Long live futexes for FreeBSD!

Like commit 91f6460aff0a6ab5142f16d5f4fc1f559ca1c325 which added support
for Windows. This API is documented and has apparently been present in
FreeBSD for a long while.

The DragonflyBSD API is very similar, but I don't have one to confirm
that I've coded correctly. OpenBSD and NetBSD may have similar APIs, but
I haven't even researched them. We're open to contributions, though.

Change-Id: I63b988479db546dabffcfffd1766bc431fed614b
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/corelib/CMakeLists.txt

@@ -690,6 +690,11 @@ qt_internal_extend_target(Core CONDITION QT_FEATURE_thread AND UNIX AND NOT APPL
         thread/qmutex_unix.cpp
 )
 
+qt_internal_extend_target(Core CONDITION QT_FEATURE_thread AND FREEBSD
+    SOURCES
+        thread/qfutex_freebsd_p.h
+)
+
 qt_internal_extend_target(Core CONDITION QT_FEATURE_thread AND LINUX
     SOURCES
         thread/qfutex_linux_p.h

src/corelib/thread/qfutex_freebsd_p.h

@@ -0,0 +1,82 @@
+// Copyright (C) 2023 Intel Corporation.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QFUTEX_FREEBSD_P_H
+#define QFUTEX_FREEBSD_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <private/qcore_unix_p.h>
+#include <qdeadlinetimer.h>
+
+// https://man.freebsd.org/cgi/man.cgi?query=_umtx_op
+#include <sys/umtx.h>
+
+#define QT_ALWAYS_USE_FUTEX
+
+QT_BEGIN_NAMESPACE
+
+namespace QtFreeBSDFutex {
+constexpr inline bool futexAvailable() { return true; }
+
+template <typename Atomic>
+inline int do_wait(Atomic &futex, typename Atomic::Type expectedValue, _umtx_time *tmp = nullptr)
+{
+    // FreeBSD UMTX_OP_WAIT does not apply acquire or release memory barriers,
+    // so there are no QtTsan calls here.
+
+    int op = UMTX_OP_WAIT_UINT_PRIVATE;
+    if (sizeof(futex) > sizeof(quint32))
+        op = UMTX_OP_WAIT;  // no _PRIVATE version
+
+    // The timeout is passed in uaddr2, with its size in uaddr
+    void *uaddr = reinterpret_cast<void *>(tmp ? sizeof(*tmp) : 0);
+    void *uaddr2 = tmp;
+    int ret = _umtx_op(&futex, op, u_long(expectedValue), uaddr, uaddr2);
+
+    return ret;
+}
+
+template <typename Atomic>
+inline void futexWait(Atomic &futex, typename Atomic::Type expectedValue)
+{
+    do_wait(futex, expectedValue);
+}
+
+template <typename Atomic>
+inline bool futexWait(Atomic &futex, typename Atomic::Type expectedValue, QDeadlineTimer timer)
+{
+    struct _umtx_time tm = {};
+    auto deadline = timer.deadline<std::chrono::steady_clock>();
+    tm._timeout = durationToTimespec(deadline.time_since_epoch());
+    tm._flags = UMTX_ABSTIME;
+    tm._clockid = CLOCK_MONOTONIC;
+    int r = do_wait(futex, expectedValue, &tm);
+    return r == 0 || errno != ETIMEDOUT;
+}
+
+template <typename Atomic> inline void futexWakeOne(Atomic &futex)
+{
+    _umtx_op(&futex, UMTX_OP_WAKE_PRIVATE, 1, nullptr, nullptr);
+}
+
+template <typename Atomic> inline void futexWakeAll(Atomic &futex)
+{
+    _umtx_op(&futex, UMTX_OP_WAKE_PRIVATE, INT_MAX, nullptr, nullptr);
+}
+} //namespace QtFreeBSDFutex
+
+namespace QtFutex = QtFreeBSDFutex;
+
+QT_END_NAMESPACE
+
+#endif // QFUTEX_FREEBSD_P_H

src/corelib/thread/qfutex_p.h

@@ -33,13 +33,14 @@ namespace QtDummyFutex {
 
 QT_END_NAMESPACE
 
-#if defined(Q_OS_LINUX) && !defined(QT_LINUXBASE)
+#if defined(Q_OS_FREEBSD)
+#  include "qfutex_freebsd_p.h"
+#elif defined(Q_OS_LINUX) && !defined(QT_LINUXBASE)
 // use Linux mutexes everywhere except for LSB builds
 #  include "qfutex_linux_p.h"
 #elif defined(Q_OS_WIN)
 #  include "qfutex_win_p.h"
 #else
-
 QT_BEGIN_NAMESPACE
 namespace QtFutex = QtDummyFutex;
 QT_END_NAMESPACE

tests/auto/corelib/thread/qmutex/tst_qmutex.cpp

@@ -145,43 +145,43 @@ void tst_QMutex::tryLock_non_recursive()
     Thread thread;
     thread.start();
 
-    // TEST 1: thread can't acquire lock
+    qDebug("TEST 1: thread can't acquire lock");
     testsTurn.acquire();
     normalMutex.lock();
     QVERIFY(lockCount.testAndSetRelaxed(0, 1));
     threadsTurn.release();
 
-    // TEST 2: thread can acquire lock
+    qDebug("TEST 2: thread can acquire lock");
     testsTurn.acquire();
     QVERIFY(lockCount.testAndSetRelaxed(1, 0));
     normalMutex.unlock();
     threadsTurn.release();
 
-    // TEST 3: thread can't acquire lock, timeout = waitTime
+    qDebug("TEST 3: thread can't acquire lock, timeout = waitTime");
     testsTurn.acquire();
     normalMutex.lock();
     QVERIFY(lockCount.testAndSetRelaxed(0, 1));
     threadsTurn.release();
 
-    // TEST 4: thread can acquire lock, timeout = waitTime
+    qDebug("TEST 4: thread can acquire lock, timeout = waitTime");
     testsTurn.acquire();
     QVERIFY(lockCount.testAndSetRelaxed(1, 0));
     normalMutex.unlock();
     threadsTurn.release();
 
-    // TEST 5: thread can't acquire lock, timeout = 0
+    qDebug("TEST 5: thread can't acquire lock, timeout = 0");
     testsTurn.acquire();
     normalMutex.lock();
     QVERIFY(lockCount.testAndSetRelaxed(0, 1));
     threadsTurn.release();
 
-    // TEST 6: thread can acquire lock, timeout = 0
+    qDebug("TEST 6: thread can acquire lock, timeout = 0");
     testsTurn.acquire();
     QVERIFY(lockCount.testAndSetRelaxed(1, 0));
     normalMutex.unlock();
     threadsTurn.release();
 
-    // TEST 7: thread can acquire lock, timeout = 3000   (QTBUG-24795)
+    qDebug("TEST 7: thread can acquire lock, timeout = 3000   (QTBUG-24795)");
     testsTurn.acquire();
     normalMutex.lock();
     threadsTurn.release();