1 ;;;; Support for memory barriers required for multithreaded operation
3 ;;;; This software is part of the SBCL system. See the README file for
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.
12 (in-package "SB!THREAD")
15 ;;;; Interpreter stubs for the various barrier functions
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
)
24 (defun sb!vm
:%memory-barrier
()
25 #!+memory-barrier-vops
(sb!vm
:%memory-barrier
)
27 (defun sb!vm
:%read-barrier
()
28 #!+memory-barrier-vops
(sb!vm
:%read-barrier
)
30 (defun sb!vm
:%write-barrier
()
31 #!+memory-barrier-vops
(sb!vm
:%write-barrier
)
33 (defun sb!vm
:%data-dependency-barrier
()
34 #!+memory-barrier-vops
(sb!vm
:%data-dependency-barrier
)
38 ;;;; The actual barrier macro and support
39 (defconstant-eqx +barrier-kind-functions
+
40 '(:compiler sb
!vm
:%compiler-barrier
:memory sb
!vm
:%memory-barrier
41 :read sb
!vm
:%read-barrier
:write sb
!vm
:%write-barrier
42 :data-dependency sb
!vm
:%data-dependency-barrier
)
45 (defmacro barrier
((kind) &body forms
)
47 "Insert a barrier in the code stream, preventing some sort of
50 KIND should be one of:
53 Prevent the compiler from reordering memory access across the
56 Prevent the cpu from reordering any memory access across the
59 Prevent the cpu from reordering any read access across the
62 Prevent the cpu from reordering any write access across the
65 Prevent the cpu from reordering dependent memory reads across the
66 barrier (requiring reads before the barrier to complete before any
67 reads after the barrier that depend on them). This is a weaker
68 form of the :READ barrier.
70 FORMS is an implicit PROGN, evaluated before the barrier. BARRIER
71 returns the values of the last form in FORMS.
73 The file \"memory-barriers.txt\" in the Linux kernel documentation is
74 highly recommended reading for anyone programming at this level."
75 `(multiple-value-prog1
77 (,(or (getf +barrier-kind-functions
+ kind
)
78 (error "Unknown barrier kind ~S" kind
)))))