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Diffstat (limited to 'doc/src/frameworks-technologies/threads.qdoc')
| -rw-r--r-- | doc/src/frameworks-technologies/threads.qdoc | 29 |
1 files changed, 19 insertions, 10 deletions
diff --git a/doc/src/frameworks-technologies/threads.qdoc b/doc/src/frameworks-technologies/threads.qdoc index 3ef617c..2a0cc1a 100644 --- a/doc/src/frameworks-technologies/threads.qdoc +++ b/doc/src/frameworks-technologies/threads.qdoc @@ -213,10 +213,10 @@ /*! \page threads-reentrancy.html \title Reentrancy and Thread-Safety - + \keyword reentrant \keyword thread-safe - + \previouspage Synchronizing Threads \contentspage Thread Support in Qt \nextpage Threads and QObjects @@ -243,6 +243,15 @@ from multiple threads, even if all the threads use the \e{same} instance of the class. + \note Qt classes are only documented as \e{thread-safe} if they + are intended to be used by multiple threads. If a function is not + marked as thread-safe or reentrant, it should not be used from + different threads. If a class is not marked as thread-safe or + reentrant then a specific instance of that class should not be + accessed from different threads. + + \section1 Reentrancy + C++ classes are often reentrant, simply because they only access their own member data. Any thread can call a member function on an instance of a reentrant class, as long as no other thread can call @@ -268,6 +277,8 @@ end up overwriting each other, and the variable is incremented only once! + \section1 Thread-Safety + Clearly, the access must be serialized: Thread A must perform steps 1, 2, 3 without interruption (atomically) before thread B can perform the same steps; or vice versa. An easy way to make @@ -284,6 +295,8 @@ declared with the \c mutable qualifier because we need to lock and unlock the mutex in \c value(), which is a const function. + \section1 Notes on Qt Classes + Many Qt classes are \e{reentrant}, but they are not made \e{thread-safe}, because making them thread-safe would incur the extra overhead of repeatedly locking and unlocking a QMutex. For @@ -297,9 +310,6 @@ the thread-related classes (e.g. QMutex) and fundamental functions (e.g. QCoreApplication::postEvent()). - \note Qt Classes are only documented as \e{thread-safe} if they - are intended to be used by multiple threads. - \note Terminology in the multithreading domain isn't entirely standardized. POSIX uses definitions of reentrant and thread-safe that are somewhat different for its C APIs. When using other @@ -459,11 +469,10 @@ \list - \o \l{Qt::AutoConnection}{Auto Connection} (default) The behavior - is the same as the Direct Connection, if the emitter and - receiver are in the same thread. The behavior is the same as - the Queued Connection, if the emitter and receiver are in - different threads. + \o \l{Qt::AutoConnection}{Auto Connection} (default) If the signal is + emitted in the thread which the receiving object has affinity then + the behavior is the same as the Direct Connection. Otherwise, + the behavior is the same as the Queued Connection." \o \l{Qt::DirectConnection}{Direct Connection} The slot is invoked immediately, when the signal is emitted. The slot is executed |