libuv源码阅读(12)--change

#include <stdio.h>
#include <stdlib.h>

#include <uv.h>

uv_loop_t *loop;
const char *command;

void run_command(uv_fs_event_t *handle, const char *filename, int events, int status) {
    char path[1024];
    size_t size = 1023;
    // Does not handle error if path is longer than 1023.
    uv_fs_event_getpath(handle, path, &size);
    path[size] = '\0';

    fprintf(stderr, "Change detected in %s: ", path);
    if (events & UV_RENAME)
        fprintf(stderr, "renamed");
    if (events & UV_CHANGE)
        fprintf(stderr, "changed");

    fprintf(stderr, " %s\n", filename ? filename : "");
    system(command);
}

int main(int argc, char **argv) {
    if (argc <= 2) {
        fprintf(stderr, "Usage: %s <command> <file1> [file2 ...]\n", argv[0]);
        return 1;
    }

    loop = uv_default_loop();
    command = argv[1];

    while (argc-- > 2) {
        fprintf(stderr, "Adding watch on %s\n", argv[argc]);
        uv_fs_event_t *fs_event_req = malloc(sizeof(uv_fs_event_t));
        uv_fs_event_init(loop, fs_event_req);
        // The recursive flag watches subdirectories too.
        uv_fs_event_start(fs_event_req, run_command, argv[argc], UV_FS_EVENT_RECURSIVE);
    }

    return uv_run(loop, UV_RUN_DEFAULT);
}

struct uv_fs_event_s {
  UV_HANDLE_FIELDS
  /* private */
  char* path;
  UV_FS_EVENT_PRIVATE_FIELDS
};

#define UV_HANDLE_FIELDS                                                      \
  /* public */                                                                \
  void* data;                                                                 \
  /* read-only */                                                             \
  uv_loop_t* loop;                                                            \
  uv_handle_type type;                                                        \
  /* private */                                                               \
  uv_close_cb close_cb;                                                       \
  void* handle_queue[2];                                                      \
  union {                                                                     \
    int fd;                                                                   \
    void* reserved[4];                                                        \
  } u;                                                                        \
  UV_HANDLE_PRIVATE_FIELDS                                                    \

#define UV_HANDLE_PRIVATE_FIELDS                                              \
  uv_handle_t* next_closing;                                                  \
  unsigned int flags;                                                         \

#define UV_FS_EVENT_PRIVATE_FIELDS                                            \
  uv_fs_event_cb cb;                                                          \
  UV_PLATFORM_FS_EVENT_FIELDS                                                 \

#define UV_PLATFORM_FS_EVENT_FIELDS                                           \
  void* watchers[2];                                                          \
  int wd;                                                                     \

int uv_fs_event_init(uv_loop_t* loop, uv_fs_event_t* handle) {
  uv__handle_init(loop, (uv_handle_t*)handle, UV_FS_EVENT);
  return 0;
}

#define uv__handle_init(loop_, h, type_)                                      \
  do {                                                                        \
    (h)->loop = (loop_);                                                      \
    (h)->type = (type_);                                                      \
    (h)->flags = UV_HANDLE_REF;  /* Ref the loop when active. */              \
    QUEUE_INSERT_TAIL(&(loop_)->handle_queue, &(h)->handle_queue);            \
    uv__handle_platform_init(h);                                              \
  }                                                                           \
  while (0)

struct watcher_list {
  RB_ENTRY(watcher_list) entry;
  QUEUE watchers;
  int iterating;
  char* path;
  int wd;
};

struct watcher_root {
  struct watcher_list* rbh_root;
};
#define CAST(p) ((struct watcher_root*)(p))


static int compare_watchers(const struct watcher_list* a,
                            const struct watcher_list* b) {
  if (a->wd < b->wd) return -1;
  if (a->wd > b->wd) return 1;
  return 0;
}


RB_GENERATE_STATIC(watcher_root, watcher_list, entry, compare_watchers)

int uv_fs_event_start(uv_fs_event_t* handle,
                      uv_fs_event_cb cb,
                      const char* path,
                      unsigned int flags) {
  struct watcher_list* w;
  size_t len;
  int events;
  int err;
  int wd;

  if (uv__is_active(handle))
    return UV_EINVAL;

  // 初始化linux下 inotify_init1创造的文件监听fd 绑定对应io 回调 激活对应的 loop->inotify_read_watche
  err = init_inotify(handle->loop);
  if (err)
    return err;

  events = IN_ATTRIB
         | IN_CREATE
         | IN_MODIFY
         | IN_DELETE
         | IN_DELETE_SELF
         | IN_MOVE_SELF
         | IN_MOVED_FROM
         | IN_MOVED_TO;

  // 监听fd上指定的事件
  wd = inotify_add_watch(handle->loop->inotify_fd, path, events);
  if (wd == -1)
    return UV__ERR(errno);

  // 红黑树查找是否之前已经插入过了 因为一个 wd对应的 wathcer可以绑定多个handle
  w = find_watcher(handle->loop, wd);
  if (w)
    goto no_insert;

  len = strlen(path) + 1;
  w = uv__malloc(sizeof(*w) + len);
  if (w == NULL)
    return UV_ENOMEM;

  w->wd = wd;
  // 这一行代码很有意思 大家细品 w地址+1 指针偏移量刚好跨过 wathcer 结构体到达 存放path的位置 实在是秒啊
  w->path = memcpy(w + 1, path, len);
  QUEUE_INIT(&w->watchers);
  w->iterating = 0;
  // 插入新的watche
  RB_INSERT(watcher_root, CAST(&handle->loop->inotify_watchers), w);

no_insert:
  // 激活handle
  uv__handle_start(handle);
  QUEUE_INSERT_TAIL(&w->watchers, &handle->watchers);
  // 绑定关键信息
  handle->path = w->path;
  handle->cb = cb;
  handle->wd = wd;

  return 0;
}


static int init_inotify(uv_loop_t* loop) {
  int fd;

  if (loop->inotify_fd != -1)
    return 0;

  fd = inotify_init1(IN_NONBLOCK | IN_CLOEXEC);
  if (fd < 0)
    return UV__ERR(errno);

  loop->inotify_fd = fd;
  uv__io_init(&loop->inotify_read_watcher, uv__inotify_read, loop->inotify_fd);
  uv__io_start(loop, &loop->inotify_read_watcher, POLLIN);

  return 0;
}

// 红黑树中根据 wd 查找对应的watche
static struct watcher_list* find_watcher(uv_loop_t* loop, int wd) {
  struct watcher_list w;
  w.wd = wd;
  return RB_FIND(watcher_root, CAST(&loop->inotify_watchers), &w);
}

// 如果watcher的观察者数组没有了 就可以把它从红黑树中移除了 同时把它从文件监听fd中移除
static void maybe_free_watcher_list(struct watcher_list* w, uv_loop_t* loop) {
  /* if the watcher_list->watchers is being iterated over, we can't free it. */
  if ((!w->iterating) && QUEUE_EMPTY(&w->watchers)) {
    /* No watchers left for this path. Clean up. */
    RB_REMOVE(watcher_root, CAST(&loop->inotify_watchers), w);
    inotify_rm_watch(loop->inotify_fd, w->wd);
    uv__free(w);
  }
}

static void uv__inotify_read(uv_loop_t* loop,
                             uv__io_t* dummy,
                             unsigned int events) {
  const struct inotify_event* e;
  struct watcher_list* w;
  uv_fs_event_t* h;
  QUEUE queue;
  QUEUE* q;
  const char* path;
  ssize_t size;
  const char *p;
  /* needs to be large enough for sizeof(inotify_event) + strlen(path) */
  char buf[4096];

  while (1) {
    do
      size = read(loop->inotify_fd, buf, sizeof(buf));
    while (size == -1 && errno == EINTR);

    if (size == -1) {
      assert(errno == EAGAIN || errno == EWOULDBLOCK);
      break;
    }

    assert(size > 0); /* pre-2.6.21 thing, size=0 == read buffer too small */

    /* Now we have one or more inotify_event structs. */
    for (p = buf; p < buf + size; p += sizeof(*e) + e->len) {
      e = (const struct inotify_event*) p;

      events = 0;
      if (e->mask & (IN_ATTRIB|IN_MODIFY))
        events |= UV_CHANGE;
      if (e->mask & ~(IN_ATTRIB|IN_MODIFY))
        events |= UV_RENAME;

      w = find_watcher(loop, e->wd);
      if (w == NULL)
        continue; /* Stale event, no watchers left. */

      /* inotify does not return the filename when monitoring a single file
       * for modifications. Repurpose the filename for API compatibility.
       * I'm not convinced this is a good thing, maybe it should go.
       */
      path = e->len ? (const char*) (e + 1) : uv__basename_r(w->path);

      /* We're about to iterate over the queue and call user's callbacks.
       * What can go wrong?
       * A callback could call uv_fs_event_stop()
       * and the queue can change under our feet.
       * So, we use QUEUE_MOVE() trick to safely iterate over the queue.
       * And we don't free the watcher_list until we're done iterating.
       *
       * First,
       * tell uv_fs_event_stop() (that could be called from a user's callback)
       * not to free watcher_list.
       */
      // 开始着手处理这个wd对应的观察者上所有watchers
      w->iterating = 1;
      QUEUE_MOVE(&w->watchers, &queue);
      while (!QUEUE_EMPTY(&queue)) {
        q = QUEUE_HEAD(&queue);
        h = QUEUE_DATA(q, uv_fs_event_t, watchers);

        QUEUE_REMOVE(q);
        QUEUE_INSERT_TAIL(&w->watchers, q);

        // 执行用户回调
        h->cb(h, path, events, 0);
      }
      /* done iterating, time to (maybe) free empty watcher_list */
      w->iterating = 0;
      maybe_free_watcher_list(w, loop);
    }
  }
}