QMutex/Unix: remove the pthread_mutex_t-based content

For our purposes, the sem_t code is better, so we've preferred it since
commit c7ab816af110ea08809e1aabd8bf1e08967c6d53 (5.7). Olivier wrote in
that commit's message, "It makes tst_QMutex::contendedQMutex with no
msleep 8 times faster".

That's true because QMutex didn't lock the underlying pthread_mutex_t in
QMutex::lock(), as we used the inlined atomic code for the uncontended
case.

It is probably possible to merge the qmutex_mac.cpp and qmutex_unix.cpp
code now (both are based on semaphores), but I won't do that for two
reasons:
 1) At best, the PThread functions are going to be thin-wrappers around
    the code we already have, like FreeBSD's are around usem (see [1])
 2) Darwin has a private API that resembles futexes so we may want to
    go that way eventually (see [2])

[1] https://github.com/freebsd/freebsd-src/blob/main/lib/libc/gen/sem_new.c
[2] https://codereview.qt-project.org/335849

Change-Id: Idd5e1bb52be047d7b4fffffd175369b13ba47bed
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/thread/qmutex_p.h

@@ -28,10 +28,7 @@
 #if defined(Q_OS_DARWIN)
 # include <mach/semaphore.h>
 #elif defined(Q_OS_UNIX)
-# if _POSIX_VERSION-0 >= 200112L || _XOPEN_VERSION-0 >= 600
 #  include <semaphore.h>
-#  define QT_UNIX_SEMAPHORE
-# endif
 #endif
 
 struct timespec;
@@ -87,23 +84,11 @@ public:
     //platform specific stuff
 #if defined(Q_OS_DARWIN)
     semaphore_t mach_semaphore;
-#elif defined(QT_UNIX_SEMAPHORE)
-    sem_t semaphore;
 #elif defined(Q_OS_UNIX)
-    bool wakeup;
-    pthread_mutex_t mutex;
-    pthread_cond_t cond;
+    sem_t semaphore;
 #endif
 };
 
-
-#ifdef Q_OS_UNIX
-// helper functions for qmutex_unix.cpp and qwaitcondition_unix.cpp
-// they are in qwaitcondition_unix.cpp actually
-void qt_initialize_pthread_cond(pthread_cond_t *cond, const char *where);
-void qt_abstime_for_timeout(struct timespec *ts, QDeadlineTimer deadline);
-#endif
-
 QT_END_NAMESPACE
 
 #endif // QMUTEX_P_H

src/corelib/thread/qmutex_unix.cpp

@@ -25,8 +25,6 @@ static void report_error(int code, const char *where, const char *what)
         qErrnoWarning(code, "%s: %s failure", where, what);
 }
 
-#ifdef QT_UNIX_SEMAPHORE
-
 QMutexPrivate::QMutexPrivate()
 {
     report_error(sem_init(&semaphore, 0, 0), "QMutex", "sem_init");
@@ -68,56 +66,4 @@ void QMutexPrivate::wakeUp() noexcept
     report_error(sem_post(&semaphore), "QMutex::unlock", "sem_post");
 }
 
-#else // QT_UNIX_SEMAPHORE
-
-QMutexPrivate::QMutexPrivate()
-    : wakeup(false)
-{
-    report_error(pthread_mutex_init(&mutex, NULL), "QMutex", "mutex init");
-    qt_initialize_pthread_cond(&cond, "QMutex");
-}
-
-QMutexPrivate::~QMutexPrivate()
-{
-    report_error(pthread_cond_destroy(&cond), "QMutex", "cv destroy");
-    report_error(pthread_mutex_destroy(&mutex), "QMutex", "mutex destroy");
-}
-
-bool QMutexPrivate::wait(int timeout)
-{
-    report_error(pthread_mutex_lock(&mutex), "QMutex::lock", "mutex lock");
-    int errorCode = 0;
-    while (!wakeup) {
-        if (timeout < 0) {
-            errorCode = pthread_cond_wait(&cond, &mutex);
-        } else {
-            timespec ti;
-            qt_abstime_for_timeout(&ti, QDeadlineTimer(timeout));
-            errorCode = pthread_cond_timedwait(&cond, &mutex, &ti);
-        }
-        if (errorCode) {
-            if (errorCode == ETIMEDOUT) {
-                if (wakeup)
-                    errorCode = 0;
-                break;
-            }
-            report_error(errorCode, "QMutex::lock()", "cv wait");
-        }
-    }
-    bool ret = wakeup;
-    wakeup = false;
-    report_error(pthread_mutex_unlock(&mutex), "QMutex::lock", "mutex unlock");
-    return ret;
-}
-
-void QMutexPrivate::wakeUp() noexcept
-{
-    report_error(pthread_mutex_lock(&mutex), "QMutex::unlock", "mutex lock");
-    wakeup = true;
-    report_error(pthread_cond_signal(&cond), "QMutex::unlock", "cv signal");
-    report_error(pthread_mutex_unlock(&mutex), "QMutex::unlock", "mutex unlock");
-}
-
-#endif
-
 QT_END_NAMESPACE

src/corelib/thread/qwaitcondition_unix.cpp

@@ -52,7 +52,7 @@ static void report_error(int code, const char *where, const char *what)
         qErrnoWarning(code, "%s: %s failure", where, what);
 }
 
-void qt_initialize_pthread_cond(pthread_cond_t *cond, const char *where)
+static void qt_initialize_pthread_cond(pthread_cond_t *cond, const char *where)
 {
     pthread_condattr_t *attrp = nullptr;
 
@@ -69,7 +69,7 @@ void qt_initialize_pthread_cond(pthread_cond_t *cond, const char *where)
     report_error(pthread_cond_init(cond, attrp), where, "cv init");
 }
 
-void qt_abstime_for_timeout(timespec *ts, QDeadlineTimer deadline)
+static void qt_abstime_for_timeout(timespec *ts, QDeadlineTimer deadline)
 {
     using namespace std::chrono;
     using Clock =