1.0.26.5: improve CONDITION-WAIT, RELEASE-MUTEX

[sbcl.git] / src / code / target-thread.lisp

;;;; support for threads in the target machine

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!THREAD")

;;; Of the WITH-PINNED-OBJECTS in this file, not every single one is
;;; necessary because threads are only supported with the conservative
;;; gencgc and numbers on the stack (returned by GET-LISP-OBJ-ADDRESS)
;;; are treated as references.

;;; set the doc here because in early-thread FDOCUMENTATION is not
;;; available, yet
#!+sb-doc
(setf (fdocumentation '*current-thread* 'variable)
      "Bound in each thread to the thread itself.")

(defstruct (thread (:constructor %make-thread))
  #!+sb-doc
  "Thread type. Do not rely on threads being structs as it may change
in future versions."
  name
  %alive-p
  os-thread
  interruptions
  (interruptions-lock (make-mutex :name "thread interruptions lock"))
  result
  (result-lock (make-mutex :name "thread result lock")))

#!+sb-doc
(setf (fdocumentation 'thread-name 'function)
      "The name of the thread. Setfable.")

(def!method print-object ((thread thread) stream)
  (print-unreadable-object (thread stream :type t :identity t)
    (let* ((cookie (list thread))
           (info (if (thread-alive-p thread)
                     :running
                     (multiple-value-list
                      (join-thread thread :default cookie))))
           (state (if (eq :running info)
                      info
                      (if (eq cookie (car info))
                          :aborted
                          :finished)))
           (values (when (eq :finished state) info)))
      (format stream
              "~@[~S ~]~:[~A~;~A~:[ no values~; values: ~:*~{~S~^, ~}~]~]"
              (thread-name thread)
              (eq :finished state)
              state
              values))))

(defun thread-alive-p (thread)
  #!+sb-doc
  "Check if THREAD is running."
  (thread-%alive-p thread))

;; A thread is eligible for gc iff it has finished and there are no
;; more references to it. This list is supposed to keep a reference to
;; all running threads.
(defvar *all-threads* ())
(defvar *all-threads-lock* (make-mutex :name "all threads lock"))

(defvar *default-alloc-signal* nil)

(defmacro with-all-threads-lock (&body body)
  `(with-system-mutex (*all-threads-lock*)
     ,@body))

(defun list-all-threads ()
  #!+sb-doc
  "Return a list of the live threads."
  (with-all-threads-lock
    (copy-list *all-threads*)))

(declaim (inline current-thread-sap))
(defun current-thread-sap ()
  (sb!vm::current-thread-offset-sap sb!vm::thread-this-slot))

(declaim (inline current-thread-os-thread))
(defun current-thread-os-thread ()
  #!+sb-thread
  (sap-int (sb!vm::current-thread-offset-sap sb!vm::thread-os-thread-slot))
  #!-sb-thread
  0)

(defun init-initial-thread ()
  (/show0 "Entering INIT-INITIAL-THREAD")
  (let ((initial-thread (%make-thread :name "initial thread"
                                      :%alive-p t
                                      :os-thread (current-thread-os-thread))))
    (setq *current-thread* initial-thread)
    ;; Either *all-threads* is empty or it contains exactly one thread
    ;; in case we are in reinit since saving core with multiple
    ;; threads doesn't work.
    (setq *all-threads* (list initial-thread))))
\f

;;;; Aliens, low level stuff

(define-alien-routine "kill_safely"
    integer
  (os-thread #!-alpha unsigned-long #!+alpha unsigned-int)
  (signal int))

#!+sb-thread
(progn
  ;; FIXME it would be good to define what a thread id is or isn't
  ;; (our current assumption is that it's a fixnum).  It so happens
  ;; that on Linux it's a pid, but it might not be on posix thread
  ;; implementations.
  (define-alien-routine ("create_thread" %create-thread)
      unsigned-long (lisp-fun-address unsigned-long))

  (define-alien-routine "block_deferrable_signals"
      void)

  #!+sb-lutex
  (progn
    (declaim (inline %lutex-init %lutex-wait %lutex-wake
                     %lutex-lock %lutex-unlock))

    (define-alien-routine ("lutex_init" %lutex-init)
        int (lutex unsigned-long))

    (define-alien-routine ("lutex_wait" %lutex-wait)
        int (queue-lutex unsigned-long) (mutex-lutex unsigned-long))

    (define-alien-routine ("lutex_wake" %lutex-wake)
        int (lutex unsigned-long) (n int))

    (define-alien-routine ("lutex_lock" %lutex-lock)
        int (lutex unsigned-long))

    (define-alien-routine ("lutex_trylock" %lutex-trylock)
        int (lutex unsigned-long))

    (define-alien-routine ("lutex_unlock" %lutex-unlock)
        int (lutex unsigned-long))

    (define-alien-routine ("lutex_destroy" %lutex-destroy)
        int (lutex unsigned-long))

    ;; FIXME: Defining a whole bunch of alien-type machinery just for
    ;; passing primitive lutex objects directly to foreign functions
    ;; doesn't seem like fun right now. So instead we just manually
    ;; pin the lutex, get its address, and let the callee untag it.
    (defmacro with-lutex-address ((name lutex) &body body)
      `(let ((,name ,lutex))
         (with-pinned-objects (,name)
           (let ((,name (get-lisp-obj-address ,name)))
             ,@body))))

    (defun make-lutex ()
      (/show0 "Entering MAKE-LUTEX")
      ;; Suppress GC until the lutex has been properly registered with
      ;; the GC.
      (without-gcing
        (let ((lutex (sb!vm::%make-lutex)))
          (/show0 "LUTEX=..")
          (/hexstr lutex)
          (with-lutex-address (lutex lutex)
            (%lutex-init lutex))
          lutex))))

  #!-sb-lutex
  (progn
    (declaim (inline futex-wait %futex-wait futex-wake))

    (define-alien-routine ("futex_wait" %futex-wait)
        int (word unsigned-long) (old-value unsigned-long)
        (to-sec long) (to-usec unsigned-long))

    (defun futex-wait (word old to-sec to-usec)
      (with-interrupts
        (%futex-wait word old to-sec to-usec)))

    (define-alien-routine "futex_wake"
        int (word unsigned-long) (n unsigned-long))))

;;; used by debug-int.lisp to access interrupt contexts
#!-(or sb-fluid sb-thread) (declaim (inline sb!vm::current-thread-offset-sap))
#!-sb-thread
(defun sb!vm::current-thread-offset-sap (n)
  (declare (type (unsigned-byte 27) n))
  (sap-ref-sap (alien-sap (extern-alien "all_threads" (* t)))
               (* n sb!vm:n-word-bytes)))

#!+sb-thread
(defun sb!vm::current-thread-offset-sap (n)
  (declare (type (unsigned-byte 27) n))
  (sb!vm::current-thread-offset-sap n))
\f

;;;; Spinlocks

(declaim (inline get-spinlock release-spinlock))

;;; Should always be called with interrupts disabled.
(defun get-spinlock (spinlock)
  (declare (optimize (speed 3) (safety 0)))
  (let* ((new *current-thread*)
         (old (sb!ext:compare-and-swap (spinlock-value spinlock) nil new)))
    (when old
      (when (eq old new)
        (error "Recursive lock attempt on ~S." spinlock))
      #!+sb-thread
      (flet ((cas ()
               (if (sb!ext:compare-and-swap (spinlock-value spinlock) nil new)
                   (thread-yield)
                   (return-from get-spinlock t))))
        (if (and (not *interrupts-enabled*) *allow-with-interrupts*)
            ;; If interrupts are disabled, but we are allowed to
            ;; enabled them, check for pending interrupts every once
            ;; in a while. %CHECK-INTERRUPTS is taking shortcuts, make
            ;; sure that deferrables are unblocked by doing an empty
            ;; WITH-INTERRUPTS once.
            (progn
              (with-interrupts)
              (loop
               (loop repeat 128 do (cas)) ; 128 is arbitrary here
               (sb!unix::%check-interrupts)))
            (loop (cas)))))
    t))

(defun release-spinlock (spinlock)
  (declare (optimize (speed 3) (safety 0)))
  ;; On x86 and x86-64 we can get away with no memory barriers, (see
  ;; Linux kernel mailing list "spin_unlock optimization(i386)"
  ;; thread, summary at
  ;; http://kt.iserv.nl/kernel-traffic/kt19991220_47.html#1.
  ;;
  ;; If the compiler may reorder this with other instructions, insert
  ;; compiler barrier here.
  ;;
  ;; FIXME: this does not work on SMP Pentium Pro and OOSTORE systems,
  ;; neither on most non-x86 architectures (but we don't have threads
  ;; on those).
  (setf (spinlock-value spinlock) nil))
\f

;;;; Mutexes

#!+sb-doc
(setf (fdocumentation 'make-mutex 'function)
      "Create a mutex."
      (fdocumentation 'mutex-name 'function)
      "The name of the mutex. Setfable.")

#!+(and sb-thread (not sb-lutex))
(progn
  (define-structure-slot-addressor mutex-state-address
      :structure mutex
      :slot state)
  ;; Important: current code assumes these are fixnums or other
  ;; lisp objects that don't need pinning.
  (defconstant +lock-free+ 0)
  (defconstant +lock-taken+ 1)
  (defconstant +lock-contested+ 2))

(defun mutex-owner (mutex)
  "Current owner of the mutex, NIL if the mutex is free. Naturally,
this is racy by design (another thread may acquire the mutex after
this function returns), it is intended for informative purposes. For
testing whether the current thread is holding a mutex see
HOLDING-MUTEX-P."
  ;; Make sure to get the current value.
  (sb!ext:compare-and-swap (mutex-%owner mutex) nil nil))

(defun get-mutex (mutex &optional (new-owner *current-thread*) (waitp t))
  #!+sb-doc
  "Acquire MUTEX for NEW-OWNER, which must be a thread or NIL. If
NEW-OWNER is NIL, it defaults to the current thread. If WAITP is
non-NIL and the mutex is in use, sleep until it is available.

Note: using GET-MUTEX to assign a MUTEX to another thread then the
current one is not recommended, and liable to be deprecated.

GET-MUTEX is not interrupt safe. The correct way to call it is:

 (WITHOUT-INTERRUPTS
   ...
   (ALLOW-WITH-INTERRUPTS (GET-MUTEX ...))
   ...)

WITHOUT-INTERRUPTS is necessary to avoid an interrupt unwinding the
call while the mutex is in an inconsistent state while
ALLOW-WITH-INTERRUPTS allows the call to be interrupted from sleep.

It is recommended that you use WITH-MUTEX instead of calling GET-MUTEX
directly."
  (declare (type mutex mutex) (optimize (speed 3))
           #!-sb-thread (ignore waitp))
  (unless new-owner
    (setq new-owner *current-thread*))
  (let ((old (mutex-%owner mutex)))
    (when (eq new-owner old)
      (error "Recursive lock attempt ~S." mutex))
    #!-sb-thread
    (when old
      (error "Strange deadlock on ~S in an unithreaded build?" mutex)))
  #!-sb-thread
  (setf (mutex-%owner mutex) new-owner)
  #!+sb-thread
  (progn
    ;; FIXME: Lutexes do not currently support deadlines, as at least
    ;; on Darwin pthread_foo_timedbar functions are not supported:
    ;; this means that we probably need to use the Carbon multiprocessing
    ;; functions on Darwin.
    ;;
    ;; FIXME: This is definitely not interrupt safe: what happens if
    ;; we get hit (1) during the lutex calls (ok, they may be safe,
    ;; but has that been checked?) (2) after the lutex call, but
    ;; before setting the mutex owner.
    #!+sb-lutex
    (when (zerop (with-lutex-address (lutex (mutex-lutex mutex))
                   (if waitp
                       (with-interrupts (%lutex-lock lutex))
                       (%lutex-trylock lutex))))
      (setf (mutex-%owner mutex) new-owner)
      t)
    #!-sb-lutex
    ;; This is a direct translation of the Mutex 2 algorithm from
    ;; "Futexes are Tricky" by Ulrich Drepper.
    (let ((old (sb!ext:compare-and-swap (mutex-state mutex)
                                        +lock-free+
                                        +lock-taken+)))
      (unless (or (eql +lock-free+ old) (not waitp))
        (tagbody
         :retry
           (when (or (eql +lock-contested+ old)
                     (not (eql +lock-free+
                               (sb!ext:compare-and-swap (mutex-state mutex)
                                                        +lock-taken+
                                                        +lock-contested+))))
             ;; Wait on the contested lock.
             (loop
              (multiple-value-bind (to-sec to-usec) (decode-timeout nil)
                (case (with-pinned-objects (mutex)
                        (futex-wait (mutex-state-address mutex)
                                    (get-lisp-obj-address +lock-contested+)
                                    (or to-sec -1)
                                    (or to-usec 0)))
                  ((1) (signal-deadline))
                  ((2))
                  (otherwise (return))))))
           (setf old (sb!ext:compare-and-swap (mutex-state mutex)
                                              +lock-free+
                                              +lock-contested+))
           ;; Did we get it?
           (unless (eql +lock-free+ old)
             (go :retry))))
      (cond ((eql +lock-free+ old)
             (let ((prev (sb!ext:compare-and-swap (mutex-%owner mutex)
                                                  nil new-owner)))
               (when prev
                 (bug "Old owner in free mutex: ~S" prev))
               t))
            (waitp
             (bug "Failed to acquire lock with WAITP."))))))

(defun release-mutex (mutex &key (if-not-owner :punt))
  #!+sb-doc
  "Release MUTEX by setting it to NIL. Wake up threads waiting for
this mutex.

RELEASE-MUTEX is not interrupt safe: interrupts should be disabled
around calls to it.

If the current thread is not the owner of the mutex then it silently
returns without doing anything (if IF-NOT-OWNER is :PUNT), signals a
WARNING (if IF-NOT-OWNER is :WARN), or releases the mutex anyway (if
IF-NOT-OWNER is :FORCE)."
  (declare (type mutex mutex))
  ;; Order matters: set owner to NIL before releasing state.
  (let* ((self *current-thread*)
         (old-owner (sb!ext:compare-and-swap (mutex-%owner mutex) self nil)))
    (unless (eql self old-owner)
      (ecase if-not-owner
        ((:punt) (return-from release-mutex nil))
        ((:warn)
         (warn "Releasing ~S, owned by another thread: ~S" mutex old-owner))
        ((:force))))
    #!+sb-thread
    (when old-owner
      (setf (mutex-%owner mutex) nil)
      #!+sb-lutex
      (with-lutex-address (lutex (mutex-lutex mutex))
        (%lutex-unlock lutex))
      #!-sb-lutex
      ;; FIXME: once ATOMIC-INCF supports struct slots with word sized
      ;; unsigned-byte type this can be used:
      ;;
      ;;     (let ((old (sb!ext:atomic-incf (mutex-state mutex) -1)))
      ;;       (unless (eql old +lock-free+)
      ;;         (setf (mutex-state mutex) +lock-free+)
      ;;         (with-pinned-objects (mutex)
      ;;           (futex-wake (mutex-state-address mutex) 1))))
      (let ((old (sb!ext:compare-and-swap (mutex-state mutex)
                                          +lock-taken+ +lock-free+)))
        (when (eql old +lock-contested+)
          (sb!ext:compare-and-swap (mutex-state mutex)
                                   +lock-contested+ +lock-free+)
          (with-pinned-objects (mutex)
            (futex-wake (mutex-state-address mutex) 1))))
      nil)))
\f

;;;; Waitqueues/condition variables

(defstruct (waitqueue (:constructor %make-waitqueue))
  #!+sb-doc
  "Waitqueue type."
  (name nil :type (or null simple-string))
  #!+(and sb-lutex sb-thread)
  (lutex (make-lutex))
  #!-sb-lutex
  (data nil))

(defun make-waitqueue (&key name)
  #!+sb-doc
  "Create a waitqueue."
  (%make-waitqueue :name name))

#!+sb-doc
(setf (fdocumentation 'waitqueue-name 'function)
      "The name of the waitqueue. Setfable.")

#!+(and sb-thread (not sb-lutex))
(define-structure-slot-addressor waitqueue-data-address
    :structure waitqueue
    :slot data)

(defun condition-wait (queue mutex)
  #!+sb-doc
  "Atomically release MUTEX and enqueue ourselves on QUEUE.  Another
thread may subsequently notify us using CONDITION-NOTIFY, at which
time we reacquire MUTEX and return to the caller."
  #!-sb-thread (declare (ignore queue))
  (assert mutex)
  #!-sb-thread (error "Not supported in unithread builds.")
  #!+sb-thread
  (let ((me *current-thread*))
    (assert (eq me (mutex-%owner mutex)))
    (/show0 "CONDITION-WAITing")
    #!+sb-lutex
    ;; Need to disable interrupts so that we don't miss setting the
    ;; owner on our way out. (pthread_cond_wait handles the actual
    ;; re-acquisition.)
    (without-interrupts
      (unwind-protect
           (progn
             (setf (mutex-%owner mutex) nil)
             (with-lutex-address (queue-lutex-address (waitqueue-lutex queue))
               (with-lutex-address (mutex-lutex-address (mutex-lutex mutex))
                 (with-local-interrupts
                   (%lutex-wait queue-lutex-address mutex-lutex-address)))))
        (setf (mutex-%owner mutex) me)))
    #!-sb-lutex
    ;; Need to disable interrupts so that we don't miss grabbing the
    ;; mutex on our way out.
    (without-interrupts
      (let ((me nil))
        ;; This setf becomes visible to other CPUS due to the usual
        ;; memory barrier semantics of lock acquire/release. This must
        ;; not be moved into the loop else wakeups may be lost upon
        ;; continuing after a deadline or EINTR.
        (setf (waitqueue-data queue) me)
        (loop
         (multiple-value-bind (to-sec to-usec) (decode-timeout nil)
           (case (unwind-protect
                      (with-pinned-objects (queue me)
                        ;; RELEASE-MUTEX is purposefully as close to
                        ;; FUTEX-WAIT as possible to reduce the size
                        ;; of the window where WAITQUEUE-DATA may be
                        ;; set by a notifier.
                        (release-mutex mutex)
                        ;; Now we go to sleep using futex-wait. If
                        ;; anyone else manages to grab MUTEX and call
                        ;; CONDITION-NOTIFY during this comment, it
                        ;; will change queue->data, and so futex-wait
                        ;; returns immediately instead of sleeping.
                        ;; Ergo, no lost wakeup. We may get spurious
                        ;; wakeups, but that's ok.
                        (allow-with-interrupts
                          (futex-wait (waitqueue-data-address queue)
                                      (get-lisp-obj-address me)
                                      ;; our way if saying "no
                                      ;; timeout":
                                      (or to-sec -1)
                                      (or to-usec 0))))
                   ;; If we are interrupted while waiting, we should
                   ;; do these things before returning. Ideally, in
                   ;; the case of an unhandled signal, we should do
                   ;; them before entering the debugger, but this is
                   ;; better than nothing.
                   (allow-with-interrupts (get-mutex mutex)))
             ;; ETIMEDOUT
             ((1) (signal-deadline))
             ;; EINTR
             ((2))
             ;; EWOULDBLOCK, -1 here, is the possible spurious wakeup
             ;; case. 0 is the normal wakeup.
             (otherwise (return)))))))))

(defun condition-notify (queue &optional (n 1))
  #!+sb-doc
  "Notify N threads waiting on QUEUE. The same mutex that is used in
the corresponding CONDITION-WAIT must be held by this thread during
this call."
  #!-sb-thread (declare (ignore queue n))
  #!-sb-thread (error "Not supported in unithread builds.")
  #!+sb-thread
  (declare (type (and fixnum (integer 1)) n))
  (/show0 "Entering CONDITION-NOTIFY")
  #!+sb-thread
  (progn
    #!+sb-lutex
    (with-lutex-address (lutex (waitqueue-lutex queue))
      (%lutex-wake lutex n))
    ;; no problem if >1 thread notifies during the comment in
    ;; condition-wait: as long as the value in queue-data isn't the
    ;; waiting thread's id, it matters not what it is
    ;; XXX we should do something to ensure that the result of this setf
    ;; is visible to all CPUs
    #!-sb-lutex
    (let ((me *current-thread*))
      (progn
        (setf (waitqueue-data queue) me)
        (with-pinned-objects (queue)
          (futex-wake (waitqueue-data-address queue) n))))))

(defun condition-broadcast (queue)
  #!+sb-doc
  "Notify all threads waiting on QUEUE."
  (condition-notify queue
                    ;; On a 64-bit platform truncating M-P-F to an int
                    ;; results in -1, which wakes up only one thread.
                    (ldb (byte 29 0)
                         most-positive-fixnum)))
\f

;;;; Semaphores

(defstruct (semaphore (:constructor %make-semaphore (name %count)))
  #!+sb-doc
  "Semaphore type. The fact that a SEMAPHORE is a STRUCTURE-OBJECT
should be considered an implementation detail, and may change in the
future."
  (name nil :type (or null simple-string))
  (%count 0 :type (integer 0))
  (waitcount 0 :type (integer 0))
  (mutex (make-mutex))
  (queue (make-waitqueue)))

(setf (fdocumentation 'semaphore-name 'function)
      "The name of the semaphore INSTANCE. Setfable.")

(declaim (inline semaphore-count))
(defun semaphore-count (instance)
  "Returns the current count of the semaphore INSTANCE."
  (semaphore-%count instance))

(defun make-semaphore (&key name (count 0))
  #!+sb-doc
  "Create a semaphore with the supplied COUNT and NAME."
  (%make-semaphore name count))

(defun wait-on-semaphore (semaphore)
  #!+sb-doc
  "Decrement the count of SEMAPHORE if the count would not be
negative. Else blocks until the semaphore can be decremented."
  ;; A more direct implementation based directly on futexes should be
  ;; possible.
  ;;
  ;; We need to disable interrupts so that we don't forget to
  ;; decrement the waitcount (which would happen if an asynch
  ;; interrupt should catch us on our way out from the loop.)
  (with-system-mutex ((semaphore-mutex semaphore) :allow-with-interrupts t)
    ;; Quick check: is it positive? If not, enter the wait loop.
    (let ((count (semaphore-%count semaphore)))
      (if (plusp count)
          (setf (semaphore-%count semaphore) (1- count))
          (unwind-protect
               (progn
                 (incf (semaphore-waitcount semaphore))
                 (loop until (plusp (setf count (semaphore-%count semaphore)))
                       do (condition-wait (semaphore-queue semaphore)
                                          (semaphore-mutex semaphore)))
                 (setf (semaphore-%count semaphore) (1- count)))
            (decf (semaphore-waitcount semaphore)))))))

(defun signal-semaphore (semaphore &optional (n 1))
  #!+sb-doc
  "Increment the count of SEMAPHORE by N. If there are threads waiting
on this semaphore, then N of them is woken up."
  (declare (type (integer 1) n))
  ;; Need to disable interrupts so that we don't lose a wakeup after
  ;; we have incremented the count.
  (with-system-mutex ((semaphore-mutex semaphore))
    (let ((waitcount (semaphore-waitcount semaphore))
          (count (incf (semaphore-%count semaphore) n)))
      (when (plusp waitcount)
        (condition-notify (semaphore-queue semaphore) (min waitcount count))))))
\f

;;;; Job control, independent listeners

(defstruct session
  (lock (make-mutex :name "session lock"))
  (threads nil)
  (interactive-threads nil)
  (interactive-threads-queue (make-waitqueue)))

(defvar *session* nil)

;;; The debugger itself tries to acquire the session lock, don't let
;;; funny situations (like getting a sigint while holding the session
;;; lock) occur. At the same time we need to allow interrupts while
;;; *waiting* for the session lock for things like GET-FOREGROUND to
;;; be interruptible.
;;;
;;; Take care: we sometimes need to obtain the session lock while
;;; holding on to *ALL-THREADS-LOCK*, so we must _never_ obtain it
;;; _after_ getting a session lock! (Deadlock risk.)
;;;
;;; FIXME: It would be good to have ordered locks to ensure invariants
;;; like the above.
(defmacro with-session-lock ((session) &body body)
  `(with-system-mutex ((session-lock ,session) :allow-with-interrupts t)
     ,@body))

(defun new-session ()
  (make-session :threads (list *current-thread*)
                :interactive-threads (list *current-thread*)))

(defun init-job-control ()
  (/show0 "Entering INIT-JOB-CONTROL")
  (setf *session* (new-session))
  (/show0 "Exiting INIT-JOB-CONTROL"))

(defun %delete-thread-from-session (thread session)
  (with-session-lock (session)
    (setf (session-threads session)
          (delete thread (session-threads session))
          (session-interactive-threads session)
          (delete thread (session-interactive-threads session)))))

(defun call-with-new-session (fn)
  (%delete-thread-from-session *current-thread* *session*)
  (let ((*session* (new-session)))
    (funcall fn)))

(defmacro with-new-session (args &body forms)
  (declare (ignore args))               ;for extensibility
  (sb!int:with-unique-names (fb-name)
    `(labels ((,fb-name () ,@forms))
      (call-with-new-session (function ,fb-name)))))

;;; Remove thread from its session, if it has one.
#!+sb-thread
(defun handle-thread-exit (thread)
  (/show0 "HANDLING THREAD EXIT")
  ;; Lisp-side cleanup
  (with-all-threads-lock
    (setf (thread-%alive-p thread) nil)
    (setf (thread-os-thread thread) nil)
    (setq *all-threads* (delete thread *all-threads*))
    (when *session*
      (%delete-thread-from-session thread *session*)))
  #!+sb-lutex
  (without-gcing
    (/show0 "FREEING MUTEX LUTEX")
    (with-lutex-address (lutex (mutex-lutex (thread-interruptions-lock thread)))
      (%lutex-destroy lutex))))

(defun terminate-session ()
  #!+sb-doc
  "Kill all threads in session except for this one.  Does nothing if current
thread is not the foreground thread."
  ;; FIXME: threads created in other threads may escape termination
  (let ((to-kill
         (with-session-lock (*session*)
           (and (eq *current-thread*
                    (car (session-interactive-threads *session*)))
                (session-threads *session*)))))
    ;; do the kill after dropping the mutex; unwind forms in dying
    ;; threads may want to do session things
    (dolist (thread to-kill)
      (unless (eq thread *current-thread*)
        ;; terminate the thread but don't be surprised if it has
        ;; exited in the meantime
        (handler-case (terminate-thread thread)
          (interrupt-thread-error ()))))))

;;; called from top of invoke-debugger
(defun debugger-wait-until-foreground-thread (stream)
  "Returns T if thread had been running in background, NIL if it was
interactive."
  (declare (ignore stream))
  #!-sb-thread nil
  #!+sb-thread
  (prog1
      (with-session-lock (*session*)
        (not (member *current-thread*
                     (session-interactive-threads *session*))))
    (get-foreground)))

(defun get-foreground ()
  #!-sb-thread t
  #!+sb-thread
  (let ((was-foreground t))
    (loop
     (/show0 "Looping in GET-FOREGROUND")
     (with-session-lock (*session*)
       (let ((int-t (session-interactive-threads *session*)))
         (when (eq (car int-t) *current-thread*)
           (unless was-foreground
             (format *query-io* "Resuming thread ~A~%" *current-thread*))
           (return-from get-foreground t))
         (setf was-foreground nil)
         (unless (member *current-thread* int-t)
           (setf (cdr (last int-t))
                 (list *current-thread*)))
         (condition-wait
          (session-interactive-threads-queue *session*)
          (session-lock *session*)))))))

(defun release-foreground (&optional next)
  #!+sb-doc
  "Background this thread.  If NEXT is supplied, arrange for it to
have the foreground next."
  #!-sb-thread (declare (ignore next))
  #!-sb-thread nil
  #!+sb-thread
  (with-session-lock (*session*)
    (when (rest (session-interactive-threads *session*))
      (setf (session-interactive-threads *session*)
            (delete *current-thread* (session-interactive-threads *session*))))
    (when next
      (setf (session-interactive-threads *session*)
            (list* next
                   (delete next (session-interactive-threads *session*)))))
    (condition-broadcast (session-interactive-threads-queue *session*))))

(defun foreground-thread ()
  (car (session-interactive-threads *session*)))

(defun make-listener-thread (tty-name)
  (assert (probe-file tty-name))
  (let* ((in (sb!unix:unix-open (namestring tty-name) sb!unix:o_rdwr #o666))
         (out (sb!unix:unix-dup in))
         (err (sb!unix:unix-dup in)))
    (labels ((thread-repl ()
               (sb!unix::unix-setsid)
               (let* ((sb!impl::*stdin*
                       (make-fd-stream in :input t :buffering :line
                                       :dual-channel-p t))
                      (sb!impl::*stdout*
                       (make-fd-stream out :output t :buffering :line
                                              :dual-channel-p t))
                      (sb!impl::*stderr*
                       (make-fd-stream err :output t :buffering :line
                                              :dual-channel-p t))
                      (sb!impl::*tty*
                       (make-fd-stream err :input t :output t
                                              :buffering :line
                                              :dual-channel-p t))
                      (sb!impl::*descriptor-handlers* nil))
                 (with-new-session ()
                   (unwind-protect
                        (sb!impl::toplevel-repl nil)
                     (sb!int:flush-standard-output-streams))))))
      (make-thread #'thread-repl))))
\f

;;;; The beef

(defun make-thread (function &key name)
  #!+sb-doc
  "Create a new thread of NAME that runs FUNCTION. When the function
returns the thread exits. The return values of FUNCTION are kept
around and can be retrieved by JOIN-THREAD."
  #!-sb-thread (declare (ignore function name))
  #!-sb-thread (error "Not supported in unithread builds.")
  #!+sb-thread
  (let* ((thread (%make-thread :name name))
         (setup-sem (make-semaphore :name "Thread setup semaphore"))
         (real-function (coerce function 'function))
         (initial-function
          (lambda ()
            ;; In time we'll move some of the binding presently done in C
            ;; here too.
            ;;
            ;; KLUDGE: Here we have a magic list of variables that are
            ;; not thread-safe for one reason or another.  As people
            ;; report problems with the thread safety of certain
            ;; variables, (e.g. "*print-case* in multiple threads
            ;; broken", sbcl-devel 2006-07-14), we add a few more
            ;; bindings here.  The Right Thing is probably some variant
            ;; of Allegro's *cl-default-special-bindings*, as that is at
            ;; least accessible to users to secure their own libraries.
            ;;   --njf, 2006-07-15
            ;;
            ;; As it is, this lambda must not cons until we are ready
            ;; to run GC. Be very careful.
            (let* ((*current-thread* thread)
                   (*restart-clusters* nil)
                   (*handler-clusters* (sb!kernel::initial-handler-clusters))
                   (*condition-restarts* nil)
                   (sb!impl::*deadline* nil)
                   (sb!impl::*step-out* nil)
                   ;; internal printer variables
                   (sb!impl::*previous-case* nil)
                   (sb!impl::*previous-readtable-case* nil)
                   (empty (vector))
                   (sb!impl::*merge-sort-temp-vector* empty)
                   (sb!impl::*zap-array-data-temp* empty)
                   (sb!impl::*internal-symbol-output-fun* nil)
                   (sb!impl::*descriptor-handlers* nil)) ; serve-event
              ;; Binding from C
              (setf sb!vm:*alloc-signal* *default-alloc-signal*)
              (setf (thread-os-thread thread) (current-thread-os-thread))
              (with-mutex ((thread-result-lock thread))
                (with-all-threads-lock
                  (push thread *all-threads*))
                (with-session-lock (*session*)
                  (push thread (session-threads *session*)))
                (setf (thread-%alive-p thread) t)
                (signal-semaphore setup-sem)
                ;; can't use handling-end-of-the-world, because that flushes
                ;; output streams, and we don't necessarily have any (or we
                ;; could be sharing them)
                (catch 'sb!impl::toplevel-catcher
                  (catch 'sb!impl::%end-of-the-world
                    (with-simple-restart
                        (terminate-thread
                         (format nil
                                 "~~@<Terminate this thread (~A)~~@:>"
                                 *current-thread*))
                      (without-interrupts
                        (unwind-protect
                             (with-local-interrupts
                               ;; Now that most things have a chance
                               ;; to work properly without messing up
                               ;; other threads, it's time to enable
                               ;; signals.
                               (sb!unix::unblock-deferrable-signals)
                               (setf (thread-result thread)
                                     (cons t
                                           (multiple-value-list
                                            (funcall real-function))))
                               ;; Try to block deferrables. An
                               ;; interrupt may unwind it, but for a
                               ;; normal exit it prevents interrupt
                               ;; loss.
                               (block-deferrable-signals))
                          ;; We're going down, can't handle interrupts
                          ;; sanely anymore. GC remains enabled.
                          (block-deferrable-signals)
                          ;; We don't want to run interrupts in a dead
                          ;; thread when we leave WITHOUT-INTERRUPTS.
                          ;; This potentially causes important
                          ;; interupts to be lost: SIGINT comes to
                          ;; mind.
                          (setq *interrupt-pending* nil)
                          (handle-thread-exit thread))))))))
            (values))))
    ;; If the starting thread is stopped for gc before it signals the
    ;; semaphore then we'd be stuck.
    (assert (not *gc-inhibit*))
    ;; Keep INITIAL-FUNCTION pinned until the child thread is
    ;; initialized properly. Wrap the whole thing in
    ;; WITHOUT-INTERRUPTS because we pass INITIAL-FUNCTION to another
    ;; thread.
    (without-interrupts
      (with-pinned-objects (initial-function)
        (let ((os-thread
               (%create-thread
                (get-lisp-obj-address initial-function))))
          (when (zerop os-thread)
            (error "Can't create a new thread"))
          (wait-on-semaphore setup-sem)
          thread)))))

(define-condition join-thread-error (error)
  ((thread :reader join-thread-error-thread :initarg :thread))
  #!+sb-doc
  (:documentation "Joining thread failed.")
  (:report (lambda (c s)
             (format s "Joining thread failed: thread ~A ~
                        has not returned normally."
                     (join-thread-error-thread c)))))

#!+sb-doc
(setf (fdocumentation 'join-thread-error-thread 'function)
      "The thread that we failed to join.")

(defun join-thread (thread &key (default nil defaultp))
  #!+sb-doc
  "Suspend current thread until THREAD exits. Returns the result
values of the thread function. If the thread does not exit normally,
return DEFAULT if given or else signal JOIN-THREAD-ERROR."
  (with-system-mutex ((thread-result-lock thread) :allow-with-interrupts t)
    (cond ((car (thread-result thread))
           (return-from join-thread
             (values-list (cdr (thread-result thread)))))
          (defaultp
           (return-from join-thread default))))
  (error 'join-thread-error :thread thread))

(defun destroy-thread (thread)
  #!+sb-doc
  "Deprecated. Same as TERMINATE-THREAD."
  (terminate-thread thread))

(define-condition interrupt-thread-error (error)
  ((thread :reader interrupt-thread-error-thread :initarg :thread))
  #!+sb-doc
  (:documentation "Interrupting thread failed.")
  (:report (lambda (c s)
             (format s "Interrupt thread failed: thread ~A has exited."
                     (interrupt-thread-error-thread c)))))

#!+sb-doc
(setf (fdocumentation 'interrupt-thread-error-thread 'function)
      "The thread that was not interrupted.")

(defmacro with-interruptions-lock ((thread) &body body)
  `(with-system-mutex ((thread-interruptions-lock ,thread))
     ,@body))

;;; Called from the signal handler.
#!-win32
(defun run-interruption ()
  (let ((interruption (with-interruptions-lock (*current-thread*)
                        (pop (thread-interruptions *current-thread*)))))
    ;; If there is more to do, then resignal and let the normal
    ;; interrupt deferral mechanism take care of the rest. From the
    ;; OS's point of view the signal we are in the handler for is no
    ;; longer pending, so the signal will not be lost.
    (when (thread-interruptions *current-thread*)
      (kill-safely (thread-os-thread *current-thread*) sb!unix:sigpipe))
    (when interruption
      (funcall interruption))))

(defun interrupt-thread (thread function)
  #!+sb-doc
  "Interrupt the live THREAD and make it run FUNCTION. A moderate
degree of care is expected for use of INTERRUPT-THREAD, due to its
nature: if you interrupt a thread that was holding important locks
then do something that turns out to need those locks, you probably
won't like the effect. FUNCTION runs with interrupts disabled, but
WITH-INTERRUPTS is allowed in it. Keep in mind that many things may
enable interrupts (GET-MUTEX when contended, for instance) so the
first thing to do is usually a WITH-INTERRUPTS or a
WITHOUT-INTERRUPTS. Within a thread interrupts are queued, they are
run in same the order they were sent."
  #!+win32
  (declare (ignore thread))
  #!+win32
  (with-interrupt-bindings
    (with-interrupts (funcall function)))
  #!-win32
  (let ((os-thread (thread-os-thread thread)))
    (cond ((not os-thread)
           (error 'interrupt-thread-error :thread thread))
          (t
           (with-interruptions-lock (thread)
             ;; Append to the end of the interruptions queue. It's
             ;; O(N), but it does not hurt to slow interruptors down a
             ;; bit when the queue gets long.
             (setf (thread-interruptions thread)
                   (append (thread-interruptions thread)
                           (list (lambda ()
                                   (without-interrupts
                                     (allow-with-interrupts
                                       (funcall function))))))))
           (when (minusp (kill-safely os-thread sb!unix:sigpipe))
             (error 'interrupt-thread-error :thread thread))))))

(defun terminate-thread (thread)
  #!+sb-doc
  "Terminate the thread identified by THREAD, by causing it to run
SB-EXT:QUIT - the usual cleanup forms will be evaluated"
  (interrupt-thread thread 'sb!ext:quit))

(define-alien-routine "thread_yield" int)

#!+sb-doc
(setf (fdocumentation 'thread-yield 'function)
      "Yield the processor to other threads.")

;;; internal use only.  If you think you need to use these, either you
;;; are an SBCL developer, are doing something that you should discuss
;;; with an SBCL developer first, or are doing something that you
;;; should probably discuss with a professional psychiatrist first
#!+sb-thread
(progn
  (defun %thread-sap (thread)
    (let ((thread-sap (alien-sap (extern-alien "all_threads" (* t))))
          (target (thread-os-thread thread)))
      (loop
        (when (sap= thread-sap (int-sap 0)) (return nil))
        (let ((os-thread (sap-ref-word thread-sap
                                       (* sb!vm:n-word-bytes
                                          sb!vm::thread-os-thread-slot))))
          (when (= os-thread target) (return thread-sap))
          (setf thread-sap
                (sap-ref-sap thread-sap (* sb!vm:n-word-bytes
                                           sb!vm::thread-next-slot)))))))

  (defun %symbol-value-in-thread (symbol thread)
    (tagbody
       ;; Prevent the dead from dying completely while we look for the
       ;; TLS area...
       (with-all-threads-lock
         (if (thread-alive-p thread)
             (let* ((offset (* sb!vm:n-word-bytes
                               (sb!vm::symbol-tls-index symbol)))
                    (tl-val (sap-ref-word (%thread-sap thread) offset)))
               (if (eql tl-val sb!vm::no-tls-value-marker-widetag)
                   (go :unbound)
                   (return-from %symbol-value-in-thread
                     (values (make-lisp-obj tl-val) t))))
             (return-from %symbol-value-in-thread (values nil nil))))
     :unbound
       (error "Cannot read thread-local symbol value: ~S unbound in ~S"
              symbol thread)))

  (defun %set-symbol-value-in-thread (symbol thread value)
    (tagbody
       (with-pinned-objects (value)
         ;; Prevent the dead from dying completely while we look for
         ;; the TLS area...
         (with-all-threads-lock
           (if (thread-alive-p thread)
               (let* ((offset (* sb!vm:n-word-bytes
                                 (sb!vm::symbol-tls-index symbol)))
                      (sap (%thread-sap thread))
                      (tl-val (sap-ref-word sap offset)))
                 (if (eql tl-val sb!vm::no-tls-value-marker-widetag)
                     (go :unbound)
                     (setf (sap-ref-word sap offset)
                           (get-lisp-obj-address value)))
                 (return-from %set-symbol-value-in-thread (values value t)))
               (return-from %set-symbol-value-in-thread (values nil nil)))))
     :unbound
       (error "Cannot set thread-local symbol value: ~S unbound in ~S"
              symbol thread))))

(defun sb!vm::locked-symbol-global-value-add (symbol-name delta)
  (sb!vm::locked-symbol-global-value-add symbol-name delta))
\f

;;;; Stepping

(defun thread-stepping ()
  (make-lisp-obj
   (sap-ref-word (current-thread-sap)
                 (* sb!vm::thread-stepping-slot sb!vm:n-word-bytes))))

(defun (setf thread-stepping) (value)
  (setf (sap-ref-word (current-thread-sap)
                      (* sb!vm::thread-stepping-slot sb!vm:n-word-bytes))
        (get-lisp-obj-address value)))