Add shared memory apis to redbean

You can now do things like implement mutexes using futexes in your
redbean lua code. This provides the fastest possible inter-process
communication for your production systems when SQLite alone as ipc
or things like pipes aren't sufficient.

test/tool/net/mapshared_test.lua

@@ -0,0 +1,85 @@
+-- Copyright 2022 Justine Alexandra Roberts Tunney
+--
+-- Permission to use, copy, modify, and/or distribute this software for
+-- any purpose with or without fee is hereby granted, provided that the
+-- above copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+-- WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+-- WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+-- AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+-- DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+-- PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+-- TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+assert(unix.pledge("stdio proc"))
+
+words = 2
+processes = 8
+iterations = 10000
+
+mem = unix.mapshared(words * 8)
+
+--------------------------------------------------------------------------------
+-- test shared memory string reading and writing
+
+mem:write('hello')
+assert(mem:read() == 'hello')
+mem:write('hi')
+assert(mem:read() == 'hi')
+assert(mem:read(0, 5) == 'hi\0lo')
+mem:write('H', 0, 1)
+assert(mem:read(0, 5) == 'Hi\0lo')
+assert(mem:read(1, 1) == 'i')
+
+--------------------------------------------------------------------------------
+-- test shared memory locking primitives
+
+mem:store(0, 0)
+assert(mem:xchg(0, 1) == 0)
+assert(mem:xchg(0, 2) == 1)
+
+mem:store(0, 0)
+ok, old = mem:cmpxchg(0, 0, 1)
+assert(ok and old == 0)
+ok, old = mem:cmpxchg(0, 666, 777)
+assert(not ok and old == 1)
+assert(mem:add(0, 3) == 1)
+assert(mem:load(0) == 4)
+
+--------------------------------------------------------------------------------
+-- test atomic addition across concurrent processes
+
+function Worker()
+    for i = 1,iterations do
+        mem:add(0, 1)
+    end
+end
+
+mem:store(0, 0)
+for i = 1,processes do
+    pid = assert(unix.fork())
+    if pid == 0 then
+        Worker()
+        unix.exit(0)
+    end
+end
+while true do
+    rc, ws = unix.wait(0)
+    if not rc then
+        assert(ws:errno() == unix.ECHILD)
+        break
+    end
+    if unix.WIFEXITED(ws) then
+        if unix.WEXITSTATUS(ws) ~= 0 then
+            print('process %d exited with %s' % {rc, unix.WEXITSTATUS(ws)})
+            unix.exit(1)
+        end
+    else
+        print('process %d terminated with %s' % {rc, unix.WTERMSIG(ws)})
+        unix.exit(1)
+    end
+end
+
+assert(mem:load(0) == processes * iterations)