Typical Uses
The RAII technique is often used for controlling mutex locks in multi-threaded applications. In that use, the object releases the lock when destroyed. Without RAII in this scenario the potential for deadlock would be high and the logic to lock the mutex would be far from the logic to unlock it. With RAII, the code that locks the mutex essentially includes the logic that the lock will be released when the RAII object goes out of scope.
Another typical example is interacting with files: We could have an object that represents a file that is open for writing, wherein the file is opened in the constructor and closed when the object goes out of scope. In both cases, RAII only ensures that the resource in question is released appropriately; care must still be taken to maintain exception safety. If the code modifying the data structure or file is not exception-safe, the mutex could be unlocked or the file closed with the data structure or file corrupted.
Ownership of dynamically allocated objects (memory allocated with new in C++) can also be controlled with RAII, such that the object is released when the RAII object is destroyed. For this purpose, the C++11 standard library defines the smart pointer classes std::unique_ptr for single-owned objects and std::shared_ptr for objects with shared ownership. Similar classes are also available through std::auto_ptr in C++98, and boost::shared_ptr in the Boost libraries.
Read more about this topic: Resource Acquisition Is Initialization
Famous quotes containing the word typical:
“It is indeed typical that you Earth people refuse to believe in the superiority of any world but your own. Children looking into a magnifying glass, imagining the image you see is the image of your true size.”
—Franklin Coen. Joseph Newman. The Monitor (Douglas Spencer)
“Compare the history of the novel to that of rock ‘n’ roll. Both started out a minority taste, became a mass taste, and then splintered into several subgenres. Both have been the typical cultural expressions of classes and epochs. Both started out aggressively fighting for their share of attention, novels attacking the drama, the tract, and the poem, rock attacking jazz and pop and rolling over classical music.”
—W. T. Lhamon, U.S. educator, critic. “Material Differences,” Deliberate Speed: The Origins of a Cultural Style in the American 1950s, Smithsonian (1990)