"1.0.41.2": threads: Add memory-barrier framework.

* New file, src/code/barrier.lisp, containing the baseline
implementation.

  * Added the barrier functions to the compiler function database.

  * Export the interface macro, BARRIER, from SB!THREAD and the
underlying barrier functions from SB!VM.

  * Document a new architecture-dependent build-time feature,
MEMORY-BARRIER-VOPS, for controlling the behavior and inlining of
the interpreter stubs for the barrier functions.

base-target-features.lisp-expr

@@ -390,6 +390,10 @@
  ;;   :compare-and-swap-vops
  ;;     The backend implements compare-and-swap VOPs.
  ;;
+ ;;   :memory-barrier-vops
+ ;;     Memory barriers (for multi-threaded synchronization) have been
+ ;;     implemented for this platform.
+ ;;
  ;; operating system features:
  ;;   :unix    = We're intended to run under some Unix-like OS. (This is not
  ;;              exclusive with the features which indicate which particular

build-order.lisp-expr

@@ -467,6 +467,9 @@
  ;; This has ASSEMBLY-UNIT-related stuff needed by core.lisp.
  ("src/compiler/early-assem")
 
+ ;; This has the BARRIER stuff that the threading support needs.
+ ("src/code/barrier")
+
  ;; core.lisp contains DEFSTRUCT CORE-OBJECT, and "compiler/main.lisp"
  ;; does lots of (TYPEP FOO 'CORE-OBJECT), so it's nice to compile this
  ;; before "compiler/main.lisp" so that those can be coded efficiently

package-data-list.lisp-expr

@@ -1928,6 +1928,8 @@ is a good idea, but see SB-SYS re. blurring of boundaries."
                "THREAD-ALIVE-P"
                "THREAD-NAME"
                "THREAD-YIELD"
+               ;; Memory barrier
+               "BARRIER"
                ;; Mutexes
                "GET-MUTEX"
                "GRAB-MUTEX"
@@ -2470,6 +2472,8 @@ structure representations"
                "*PRIMITIVE-OBJECTS*"
                "+HIGHEST-NORMAL-GENERATION+"
                "+PSEUDO-STATIC-GENERATION+"
+               "%COMPILER-BARRIER" "%DATA-DEPENDENCY-BARRIER"
+               "%MEMORY-BARRIER" "%READ-BARRIER" "%WRITE-BARRIER"
                "AFTER-BREAKPOINT-TRAP"
                "ANY-REG-SC-NUMBER" "ARRAY-DATA-SLOT" "ARRAY-DIMENSIONS-OFFSET"
                "ARRAY-DISPLACED-P-SLOT" "ARRAY-DISPLACEMENT-SLOT"

src/code/barrier.lisp

@@ -0,0 +1,79 @@
+;;;; Support for memory barriers required for multithreaded operation
+
+;;;; 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")
+
+
+;;;; Interpreter stubs for the various barrier functions
+
+#!-memory-barrier-vops
+(declaim (inline sb!vm:%compiler-barrier sb!vm:%memory-barrier
+                 sb!vm:%read-barrier sb!vm:%write-barrier
+                 sb!vm:%data-dependency-barrier))
+(defun sb!vm:%compiler-barrier ()
+  #!+memory-barrier-vops (sb!vm:%compiler-barrier)
+  (values))
+(defun sb!vm:%memory-barrier ()
+  #!+memory-barrier-vops (sb!vm:%memory-barrier)
+  (values))
+(defun sb!vm:%read-barrier ()
+  #!+memory-barrier-vops (sb!vm:%read-barrier)
+  (values))
+(defun sb!vm:%write-barrier ()
+  #!+memory-barrier-vops (sb!vm:%write-barrier)
+  (values))
+(defun sb!vm:%data-dependency-barrier ()
+  #!+memory-barrier-vops (sb!vm:%data-dependency-barrier)
+  (values))
+
+
+;;;; The actual barrier macro and support
+(defparameter *barrier-kind-functions*
+  '(:compiler sb!vm:%compiler-barrier :memory sb!vm:%memory-barrier
+    :read sb!vm:%read-barrier :write sb!vm:%write-barrier
+    :data-dependency sb!vm:%data-dependency-barrier))
+
+(defun barrier-kind-function (kind)
+  (or (getf *barrier-kind-functions* kind)
+      (error "Unknown barrier kind ~S" kind)))
+
+(defmacro barrier ((kind) &body forms)
+    "Insert a barrier in the code stream, preventing some sort of
+reordering.
+
+KIND should be one of:
+
+  :COMPILER
+    Prevent the compiler from reordering memory access across the
+    barrier.
+  :MEMORY
+    Prevent the cpu from reordering any memory access across the
+    barrier.
+  :READ
+    Prevent the cpu from reordering any read access across the
+    barrier.
+  :WRITE
+    Prevent the cpu from reordering any write access across the
+    barrier.
+  :DATA-DEPENDENCY
+    Prevent the cpu from reordering dependent memory reads across the
+    barrier (requiring reads before the barrier to complete before any
+    reads after the barrier that depend on them).  This is a weaker
+    form of the :READ barrier.
+
+FORMS is an implicit PROGN, evaluated before the barrier.  BARRIER
+returns the values of the last form in FORMS.
+
+The file \"memory-barriers.txt\" in the Linux kernel documentation is
+highly recommended reading for anyone programming at this level."
+  `(multiple-value-prog1
+    (progn ,@forms)
+    (,(barrier-kind-function kind))))

src/compiler/fndb.lisp

@@ -1577,6 +1577,16 @@
   ())
 (defknown style-warn (t &rest t) null ())
 
+
+;;;; memory barriers
+
+(defknown sb!vm:%compiler-barrier () (values) ())
+(defknown sb!vm:%memory-barrier () (values) ())
+(defknown sb!vm:%read-barrier () (values) ())
+(defknown sb!vm:%write-barrier () (values) ())
+(defknown sb!vm:%data-dependency-barrier () (values) ())
+
+
 ;;;; atomic ops
 (defknown %compare-and-swap-svref (simple-vector index t t) t
     (unsafe))

version.lisp-expr

@@ -17,4 +17,4 @@
 ;;; checkins which aren't released. (And occasionally for internal
 ;;; versions, especially for internal versions off the main CVS
 ;;; branch, it gets hairier, e.g. "0.pre7.14.flaky4.13".)
-"1.0.41.1"
+"1.0.41.2"