 2012 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include "precompiled.h"

#include "lib/sysdep/dir_watch.h"
#include "lib/sysdep/sysdep.h"
#include "ps/CLogger.h"

#include <map>
#include <string>
#include <sys/inotify.h>


struct NotificationEvent
{
    std::string filename;
    uint32_t code;
    int wd;
};

// To avoid deadlocks and slow synchronous reads, it's necessary to use a
// separate thread for reading events from inotify.
// So we just spawn a thread to push events into this list, then swap it out
// when someone calls dir_watch_Poll.
// (We assume STL memory allocation is thread-safe.)
static std::vector<NotificationEvent> g_notifications;
static pthread_t g_event_loop_thread;

// Mutex must wrap all accesses of g_notifications
// while the event loop thread is running
static pthread_mutex_t g_mutex = PTHREAD_MUTEX_INITIALIZER;

// trool; -1 = init failed and all operations will be aborted silently.
// this is so that each dir_* call doesn't complain if the system's
// inotify is broken or unavailable.
static int initialized = 0;

// Inotify file descriptor
static int inotifyfd;
 
// With inotify, using a map seems to be a good alternative to FAM's userdata
typedef std::map<int, PDirWatch> DirWatchMap;
static DirWatchMap g_paths;

struct DirWatch
{
    DirWatch()
        : reqnum(-1)
    {
    }

    ~DirWatch()
    {
        ENSURE(initialized > 0);
        inotify_rm_watch(inotifyfd, reqnum);
    }

    OsPath path;
    int reqnum;
};

// for atexit
static void inotify_deinit()
{
    close(inotifyfd);

    pthread_cancel(g_event_loop_thread);
    // NOTE: POSIX threads are (by default) only cancellable inside particular
    // functions (like 'select'), so this should safely terminate while it's
    // in select/etc (and won't e.g. cancel while it's holding the
    // mutex)

    // Wait for the thread to finish
    pthread_join(g_event_loop_thread, NULL);
}

static void inotify_event_loop_process_events()
{
    // Buffer for reading the events.
    // Need to be careful about overflow here.
    char buffer[65535];

    // Event iterator
    ssize_t buffer_i = 0;

    // Total size of all the events
    ssize_t r;

    // Size & struct for the current event
    size_t event_size;
    struct inotify_event *pevent;

    r = read(inotifyfd, buffer, 65535);
    if(r <= 0)
        return;

    while(buffer_i < r)
    {
        NotificationEvent ne;
        pevent = (struct inotify_event *) &buffer[buffer_i];

        event_size = offsetof(struct inotify_event, name) + pevent->len;
        ne.wd = pevent->wd;
        ne.filename = pevent->name;
        ne.code = pevent->mask;

        pthread_mutex_lock(&g_mutex);
        g_notifications.push_back(ne);
        pthread_mutex_unlock(&g_mutex);

        buffer_i += event_size;
    }
}

static void* inotify_event_loop(void*)
{
    while(true)
    {
        fd_set fdrset;
        FD_ZERO(&fdrset);
        FD_SET(inotifyfd, &fdrset);
        errno = 0;
        // Block with select until there's events waiting
        while(select(inotifyfd+1, &fdrset, NULL, NULL, NULL) < 0)
        {
            if(errno == EINTR)
            {
                // interrupted - try again
                FD_ZERO(&fdrset);
                FD_SET(inotifyfd, &fdrset);
            }
            else if(errno == EBADF)
            {
                // probably just lost the connection to inotify - kill the thread
                debug_printf(L"inotify_event_loop: Invalid file descriptor inotifyfd=%d\n", inotifyfd);
                return NULL;
            }
            else
            {
                // oops
                debug_printf(L"inotify_event_loop: select error errno=%d\n", errno);
                return NULL;
            }
            errno = 0;
        }
        if(FD_ISSET(inotifyfd, &fdrset))
            inotify_event_loop_process_events();
    }
}

Status dir_watch_Add(const OsPath& path, PDirWatch& dirWatch)
{
    char resolved[PATH_MAX + 1];

    // init already failed; don't try again or complain 
    if(initialized == -1)
        return ERR::FAIL;   // NOWARN

    if(!initialized)
    {
        errno = 0;
        if((inotifyfd = inotify_init()) < 0) 
        {
            // Check for error ?
            int err = errno;
            initialized = -1;
            LOGERROR(L"Error initializing inotify file descriptor; hotloading will be disabled, errno=%d", err);
            errno = err;
            return StatusFromErrno();   // NOWARN
        }

        errno = 0;
        int ret = pthread_create(&g_event_loop_thread, NULL, &inotify_event_loop, NULL);
        if (ret != 0)
        {
            initialized = -1;
            LOGERROR(L"Error creating inotify event loop thread; hotloading will be disabled, err=%d", ret);
            errno = ret;
            return StatusFromErrno();   // NOWARN
        }

        initialized = 1;
        atexit(inotify_deinit);
    }

    PDirWatch tmpDirWatch(new DirWatch);
    errno = 0;
    int wd = inotify_add_watch(inotifyfd, realpath(OsString(path).c_str(), resolved), IN_CREATE | IN_DELETE | IN_CLOSE_WRITE);
    if (wd < 0)
        WARN_RETURN(StatusFromErrno());

    dirWatch.swap(tmpDirWatch);
    dirWatch->path = path;
    dirWatch->reqnum = wd;
    g_paths.insert(std::make_pair(wd, dirWatch));

    return INFO::OK;
}

Status dir_watch_Poll(DirWatchNotifications& notifications)
{
    if(initialized == -1)
        return ERR::FAIL;   // NOWARN
    if(!initialized) // XXX Fix Atlas instead of suppressing the warning
        return ERR::FAIL; //WARN_RETURN(ERR::LOGIC);

    std::vector<NotificationEvent> polled_notifications;

    pthread_mutex_lock(&g_mutex);
    g_notifications.swap(polled_notifications);
    pthread_mutex_unlock(&g_mutex);

    for(size_t i = 0; i < polled_notifications.size(); ++i)
    {
        DirWatchNotification::EType type;
        // TODO: code is actually a bitmask, so this is slightly incorrect
        switch(polled_notifications[i].code)
        {
        case IN_CLOSE_WRITE:
            type = DirWatchNotification::Changed;
            break;
        case IN_CREATE:
            type = DirWatchNotification::Created;
            break;
        case IN_DELETE:
            type = DirWatchNotification::Deleted;
            break;
        default:
            continue;
        }

        DirWatchMap::iterator it = g_paths.find(polled_notifications[i].wd);
        if(it != g_paths.end())
        {
            OsPath filename = Path(OsString(it->second->path).append(polled_notifications[i].filename));
            notifications.push_back(DirWatchNotification(filename, type));
        }
        else
        {
            debug_printf(L"dir_watch_Poll: Notification with invalid watch descriptor wd=%d\n", polled_notifications[i].wd);
        }
    }

    // nothing new; try again later
    return INFO::OK;
}