src/code/barrier.lisp

   1 ;;;; Support for memory barriers required for multithreaded operation
   2
   3 ;;;; This software is part of the SBCL system. See the README file for
   4 ;;;; more information.
   5 ;;;;
   6 ;;;; This software is derived from the CMU CL system, which was
   7 ;;;; written at Carnegie Mellon University and released into the
   8 ;;;; public domain. The software is in the public domain and is
   9 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
  10 ;;;; files for more information.
  11
  12 (in-package "SB!THREAD")
  13
  14
  15 ;;;; Interpreter stubs for the various barrier functions
  16
  17 #!-memory-barrier-vops
  18 (declaim (inline sb!vm:%compiler-barrier sb!vm:%memory-barrier
  19                  sb!vm:%read-barrier sb!vm:%write-barrier
  20                  sb!vm:%data-dependency-barrier))
  21 (defun sb!vm:%compiler-barrier ()
  22   #!+memory-barrier-vops (sb!vm:%compiler-barrier)
  23   (values))
  24 (defun sb!vm:%memory-barrier ()
  25   #!+memory-barrier-vops (sb!vm:%memory-barrier)
  26   (values))
  27 (defun sb!vm:%read-barrier ()
  28   #!+memory-barrier-vops (sb!vm:%read-barrier)
  29   (values))
  30 (defun sb!vm:%write-barrier ()
  31   #!+memory-barrier-vops (sb!vm:%write-barrier)
  32   (values))
  33 (defun sb!vm:%data-dependency-barrier ()
  34   #!+memory-barrier-vops (sb!vm:%data-dependency-barrier)
  35   (values))
  36
  37
  38 ;;;; The actual barrier macro and support
  39 (defmacro barrier ((kind) &body forms)
  40   "Insert a barrier in the code stream, preventing some sort of
  41 reordering.
  42
  43 KIND should be one of:
  44
  45   :COMPILER
  46     Prevent the compiler from reordering memory access across the
  47     barrier.
  48   :MEMORY
  49     Prevent the cpu from reordering any memory access across the
  50     barrier.
  51   :READ
  52     Prevent the cpu from reordering any read access across the
  53     barrier.
  54   :WRITE
  55     Prevent the cpu from reordering any write access across the
  56     barrier.
  57   :DATA-DEPENDENCY
  58     Prevent the cpu from reordering dependent memory reads across the
  59     barrier (requiring reads before the barrier to complete before any
  60     reads after the barrier that depend on them).  This is a weaker
  61     form of the :READ barrier.
  62
  63 FORMS is an implicit PROGN, evaluated before the barrier.  BARRIER
  64 returns the values of the last form in FORMS.
  65
  66 The file \"memory-barriers.txt\" in the Linux kernel documentation is
  67 highly recommended reading for anyone programming at this level."
  68   `(multiple-value-prog1
  69     (progn ,@forms)
  70     (,(or (getf '(:compiler        sb!vm:%compiler-barrier
  71                   :memory          sb!vm:%memory-barrier
  72                   :read            sb!vm:%read-barrier
  73                   :write           sb!vm:%write-barrier
  74                   :data-dependency sb!vm:%data-dependency-barrier)
  75                 kind)
  76           (error "Unknown barrier kind ~S" kind)))))