Commit Graph

8 Commits

Author SHA1 Message Date
Peter Wemm
7f3dea244c $Id$ -> $FreeBSD$ 1999-08-28 00:22:10 +00:00
Daniel Eischen
fa7c4d5575 Add RCS IDs to those files without them.
Fix copyrights (s/REGENTS/AUTHOR).

Suggested by:	tg
Approved by:	jb
1999-08-05 12:15:30 +00:00
John Birrell
02292f131a In the words of the author:
o The polling mechanism for I/O readiness was changed from
    select() to poll().  In additon, a wrapped version of poll()
    is now provided.

  o The wrapped select routine now converts each fd_set to a
    poll array so that the thread scheduler doesn't have to
    perform a bitwise search for selected fds each time file
    descriptors are polled for I/O readiness.

  o The thread scheduler was modified to use a new queue (_workq)
    for threads that need work.  Threads waiting for I/O readiness
    and spinblocks are added to the work queue in addition to the
    waiting queue.  This reduces the time spent forming/searching
    the array of file descriptors being polled.

  o The waiting queue (_waitingq) is now maintained in order of
    thread wakeup time.  This allows the thread scheduler to
    find the nearest wakeup time by looking at the first thread
    in the queue instead of searching the entire queue.

  o Removed file descriptor locking for select/poll routines.  An
    application should not rely on the threads library for providing
    this locking; if necessary, the application should use mutexes
    to protect selecting/polling of file descriptors.

  o Retrieve and use the kernel clock rate/resolution at startup
    instead of hardcoding the clock resolution to 10 msec (tested
    with kernel running at 1000 HZ).

  o All queues have been changed to use queue.h macros.  These
    include the queues of all threads, dead threads, and threads
    waiting for file descriptor locks.

  o Added reinitialization of the GC mutex and condition variable
    after a fork.  Also prevented reallocation of the ready queue
    after a fork.

  o Prevented the wrapped close routine from closing the thread
    kernel pipes.

  o Initialized file descriptor table for stdio entries at thread
    init.

  o Provided additional flags to indicate to what queues threads
    belong.

  o Moved TAILQ initialization for statically allocated mutex and
    condition variables to after the spinlock.

  o Added dispatching of signals to pthread_kill.  Removing the
    dispatching of signals from thread activation broke sigsuspend
    when pthread_kill was used to send a signal to a thread.

  o Temporarily set the state of a thread to PS_SUSPENDED when it
    is first created and placed in the list of threads so that it
    will not be accidentally scheduled before becoming a member
    of one of the scheduling queues.

  o Change the signal handler to queue signals to the thread kernel
    pipe if the scheduling queues are protected.  When scheduling
    queues are unprotected, signals are then dequeued and handled.

  o Ensured that all installed signal handlers block the scheduling
    signal and that the scheduling signal handler blocks all
    other signals.  This ensures that the signal handler is only
    interruptible for and by non-scheduling signals.  An atomic
    lock is used to decide which instance of the signal handler
    will handle pending signals.

  o Removed _lock_thread_list and _unlock_thread_list as they are
    no longer used to protect the thread list.

  o Added missing RCS IDs to modified files.

  o Added checks for appropriate queue membership and activity when
    adding, removing, and searching the scheduling queues.  These
    checks add very little overhead and are enabled when compiled
    with _PTHREADS_INVARIANTS defined.  Suggested and implemented
    by Tor Egge with some modification by me.

  o Close a race condition in uthread_close.  (Tor Egge)

  o Protect the scheduling queues while modifying them in
    pthread_cond_signal and _thread_fd_unlock.  (Tor Egge)

  o Ensure that when a thread gets a mutex, the mutex is on that
    threads list of owned mutexes.  (Tor Egge)

  o Set the kernel-in-scheduler flag in _thread_kern_sched_state
    and _thread_kern_sched_state_unlock to prevent a scheduling
    signal from calling the scheduler again.  (Tor Egge)

  o Don't use TAILQ_FOREACH macro while searching the waiting
    queue for threads in a sigwait state, because a change of
    state destroys the TAILQ link.  It is actually safe to do
    so, though, because once a sigwaiting thread is found, the
    loop ends and the function returns.  (Tor Egge)

  o When dispatching signals to threads, make the thread inherit
    the signal deferral flag of the currently running thread.
    (Tor Egge)

Submitted by: Daniel Eischen <eischen@vigrid.com> and
              Tor Egge <Tor.Egge@fast.no>
1999-06-20 08:28:48 +00:00
John Birrell
58a7cc5d1b [ The author's description... ]
o Runnable threads are now maintained in priority queues.  The
    implementation requires two things:

      1.) The priority queues must be protected during insertion
          and removal of threads.  Since the kernel scheduler
          must modify the priority queues, a spinlock for
          protection cannot be used.   The functions
          _thread_kern_sched_defer() and _thread_kern_sched_undefer()
          were added to {un}defer kernel scheduler activation.

      2.) A thread (active) priority change can be performed only
          when the thread is removed from the priority queue.  The
          implementation uses a threads active priority when
          inserting it into the queue.

    A by-product is that thread switches are much faster.  A
    separate queue is used for waiting and/or blocked threads,
    and it is searched at most 2 times in the kernel scheduler
    when there are active threads.  It should be possible to
    reduce this to once by combining polling of threads waiting
    on I/O with the loop that looks for timed out threads and
    the minimum timeout value.

  o Functions to defer kernel scheduler activation were added.  These
    are _thread_kern_sched_defer() and _thread_kern_sched_undefer()
    and may be called recursively.  These routines do not block the
    scheduling signal, but latch its occurrence.  The signal handler
    will not call the kernel scheduler when the running thread has
    deferred scheduling, but it will be called when running thread
    undefers scheduling.

  o Added support for _POSIX_THREAD_PRIORITY_SCHEDULING.  All the
    POSIX routines required by this should now be implemented.
    One note, SCHED_OTHER, SCHED_FIFO, and SCHED_RR are required
    to be defined by including pthread.h.  These defines are currently
    in sched.h.  I modified pthread.h to include sched.h but don't
    know if this is the proper thing to do.

  o Added support for priority protection and inheritence mutexes.
    This allows definition of _POSIX_THREAD_PRIO_PROTECT and
    _POSIX_THREAD_PRIO_INHERIT.

  o Added additional error checks required by POSIX for mutexes and
    condition variables.

  o Provided a wrapper for sigpending which is marked as a hidden
    syscall.

  o Added a non-portable function as a debugging aid to allow an
    application to monitor thread context switches.  An application
    can install a routine that gets called everytime a thread
    (explicitly created by the application) gets context switched.
    The routine gets passed the pthread IDs of the threads that are
    being switched in and out.

Submitted by: Dan Eischen <eischen@vigrid.com>

Changes by me:

  o Added a PS_SPINBLOCK state to deal with the priority inversion
    problem most often (I think) seen by threads calling malloc/free/realloc.

  o Dispatch signals to the running thread directly rather than at a
    context switch to avoid the situation where the switch never occurs.
1999-03-23 05:07:56 +00:00
John Birrell
5f867deba5 Don't automatically restart syscalls for the signals that the thread
kernel needs.
1998-08-26 20:55:31 +00:00
John Birrell
4a027d50c7 Change signal model to match POSIX (i.e. one set of signal handlers
for the process, not a separate set for each thread). By default, the
process now only has signal handlers installed for SIGVTALRM, SIGINFO
and SIGCHLD. The thread kernel signal handler is installed for other
signals on demand. This means that SIG_IGN and SIG_DFL processing is now
left to the kernel, not the thread kernel.

Change the signal dispatch to no longer use a signal thread, and
call the signal handler using the stack of the thread that has the
signal pending.

Change the atomic lock method to use test-and-set asm code with
a yield if blocked. This introduces separate locks for each type
of object instead of blocking signals to prevent a context
switch. It was this blocking of signals that caused the performance
degradation the people have noted.

This is a *big* change!
1998-04-29 09:59:34 +00:00
Julian Elischer
c840cec7c5 Submitted by: John Birrell
uthreads update from the author.
1997-02-05 23:26:09 +00:00
Julian Elischer
012dfd00b3 Reviewed by: julian
Submitted by:	 john birrel

One version of the pthreads library
another will follow with differnt actions under some cases..
not QUITE complete
1996-01-22 00:23:58 +00:00