unix: avoid iterating over all async handles

include/uv-private/uv-unix.h

@@ -151,6 +151,7 @@ typedef struct {
   ngx_queue_t async_handles;                                                  \
   uv__io_t async_watcher;                                                     \
   int async_pipefd[2];                                                        \
+  volatile sig_atomic_t async_sweep_needed;                                   \
   /* RB_HEAD(uv__timers, uv_timer_s) */                                       \
   struct uv__timers {                                                         \
     struct uv_timer_s* rbh_root;                                              \

src/unix/async.c

@@ -81,11 +81,25 @@ int uv_async_send(uv_async_t* handle) {
     return 0; /* already pending */
 
   do
-    r = write(handle->loop->async_pipefd[1], "x", 1);
+    r = write(handle->loop->async_pipefd[1], &handle, sizeof(&handle));
   while (r == -1 && errno == EINTR);
 
-  if (r == -1 && errno != EAGAIN && errno != EWOULDBLOCK)
-    return uv__set_sys_error(handle->loop, errno);
+  if (r == -1) {
+    /* If pipe is full, event loop should sweep all handles */
+    if (errno == EAGAIN || errno == EWOULDBLOCK) {
+      handle->loop->async_sweep_needed = 1;
+
+      /* Pipe might be drained at this stage, which means that
+       * async_sweep_needed flag wasn't seen yet. Try writing pointer
+       * once again to ensure that pipe isn't drained yet, or to invoke
+       * uv__async_io.
+       */
+      do
+        r = write(handle->loop->async_pipefd[1], &handle, sizeof(&handle));
+      while (r == -1 && errno == EINTR);
+    } else
+      return uv__set_sys_error(handle->loop, errno);
+  }
 
   return 0;
 }
@@ -114,34 +128,75 @@ static int uv__async_init(uv_loop_t* loop) {
 }
 
 
+#define ASYNC_CB(a) \
+    if (((a)->flags & (UV_CLOSING | UV_CLOSED)) == 0 && (a)->pending) { \
+      (a)->pending = 0; \
+      (a)->async_cb((a), 0); \
+    }
+
+
 static void uv__async_io(uv_loop_t* loop, uv__io_t* handle, int events) {
   char buf[1024];
   ngx_queue_t* q;
   uv_async_t* h;
   ssize_t r;
+  ssize_t i;
+  ssize_t bytes;
+  ssize_t end;
 
+  bytes = 0;
   while (1) {
-    r = read(loop->async_pipefd[0], buf, sizeof(buf));
+    r = read(loop->async_pipefd[0], buf + bytes, sizeof(buf) - bytes);
 
-    if (r == sizeof(buf))
+    if (r == -1) {
+      if (errno == EAGAIN || errno == EWOULDBLOCK) {
+        /* Spin if there're partial data in buffer already */
+        if (bytes)
+          continue;
+        break;
+      }
+
+      if (errno == EINTR)
+        continue;
+
+      abort();
+    }
+
+    bytes += r;
+
+    /* Round up end */
+    end = (bytes / sizeof(h)) * sizeof(h);
+
+    /* If we need to sweep all handles anyway - skip this loop */
+    if (!loop->async_sweep_needed) {
+      for (i = 0; i < end; i += sizeof(h)) {
+        h = *((uv_async_t**) (buf + i));
+        ASYNC_CB(h)
+      }
+    }
+
+    bytes -= end;
+
+    /* Partial read happened */
+    if (bytes) {
+      memmove(buf, buf + end, bytes);
+      /* Spin */
       continue;
+    }
 
-    if (r != -1)
+    if (r != sizeof(buf))
       break;
-
-    if (errno == EAGAIN || errno == EWOULDBLOCK)
-      break;
-
-    if (errno == EINTR)
-      continue;
-
-    abort();
   }
 
+  /* Fast path: no sweep is required */
+  if (!loop->async_sweep_needed)
+    return;
+
+  /* Slow path: sweep all handles */
+  loop->async_sweep_needed = 0;
+
   ngx_queue_foreach(q, &loop->async_handles) {
     h = ngx_queue_data(q, uv_async_t, queue);
-    if (!h->pending) continue;
-    h->pending = 0;
-    h->async_cb(h, 0);
+    ASYNC_CB(h)
   }
 }

src/unix/loop.c

@@ -52,6 +52,7 @@ int uv__loop_init(uv_loop_t* loop, int default_loop) {
   loop->time = uv_hrtime() / 1000000;
   loop->async_pipefd[0] = -1;
   loop->async_pipefd[1] = -1;
+  loop->async_sweep_needed = 0;
   loop->signal_pipefd[0] = -1;
   loop->signal_pipefd[1] = -1;
   loop->emfile_fd = -1;