impl-lispworks-condition-variables.lisp - clic - Clic is an command line interactive client for gopher written in Common LISP (HTM) git clone git://bitreich.org/clic/ git://enlrupgkhuxnvlhsf6lc3fziv5h2hhfrinws65d7roiv6bfj7d652fid.onion/clic/ (DIR) Log (DIR) Files (DIR) Refs (DIR) Tags (DIR) README (DIR) LICENSE --- impl-lispworks-condition-variables.lisp (7140B) --- 1 ;;;; -*- indent-tabs-mode: nil -*- 2 3 (in-package #:bordeaux-threads) 4 5 ;; Lispworks condition support is simulated, albeit via a lightweight wrapper over 6 ;; its own polling-based wait primitive. Waiters register with the condition variable, 7 ;; and use MP:process-wait which queries for permission to proceed at its own (usspecified) interval. 8 ;; http://www.lispworks.com/documentation/lw51/LWRM/html/lwref-445.htm 9 ;; A wakeup callback (on notify) is provided to lighten this query to not have to do a hash lookup 10 ;; on every poll (or have to serialize on the condition variable) and a mechanism is put 11 ;; in place to unregister any waiter that exits wait for other reasons, 12 ;; and to resend any (single) notification that may have been consumed before this (corner 13 ;; case). Much of the complexity present is to support single notification (as recommended in 14 ;; the spec); but a distinct condition-notify-all is provided for reference. 15 ;; Single-notification follows a first-in first-out ordering 16 ;; 17 ;; Performance: With 1000 threads waiting on one condition-variable, the steady-state hit (at least 18 ;; as tested on a 3GHz Win32 box) is noise - hovering at 0% on Task manager. 19 ;; While not true zero like a true native solution, the use of the Lispworks native checks appear 20 ;; fast enough to be an equivalent substitute (thread count will cause issue before the 21 ;; waiting overhead becomes significant) 22 (defstruct (condition-variable (:constructor make-lw-condition (name))) 23 name 24 (lock (mp:make-lock :name "For condition-variable") :type mp:lock :read-only t) 25 (wait-tlist (cons nil nil) :type cons :read-only t) 26 (wait-hash (make-hash-table :test 'eq) :type hash-table :read-only t) 27 ;; unconsumed-notifications is to track :remove-from-consideration 28 ;; for entries that may have exited prematurely - notification is sent through 29 ;; to someone else, and offender is removed from hash and list 30 (unconsumed-notifications (make-hash-table :test 'eq) :type hash-table :read-only t)) 31 32 (defun make-condition-variable (&key name) 33 (make-lw-condition name)) 34 35 (defmacro with-cv-access (condition-variable &body body) 36 (let ((cv-sym (gensym)) 37 (slots '(lock wait-tlist wait-hash unconsumed-notifications))) 38 `(let ((,cv-sym ,condition-variable)) 39 (with-slots ,slots 40 ,cv-sym 41 (macrolet ((locked (&body body) `(mp:with-lock (lock) ,@body))) 42 (labels ((,(gensym) () ,@slots))) ; Trigger expansion of the symbol-macrolets to ignore 43 ,@body))))) 44 45 (defmacro defcvfun (function-name (condition-variable &rest args) &body body) 46 `(defun ,function-name (,condition-variable ,@args) 47 (with-cv-access ,condition-variable 48 ,@body))) 49 #+lispworks (editor:setup-indent "defcvfun" 2 2 7) ; indent defcvfun 50 51 ; utility function thath assumes process is locked on condition-variable's lock. 52 (defcvfun do-notify-single (condition-variable) ; assumes already locked 53 (let ((id (caar wait-tlist))) 54 (when id 55 (pop (car wait-tlist)) 56 (unless (car wait-tlist) ; check for empty 57 (setf (cdr wait-tlist) nil)) 58 (funcall (gethash id wait-hash)) ; call waiter-wakeup 59 (remhash id wait-hash) ; absence of entry = permission to proceed 60 (setf (gethash id unconsumed-notifications) t)))) 61 62 ;; Added for completeness/to show how it's done in this paradigm; but 63 ;; The symbol for this call is not exposed in the api 64 (defcvfun condition-notify-all (condition-variable) 65 (locked 66 (loop for waiter-wakeup being the hash-values in wait-hash do (funcall waiter-wakeup)) 67 (clrhash wait-hash) 68 (clrhash unconsumed-notifications) ; don't care as everyone just got notified 69 (setf (car wait-tlist) nil) 70 (setf (cdr wait-tlist) nil))) 71 72 ;; Currently implemented so as to notify only one waiting thread 73 (defcvfun condition-notify (condition-variable) 74 (locked (do-notify-single condition-variable))) 75 76 (defun delete-from-tlist (tlist element) 77 (let ((deleter 78 (lambda () 79 (setf (car tlist) (cdar tlist)) 80 (unless (car tlist) 81 (setf (cdr tlist) nil))))) 82 (loop for cons in (car tlist) do 83 (if (eq element (car cons)) 84 (progn 85 (funcall deleter) 86 (return nil)) 87 (let ((cons cons)) 88 (setq deleter 89 (lambda () 90 (setf (cdr cons) (cddr cons)) 91 (unless (cdr cons) 92 (setf (cdr tlist) cons))))))))) 93 94 (defun add-to-tlist-tail (tlist element) 95 (let ((new-link (cons element nil))) 96 (cond 97 ((car tlist) 98 (setf (cddr tlist) new-link) 99 (setf (cdr tlist) new-link)) 100 (t 101 (setf (car tlist) new-link) 102 (setf (cdr tlist) new-link))))) 103 104 (defcvfun condition-wait (condition-variable lock- &key timeout) 105 (signal-error-if-condition-wait-timeout timeout) 106 (mp:process-unlock lock-) 107 (unwind-protect ; for the re-taking of the lock. Guarding all of the code 108 (let ((wakeup-allowed-to-proceed nil) 109 (wakeup-lock (mp:make-lock :name "wakeup lock for condition-wait"))) 110 ;; wakeup-allowed-to-proceed is an optimisation to avoid having to serialize all waiters and 111 ;; search the hashtable. That it is locked is for safety/completeness, although 112 ;; as wakeup-allowed-to-proceed only transitions nil -> t, and that missing it once or twice is 113 ;; moot in this situation, it would be redundant even if ever a Lispworks implementation ever became 114 ;; non-atomic in its assigments 115 (let ((id (cons nil nil)) 116 (clean-exit nil)) 117 (locked 118 (add-to-tlist-tail wait-tlist id) 119 (setf (gethash id wait-hash) (lambda () (mp:with-lock (wakeup-lock) (setq wakeup-allowed-to-proceed t))))) 120 (unwind-protect 121 (progn 122 (mp:process-wait 123 "Waiting for notification" 124 (lambda () 125 (when (mp:with-lock (wakeup-lock) wakeup-allowed-to-proceed) 126 (locked (not (gethash id wait-hash)))))) 127 (locked (remhash id unconsumed-notifications)) 128 (setq clean-exit t)) ; Notification was consumed 129 ;; Have to call remove-from-consideration just in case process was interrupted 130 ;; rather than having condition met 131 (unless clean-exit ; clean-exit is just an optimization 132 (locked 133 (when (gethash id wait-hash) ; not notified - must have been interrupted 134 ;; Have to unsubscribe 135 (remhash id wait-hash) 136 (delete-from-tlist wait-tlist id)) 137 ;; note - it's possible to be removed from wait-hash/wait-tlist (in notify-single); but still have an unconsumed notification! 138 (when (gethash id unconsumed-notifications) ; Must have exited for reasons unrelated to notification 139 (remhash id unconsumed-notifications) ; Have to pass on the notification to an eligible waiter 140 (do-notify-single condition-variable))))))) 141 (mp:process-lock lock-)) 142 t) 143 144 (define-condition-wait-compiler-macro)