Event loop basics + libuv

libs/libuv/src/unix/linux-inotify.c

@@ -0,0 +1,285 @@
+/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
+ * 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 "uv.h"
+#include "tree.h"
+#include "internal.h"
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <errno.h>
+
+#include <sys/types.h>
+#include <unistd.h>
+
+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)
+
+
+static void uv__inotify_read(uv_loop_t* loop,
+                             uv__io_t* w,
+                             unsigned int revents);
+
+
+static int new_inotify_fd(void) {
+  int err;
+  int fd;
+
+  fd = uv__inotify_init1(UV__IN_NONBLOCK | UV__IN_CLOEXEC);
+  if (fd != -1)
+    return fd;
+
+  if (errno != ENOSYS)
+    return -errno;
+
+  fd = uv__inotify_init();
+  if (fd == -1)
+    return -errno;
+
+  err = uv__cloexec(fd, 1);
+  if (err == 0)
+    err = uv__nonblock(fd, 1);
+
+  if (err) {
+    uv__close(fd);
+    return err;
+  }
+
+  return fd;
+}
+
+
+static int init_inotify(uv_loop_t* loop) {
+  int err;
+
+  if (loop->inotify_fd != -1)
+    return 0;
+
+  err = new_inotify_fd();
+  if (err < 0)
+    return err;
+
+  loop->inotify_fd = err;
+  uv__io_init(&loop->inotify_read_watcher, uv__inotify_read, loop->inotify_fd);
+  uv__io_start(loop, &loop->inotify_read_watcher, POLLIN);
+
+  return 0;
+}
+
+
+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);
+}
+
+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);
+    uv__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 uv__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 uv__inotify_event*)p;
+
+      events = 0;
+      if (e->mask & (UV__IN_ATTRIB|UV__IN_MODIFY))
+        events |= UV_CHANGE;
+      if (e->mask & ~(UV__IN_ATTRIB|UV__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.
+       */
+      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);
+
+        h->cb(h, path, events, 0);
+      }
+      /* done iterating, time to (maybe) free empty watcher_list */
+      w->iterating = 0;
+      maybe_free_watcher_list(w, loop);
+    }
+  }
+}
+
+
+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;
+}
+
+
+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;
+  int events;
+  int err;
+  int wd;
+
+  if (uv__is_active(handle))
+    return -EINVAL;
+
+  err = init_inotify(handle->loop);
+  if (err)
+    return err;
+
+  events = UV__IN_ATTRIB
+         | UV__IN_CREATE
+         | UV__IN_MODIFY
+         | UV__IN_DELETE
+         | UV__IN_DELETE_SELF
+         | UV__IN_MOVE_SELF
+         | UV__IN_MOVED_FROM
+         | UV__IN_MOVED_TO;
+
+  wd = uv__inotify_add_watch(handle->loop->inotify_fd, path, events);
+  if (wd == -1)
+    return -errno;
+
+  w = find_watcher(handle->loop, wd);
+  if (w)
+    goto no_insert;
+
+  w = uv__malloc(sizeof(*w) + strlen(path) + 1);
+  if (w == NULL)
+    return -ENOMEM;
+
+  w->wd = wd;
+  w->path = strcpy((char*)(w + 1), path);
+  QUEUE_INIT(&w->watchers);
+  w->iterating = 0;
+  RB_INSERT(watcher_root, CAST(&handle->loop->inotify_watchers), w);
+
+no_insert:
+  uv__handle_start(handle);
+  QUEUE_INSERT_TAIL(&w->watchers, &handle->watchers);
+  handle->path = w->path;
+  handle->cb = cb;
+  handle->wd = wd;
+
+  return 0;
+}
+
+
+int uv_fs_event_stop(uv_fs_event_t* handle) {
+  struct watcher_list* w;
+
+  if (!uv__is_active(handle))
+    return 0;
+
+  w = find_watcher(handle->loop, handle->wd);
+  assert(w != NULL);
+
+  handle->wd = -1;
+  handle->path = NULL;
+  uv__handle_stop(handle);
+  QUEUE_REMOVE(&handle->watchers);
+
+  maybe_free_watcher_list(w, handle->loop);
+
+  return 0;
+}
+
+
+void uv__fs_event_close(uv_fs_event_t* handle) {
+  uv_fs_event_stop(handle);
+}