Use *NSYNC for POSIX threads locking APIs

Condition variables, barriers, and r/w locks now work very well.
2025-05-30 01:02:29 +00:00 · 2022-09-11 11:02:07 -07:00 · 2022-09-11 11:02:07 -07:00 · b5cb71ab84
commit b5cb71ab84
parent 3de35e196c
197 changed files with 3734 additions and 3817 deletions
--- a/third_party/nsync/futex.c
+++ b/third_party/nsync/futex.c
@ -0,0 +1,124 @@
+/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8   -*-│
+│vi: set et ft=c ts=8 tw=8 fenc=utf-8                                       :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ 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.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/strace.internal.h"
+#include "libc/calls/struct/timespec.internal.h"
+#include "libc/dce.h"
+#include "libc/errno.h"
+#include "libc/intrin/describeflags.internal.h"
+#include "libc/sysv/consts/futex.h"
+#include "libc/thread/thread.h"
+#include "third_party/nsync/common.internal.h"
+#include "third_party/nsync/futex.internal.h"
+// clang-format off
+
+/* futex() polyfill w/ sched_yield() fallback */
+
+#define FUTEX_WAIT_BITS_ FUTEX_BITSET_MATCH_ANY
+
+int _futex (int *, int, int, const struct timespec *, int *, int);
+
+static int FUTEX_WAIT_;
+static int FUTEX_WAKE_;
+static int FUTEX_PRIVATE_FLAG_;
+static bool FUTEX_IS_SUPPORTED;
+bool FUTEX_TIMEOUT_IS_ABSOLUTE;
+
+__attribute__((__constructor__)) static void sync_futex_init_ (void) {
+	int x = 0;
+
+	FUTEX_WAKE_ = FUTEX_WAKE;
+
+	if (IsLinux () && 
+	    _futex (&x, FUTEX_WAIT_BITSET, 1, 0, 0,
+		    FUTEX_BITSET_MATCH_ANY) == -EAGAIN) {
+		FUTEX_WAIT_ = FUTEX_WAIT_BITSET;
+		FUTEX_TIMEOUT_IS_ABSOLUTE = true;
+	} else {
+		FUTEX_WAIT_ = FUTEX_WAIT;
+	}
+
+	if (IsOpenbsd () ||
+	    (IsLinux () && 
+	     !_futex (&x, FUTEX_WAKE_PRIVATE, 1, 0, 0, 0))) {
+		FUTEX_PRIVATE_FLAG_ = FUTEX_PRIVATE_FLAG;
+	}
+
+	// In our testing, we found that the monotonic clock on various
+	// popular systems (such as Linux, and some BSD variants) was no
+	// better behaved than the realtime clock, and routinely took
+	// large steps backwards, especially on multiprocessors. Given
+	// that "monotonic" doesn't seem to mean what it says,
+	// implementers of nsync_time might consider retaining the
+	// simplicity of a single epoch within an address space, by
+	// configuring any time synchronization mechanism (like ntp) to
+	// adjust for leap seconds by adjusting the rate, rather than
+	// with a backwards step.
+	if (IsLinux () &&
+	    _futex (&x, FUTEX_WAIT_BITSET | FUTEX_CLOCK_REALTIME,
+		    1, 0, 0, FUTEX_BITSET_MATCH_ANY) == -EAGAIN) {
+		FUTEX_WAIT_ |= FUTEX_CLOCK_REALTIME;
+	}
+
+        FUTEX_IS_SUPPORTED = IsLinux() || IsOpenbsd();
+}
+
+int nsync_futex_wait_ (int *p, int expect, char pshare, struct timespec *timeout) {
+	int rc, op;
+	if (FUTEX_IS_SUPPORTED) {
+		op = FUTEX_WAIT_;
+		if (pshare == PTHREAD_PROCESS_PRIVATE) {
+			op |= FUTEX_PRIVATE_FLAG_;
+		}
+		rc = _futex (p, op, expect, timeout, 0, FUTEX_WAIT_BITS_);
+		if (IsOpenbsd() && rc > 0) {
+			// [jart] openbsd does this without setting carry flag
+			rc = -rc;
+		}
+		STRACE("futex(%t, %s, %d, %s) → %s",
+		       p, DescribeFutexOp(op), expect,
+		       DescribeTimespec(0, timeout), DescribeFutexResult(rc));
+	} else {
+		nsync_yield_ ();
+		if (timeout) {
+			rc = -ETIMEDOUT;
+		} else {
+			rc = 0;
+		}
+	}
+	return rc;
+}
+
+int nsync_futex_wake_ (int *p, int count, char pshare) {
+	int rc, op;
+	int wake (void *, int, int) asm ("_futex");
+	if (FUTEX_IS_SUPPORTED) {
+		op = FUTEX_WAKE_;
+		if (pshare == PTHREAD_PROCESS_PRIVATE) {
+			op |= FUTEX_PRIVATE_FLAG_;
+		}
+		rc = wake (p, op, count);
+		STRACE("futex(%t, %s, %d) → %s", p,
+		       DescribeFutexOp(op),
+		       count, DescribeFutexResult(rc));
+	} else {
+		nsync_yield_ ();
+		rc = 0;
+	}
+	return rc;
+}