Almost everything in this test was wrong:
- race on `count = 100` in the main thread and `count++` in the
worker thread
- using volatile as atomic
- dead code after `DkThreadExit`, which is `noreturn`
- checking if noreturn function didn't actually return
- doing the above with 500 loop iterations
Move and clean up all testcases from the Pal/test directory into the
Pal/regression and add them to CI. Some of them were redundant and thus
got removed.
Now Graphene supports an improved version of DkObjectsWaitAny() with
correct polling semantics -- DkObjectsWaitEvents(). This makes
DkObjectsWaitAny() obsolete. This commit removes DkObjectsWaitAny()
and replaces it with:
- DkSynchronizationObjectWait() to wait on a single synchronization
object like mutex or event.
- DkStreamsWaitEvents() to wait on stream-like objects (this is the
renamed DkObjectsWaitEvents()).
The corresponding tests are fixed to use the new PAL interfaces.
Also, IPC helper and Async helper threads are significantly refactored
to make better use of DkStreamsWaitEvents().
When child thread exits, it wakes up its parent if CLONE_CHILD_CLEARTID was set
during clone() call. Previously, this was done by the child thread itself as
part of its own clean-up in release_clear_child_id(). But this child thread is
still alive at this point and uses some resources, most notably the stack (that
might have been provided by the parent) and the SGX TCS slot. Upon waking up,
the parent might decide to free that stack (as Pthreads do) or re-use the TCS
slot, causing data races.
This commit introduces a correct emulation of CLONE_CHILD_CLEARTID:
- A new argument `PAL_PTR clear_child_tid` is added to DkThreadExit();
it points to internal Graphene memory that is erased on child exit to notify
Async Helper thread.
- At PAL layer, when thread finally exits, it sets PAL-level *clear_child_tid = 0
(corresponds to &clear_child_tid_val_pal at LibOS level); this signals to LibOS
layer that the thread stopped using resources.
- At LibOS layer, Async Helper thread is set up to wait for the signal from
PAL; it is now the responsibility of Async Helper thread to call
release_clear_child_id() to wake up the parent thread.
- Async Helper thread waits for clear_child_tid_val_pal == 0 and then sets
the actual clear_child_tid to 0 and wakes up the waiting parent.
Note that for Linux-SGX PAL, clear_child_tid is set to 0 not immediately
but as part of handle_thread_reset, otherwise the TCS slot could be still
occupied when LibOS wakes up the parent.
As a side effect, the LibOS code for threads/process exit is cleaned up.
This commit also fixes all regression tests to use the new signature of
DkThreadExit() and increases the number of SGX threads slightly (to
accommodate the newly used Async Helper thread).
Plenty of bugfixes for Linux kernel later than 3.5 and Ubuntu later than 10.10.
More organized code to improve portability.
Regression tests for Pal to test completeness of implementation.
borysp