pointer to the corresponding struct thread to the thread ID (lwpid_t)
assigned to that thread. The primary reason for this change is that
libthr now internally uses the same ID as the debugger and the kernel
when referencing to a kernel thread. This allows us to implement the
support for debugging without additional translations and/or mappings.
To preserve the ABI, the 1:1 threading syscalls, including the umtx
locking API have not been changed to work on a lwpid_t. Instead the
1:1 threading syscalls operate on long and the umtx locking API has
not been changed except for the contested bit. Previously this was
the least significant bit. Now it's the most significant bit. Since
the contested bit should not be tested by userland, this change is
not expected to be visible. Just to be sure, UMTX_CONTESTED has been
removed from <sys/umtx.h>.
Reviewed by: mtm@
ABI preservation tested on: i386, ia64
followed are: Only 3 functions (pthread_cancel, pthread_setcancelstate,
pthread_setcanceltype) are required to be async-signal-safe by POSIX. None of
the rest of the pthread api is required to be async-signal-safe. This means
that only the three mentioned functions are safe to use from inside
signal handlers.
However, there are certain system/libc calls that are
cancellation points that a caller may call from within a signal handler,
and since they are cancellation points calls have to be made into libthr
to test for cancellation and exit the thread if necessary. So, the
cancellation test and thread exit code paths must be async-signal-safe
as well. A summary of the changes follows:
o Almost all of the code paths that masked signals, as well as locking the
pthread structure now lock only the pthread structure.
o Signals are masked (and left that way) as soon as a thread enters
pthread_exit().
o The active and dead threads locks now explicitly require that signals
are masked.
o Access to the isdead field of the pthread structure is protected by both
the active and dead list locks for writing. Either one is sufficient for
reading.
o The thread state and type fields have been combined into one three-state
switch to make it easier to read without requiring a lock. It doesn't need
a lock for writing (and therefore for reading either) because only the
current thread can write to it and it is an integer value.
o The thread state field of the pthread structure has been eliminated. It
was an unnecessary field that mostly duplicated the flags field, but
required additional locking that would make a lot more code paths require
signal masking. Any truly unique values (such as PS_DEAD) have been
reborn as separate members of the pthread structure.
o Since the mutex and condvar pthread functions are not async-signal-safe
there is no need to muck about with the wait queues when handling
a signal ...
o ... which also removes the need for wrapping signal handlers and sigaction(2).
o The condvar and mutex async-cancellation code had to be revised as a result
of some of these changes, which resulted in semi-unrelated changes which
would have been difficult to work on as a separate commit, so they are
included as well.
The only part of the changes I am worried about is related to locking for
the pthread joining fields. But, I will take a closer look at them once this
mega-patch is committed.
o Remove some code duplication between _thread_init(), which is run once
to initialize libthr and the intitial thread, and pthread_create(), which
initializes newly created threads, into a new function called from both
places: init_td_common()
o Move initialization of certain parts of libthr into a separate
function. These include:
- Active threads list and it's lock
- Dead threads list and it's lock & condition variable
- Naming and insertion of the initial thread into the
active threads list.
problems: (1) The wrong flag was being checked for in the attribute
(2) The pthread's state was not being set to indicate it was
suspended.
Noticed by: Igor Sysoev <is@rambler-co.ru>
Modify the thread creation and thread searching routine
to lock the thread lists with the new locks instead of GIANT_LOCK.
Approved by: re/blanket libthr
as curthread in the new context, so that it will be set automatically when
the thread is switched to. This fixes a race where we'd run for a little
while with curthread unset in _thread_start.
Reviewed by: jeff
_get_curthread(). This is similar to the kernel's curthread. Doing
this saves stack overhead and is more convenient to the programmer.
- Pass the pointer to the newly created thread to _thread_init().
- Remove _get_curthread_slow().
