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85f64f3851
Thanks to @autumnjolitz (in #876) the Cosmopolitan codebase is now acquainted with Apple's outstanding ulock system calls which offer something much closer to futexes than Grand Central Dispatch which wasn't quite as good, since its wait function can't be interrupted by signals (therefore necessitating a busy loop) and it also needs semaphore objects to be created and freed. Even though ulock is an internal Apple API, strictly speaking, the benefits of futexes are so great that it's worth the risk for now especially since we have the GCD implementation still as a quick escape hatch if it changes Here's why this change is important for x86 XNU users. Cosmo has a suboptimal polyfill when the operating system doesn't offer an API that let's us implement futexes properly. Sadly we had to use that on X86 XNU until now. The polyfill works using clock_nanosleep, to poll the futex in a busy loop with exponential backoff. On XNU x86 clock_nanosleep suffers from us not being able to use a fast clock gettime implementation, which had a compounding effect that's made the polyfill function even more poorly. On X86 XNU we also need to polyfill sched_yield() using select(), which made things even more troublesome. Now that we have futexes we don't have any busy loops anymore for both condition variables and thread joining so optimal performance is attained. To demonstrate, consider these benchmarks Before: $ ./lockscale_test.com -b consumed 38.8377 seconds real time and 0.087131 seconds cpu time After: $ ./lockscale_test.com -b consumed 0.007955 seconds real time and 0.011515 seconds cpu time Fixes #876
113 lines
4.3 KiB
C
113 lines
4.3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2023 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/calls/calls.h"
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#include "libc/calls/struct/sigaction.h"
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#include "libc/calls/struct/siginfo.h"
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#include "libc/calls/struct/sigset.h"
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#include "libc/calls/ucontext.h"
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#include "libc/dce.h"
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#include "libc/runtime/runtime.h"
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#include "libc/runtime/sysconf.h"
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#include "libc/sysv/consts/auxv.h"
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#include "libc/sysv/consts/map.h"
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#include "libc/sysv/consts/o.h"
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#include "libc/sysv/consts/prot.h"
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#include "libc/sysv/consts/sa.h"
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#include "libc/sysv/consts/sicode.h"
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#include "libc/sysv/consts/sig.h"
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#include "libc/testlib/testlib.h"
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#include "third_party/xed/x86.h"
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volatile int gotsig;
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volatile int gotcode;
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void SetUpOnce(void) {
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testlib_enable_tmp_setup_teardown();
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}
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void SetUp(void) {
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gotsig = 0;
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}
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void OnSig(int sig, siginfo_t *si, void *arg) {
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ucontext_t *ctx = arg;
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gotsig = sig;
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gotcode = si->si_code;
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#ifdef __aarch64__
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ctx->uc_mcontext.pc += 4;
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#elif defined(__x86_64__)
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struct XedDecodedInst xedd;
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xed_decoded_inst_zero_set_mode(&xedd, XED_MACHINE_MODE_LONG_64);
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xed_instruction_length_decode(&xedd, (void *)ctx->uc_mcontext.rip, 15);
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ctx->uc_mcontext.rip += xedd.length;
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#else
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#error "unsupported architecture"
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#endif /* __x86_64__ */
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}
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TEST(sigbus, test) {
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if (IsWindows()) {
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// TODO(jart): Just write a kernel style memory manager from scratch
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// for WIN32 and don't depend on their mapping functions
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return;
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}
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// create a file with less than one page of content
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ASSERT_SYS(0, 3, open("foo", O_CREAT | O_RDWR, 0666));
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ASSERT_SYS(0, 2, write(3, "hi", 2));
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// map two pages of the file into memory
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char *map;
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long pagesz = getauxval(AT_PAGESZ);
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ASSERT_NE(MAP_FAILED,
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(map = mmap(0, pagesz * 2, PROT_READ, MAP_PRIVATE, 3, 0)));
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// verify the file content is there
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ASSERT_EQ('h', map[0]);
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ASSERT_EQ('i', map[1]);
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// memory reads past file eof on first page get zero-filled
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ASSERT_EQ(0, map[2]);
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// listen for sigbus
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struct sigaction sa;
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struct sigaction oldsa;
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sa.sa_flags = SA_SIGINFO;
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sa.sa_sigaction = OnSig;
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sigemptyset(&sa.sa_mask);
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sigaction(SIGBUS, &sa, &oldsa);
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// memory reads past file eof on subsequent pages cause page fault to sigbus
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volatile char x = map[pagesz];
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(void)x;
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// verify the signal was raised
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EXPECT_EQ(SIGBUS, gotsig);
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if (IsXnuSilicon()) {
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// TODO: Why does it say it's an alignment error?
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EXPECT_EQ(BUS_ADRALN, gotcode);
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} else {
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EXPECT_EQ(BUS_ADRERR, gotcode);
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}
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// clean up
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sigaction(SIGBUS, &oldsa, 0);
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munmap(map, pagesz * 2);
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}
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