;;; any system calls, and by then the cost of the extra system calls
;;; are lost in the noise when compared with the cost of delivering
;;; the signal in the first place.
+;;;
+;;; The conditional bindings done by this code here are worth the
+;;; trouble as binding is more expensive then read & test -- so
+;;; (if *foo*
+;;; (foo)
+;;; (let ((*foo* t))
+;;; (foo)))
+;;; is faster then
+;;; (let ((*foo* t))
+;;; (foo))
+;;; provided that the first branch is true "often enough".
(defvar *interrupts-enabled* t)
(defvar *interrupt-pending* nil)
+#!+sb-thruption (defvar *thruption-pending* nil)
+(defvar *allow-with-interrupts* t)
+;;; This is to support signal handlers that want to return to the
+;;; interrupted context without leaving anything extra on the stack. A
+;;; simple
+;;;
+;;; (without-interrupts
+;;; (unblock-deferrable-signals)
+;;; (allow-with-interrupts ...))
+;;;
+;;; would not cut it, as upon leaving WITHOUT-INTERRUPTS the pending
+;;; handlers is run with stuff from the function in which this is
+;;; still on the stack.
+(defvar *unblock-deferrables-on-enabling-interrupts-p* nil)
(sb!xc:defmacro without-interrupts (&body body)
#!+sb-doc
- "Execute BODY in a context impervious to interrupts."
- (let ((name (gensym "WITHOUT-INTERRUPTS-BODY-")))
- `(flet ((,name () ,@body))
+ "Executes BODY with all deferrable interrupts disabled. Deferrable
+interrupts arriving during execution of the BODY take effect after BODY has
+been executed.
+
+Deferrable interrupts include most blockable POSIX signals, and
+SB-THREAD:INTERRUPT-THREAD. Does not interfere with garbage collection, and
+unlike in many traditional Lisps using userspace threads, in SBCL
+WITHOUT-INTERRUPTS does not inhibit scheduling of other threads.
+
+Binds ALLOW-WITH-INTERRUPTS and WITH-LOCAL-INTERRUPTS as a local macros.
+
+ALLOW-WITH-INTERRUPTS allows the WITH-INTERRUPTS to take effect during the
+dynamic scope of its body, unless there is an outer WITHOUT-INTERRUPTS without
+a corresponding ALLOW-WITH-INTERRUPTS.
+
+WITH-LOCAL-INTERRUPTS executes its body with interrupts enabled provided that
+for there is an ALLOW-WITH-INTERRUPTS for every WITHOUT-INTERRUPTS surrounding
+the current one. WITH-LOCAL-INTERRUPTS is equivalent to:
+
+ (allow-with-interrupts (with-interrupts ...))
+
+Care must be taken not to let either ALLOW-WITH-INTERRUPTS or
+WITH-LOCAL-INTERRUPTS appear in a function that escapes from inside the
+WITHOUT-INTERRUPTS in:
+
+ (without-interrupts
+ ;; The body of the lambda would be executed with WITH-INTERRUPTS allowed
+ ;; regardless of the interrupt policy in effect when it is called.
+ (lambda () (allow-with-interrupts ...)))
+
+ (without-interrupts
+ ;; The body of the lambda would be executed with interrupts enabled
+ ;; regardless of the interrupt policy in effect when it is called.
+ (lambda () (with-local-interrupts ...)))
+"
+ (with-unique-names (outer-allow-with-interrupts without-interrupts-body)
+ `(dx-flet ((,without-interrupts-body ()
+ (declare (disable-package-locks allow-with-interrupts
+ with-local-interrupts))
+ (macrolet
+ ((allow-with-interrupts
+ (&body allow-forms)
+ `(let ((*allow-with-interrupts*
+ ,',outer-allow-with-interrupts))
+ ,@allow-forms))
+ (with-local-interrupts
+ (&body with-forms)
+ `(let ((*allow-with-interrupts*
+ ,',outer-allow-with-interrupts)
+ (*interrupts-enabled*
+ ,',outer-allow-with-interrupts))
+ (when ,',outer-allow-with-interrupts
+ (when *unblock-deferrables-on-enabling-interrupts-p*
+ (setq *unblock-deferrables-on-enabling-interrupts-p*
+ nil)
+ (sb!unix::unblock-deferrable-signals))
+ (when (or *interrupt-pending*
+ #!+sb-thruption *thruption-pending*)
+ (receive-pending-interrupt)))
+ (locally ,@with-forms))))
+ (let ((*interrupts-enabled* nil)
+ (,outer-allow-with-interrupts *allow-with-interrupts*)
+ (*allow-with-interrupts* nil))
+ (declare (ignorable ,outer-allow-with-interrupts))
+ (declare (enable-package-locks allow-with-interrupts
+ with-local-interrupts))
+ ,@body))))
(if *interrupts-enabled*
- (unwind-protect
- (let ((*interrupts-enabled* nil))
- (,name))
- ;; FIXME: Does it matter that an interrupt coming in here
- ;; could be executed before any of the pending interrupts?
- ;; Or do incoming interrupts have the good grace to check
- ;; whether interrupts are pending before executing themselves
- ;; immediately?
- (when *interrupt-pending*
- (receive-pending-interrupt)))
- (,name)))))
+ (unwind-protect
+ (,without-interrupts-body)
+ ;; If we were interrupted in the protected section,
+ ;; then the interrupts are still blocked and it remains
+ ;; so until the pending interrupt is handled.
+ ;;
+ ;; If we were not interrupted in the protected section,
+ ;; but here, then even if the interrupt handler enters
+ ;; another WITHOUT-INTERRUPTS, the pending interrupt will be
+ ;; handled immediately upon exit from said
+ ;; WITHOUT-INTERRUPTS, so it is as if nothing has happened.
+ (when (or *interrupt-pending*
+ #!+sb-thruption *thruption-pending*)
+ (receive-pending-interrupt)))
+ (,without-interrupts-body)))))
(sb!xc:defmacro with-interrupts (&body body)
#!+sb-doc
- "Allow interrupts while executing BODY. As interrupts are normally allowed,
- this is only useful inside a WITHOUT-INTERRUPTS."
- (let ((name (gensym)))
- `(flet ((,name () ,@body))
- (if *interrupts-enabled*
- (,name)
- (let ((*interrupts-enabled* t))
- (when *interrupt-pending*
- (receive-pending-interrupt))
- (,name))))))
+ "Executes BODY with deferrable interrupts conditionally enabled. If there
+are pending interrupts they take effect prior to executing BODY.
+
+As interrupts are normally allowed WITH-INTERRUPTS only makes sense if there
+is an outer WITHOUT-INTERRUPTS with a corresponding ALLOW-WITH-INTERRUPTS:
+interrupts are not enabled if any outer WITHOUT-INTERRUPTS is not accompanied
+by ALLOW-WITH-INTERRUPTS."
+ (with-unique-names (allowp enablep)
+ ;; We could manage without ENABLEP here, but that would require
+ ;; taking extra care not to ever have *ALLOW-WITH-INTERRUPTS* NIL
+ ;; and *INTERRUPTS-ENABLED* T -- instead of risking future breakage
+ ;; we take the tiny hit here.
+ `(let* ((,allowp *allow-with-interrupts*)
+ (,enablep *interrupts-enabled*)
+ (*interrupts-enabled* (or ,enablep ,allowp)))
+ (when (and ,allowp (not ,enablep))
+ (when *unblock-deferrables-on-enabling-interrupts-p*
+ (setq *unblock-deferrables-on-enabling-interrupts-p* nil)
+ (sb!unix::unblock-deferrable-signals))
+ (when (or *interrupt-pending*
+ #!+sb-thruption *thruption-pending*)
+ (receive-pending-interrupt)))
+ (locally ,@body))))
+
+(defmacro allow-with-interrupts (&body body)
+ (declare (ignore body))
+ (error "~S is valid only inside ~S."
+ 'allow-with-interrupts 'without-interrupts))
+
+(defmacro with-local-interrupts (&body body)
+ (declare (ignore body))
+ (error "~S is valid only inside ~S."
+ 'with-local-interrupts 'without-interrupts))
+
+;;; A low-level operation that assumes that *INTERRUPTS-ENABLED* is
+;;; false, *ALLOW-WITH-INTERRUPTS* is true and deferrable signals are
+;;; unblocked.
+(defun %check-interrupts ()
+ ;; Here we check for pending interrupts first, because reading a
+ ;; special is faster then binding it!
+ (when (or *interrupt-pending* #!+sb-thruption *thruption-pending*)
+ (let ((*interrupts-enabled* t))
+ (receive-pending-interrupt))))
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