tests: add test-compositor

This patch introduces a set of functions that can create a display
and clients for tests.
On server side the user can use functions:
  display_create()
  display_destroy()
  create_client()
  display_run()
  display_resume()
and on client side the user can use:
  client_connect()
  client_disconnect()
  stop_display()

The stop_display() and display_resume() are functions that serve as a barrier
and also allow the display to take some action after the display_run() was called,
because after the display is stopped, it can run arbitrary code until it calls
display_resume().

client_connect() function connects to wayland display and creates a proxy to
test_compositor global object, so it can ask for stopping the display later
using stop_display().

An example:

  void
  client_main()
  {
        /* or client can use wl_display_connect(NULL)
         * and do all the stuff manually */
        struct client *c = client_connect();

        /* do some stuff, ... */

        /* stop the display so that it can
         * do some other stuff */
        stop_display(c, 1);

        /* ... */

        client_disconnect(c);
  }

  TEST(dummy_tst)
  {
       struct display *d = display_create();

       /* set up the display */
       wl_global_create(d->wl_display, ...);

       /* ... */

       create_client(d, client_main);
       display_run();

       /* if we are here, the display has been stopped
        * and we can do some code, i. e. create another global or so */
       wl_global_create(d->wl_display, ...);

       /* ... */

       display_resume(d); /* resume display and clients */

       display_destroy(d);
  }

v2:
  added/changed message in few asserts that were not clear
  fixed codying style issues and typo
  client_create_with_name: fixed a condition in an assert
  get_socket_name: use also pid
  check_error: fix errno -> err

[Pekka Paalanen: added test-compositor.h to SOURCES, added
WL_HIDE_DEPRECATED to get rid of deprecated defs and lots of warnings,
fixed one unchecked return value from write().]

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
tests: use test compositor in queue-test

Most of the code of the queue-test is covered by the test compositor,
so we can save few lines and use the test compositor instead.
I think it's also more readable.

This patch removes timeout from the test. We plan to add timeout
to all tests later, though.

v2.
  rebased to master

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
tests: test posting errors

Test posting errors to one and more clients.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
tests: test if thread can block on error

wl_display_read_events() can make a thread wait until some other thread
ends reading. Normally it wakes up all threads after the reading is
done. But there's a place when it does not get to waking up the threads
- when an error occurs. This test reveals bug that can block programs.

If a thread is waiting in wl_display_read_events() and another thread
calls wl_display_read_events and the reading fails,
then the sleeping thread is not woken up. This is because
display_handle_error is using old pthread_cond instead of new
display->reader_cond, that was added along with wl_display_read_events().

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
tests: add tests for wl_display_cancel_read

Test if wl_display_cancel_read wakes up other threads.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
tests: add test for reading after an error occurred

This test shows that it's possible to successfully call wl_display_prepare_read
and wl_display_read_events after an error occurred. That may lead to
deadlock.

When you call prepare read from two threads and then call read_events,
one thread gets sleeping. The call from the other thread will return -1 and invokes
display_fatal_error, but since
we have display->last_error already set, the broadcast is not called and
the sleeping thread sleeps indefinitely.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
client: check for error before prepare/read

This prevents from blocking shown in one display test. Also, it
makes sense to not proceed further in the code of these function
when an error occurred.

v2. set errno
    put note about the errno into doc
    check for error with mutex locked

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>