From 999cebcb5df0269d24d65db579a7c78a94053c2e Mon Sep 17 00:00:00 2001
From: Bobby Bingham <koorogi@koorogi.info>
Date: Mon, 27 Mar 2023 22:07:16 -0500
Subject: [PATCH] Fix level when using pthreads recursive mutex

When using the pthreads recursive mutex, the level method was only able
to return either zero or one, but a recursive mutex can be locked more
than once.

Additionally, the way this detected if the mutex was already locked was
to test whether it can be locked again. If testing from the thread that
is currently holding the lock, this locking attempt always succeeds, and
therefore determines that the lock is _not_ held at all. This is
especially bad, as this operation only makes sense to perform from the
thread that holds the lock -- if any thread not holding the lock queries
the number of times the lock is held, that answer can change before the
thread can used it.

Signed-off-by: Bobby Bingham <koorogi@koorogi.info>
---
 src/tools/qmutex_unix.cpp | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/src/tools/qmutex_unix.cpp b/src/tools/qmutex_unix.cpp
index dae1533c..5cb037a1 100644
--- a/src/tools/qmutex_unix.cpp
+++ b/src/tools/qmutex_unix.cpp
@@ -88,6 +88,7 @@ public:
     int level();
 
     bool recursive;
+    int count;
 };
 
 #ifndef    Q_RECURSIVE_MUTEX_TYPE
@@ -127,7 +128,7 @@ TQMutexPrivate::~TQMutexPrivate()
 
 // real mutex class
 TQRealMutexPrivate::TQRealMutexPrivate(bool recurs)
-    : recursive(recurs)
+    : count(0), recursive(recurs)
 {
     pthread_mutexattr_t attr;
     pthread_mutexattr_init(&attr);
@@ -146,36 +147,31 @@ void TQRealMutexPrivate::lock()
 {
     int ret = pthread_mutex_lock(&handle);
 
+    if (!ret) {
+	count++;
+    } else {
 #ifdef QT_CHECK_RANGE
-    if (ret)
 	tqWarning("Mutex lock failure: %s", strerror(ret));
 #endif
+    }
 }
 
 void TQRealMutexPrivate::unlock()
 {
+    count--;
     int ret = pthread_mutex_unlock(&handle);
 
+    if (ret) {
+	count++;
 #ifdef QT_CHECK_RANGE
-    if (ret)
 	tqWarning("Mutex unlock failure: %s", strerror(ret));
 #endif
+    }
 }
 
 bool TQRealMutexPrivate::locked()
 {
-    int ret = pthread_mutex_trylock(&handle);
-
-    if (ret == EBUSY) {
-	return TRUE;
-    } else if (ret) {
-#ifdef QT_CHECK_RANGE
-	tqWarning("Mutex locktest failure: %s", strerror(ret));
-#endif
-    } else
-	pthread_mutex_unlock(&handle);
-
-    return FALSE;
+    return count > 0;
 }
 
 bool TQRealMutexPrivate::trylock()
@@ -201,7 +197,7 @@ int TQRealMutexPrivate::type() const
 
 int TQRealMutexPrivate::level()
 {
-    return locked();
+    return count;
 }