From Wikipedia, the free encyclopedia.
A race hazard (or race condition) is a flaw in a system or process where the outcome is determined by which of two or more equally likely conditions arise, which is not the intended design outcome. The term originates with the idea that two signals are racing each other to be the first to cause the output.
Race hazards are found in poorly designed electronics systems, especially logic circuits, but they may also arise in computer software.
A typical example of a race hazard is in a system of logic gates, where inputs are changing. If a particular output depends on the state of the inputs, it may only be defined for steady-state signals. As the inputs change state, there is a finite delay before the output will change, due to the physical nature of the electronic system. For a brief period, the output may change to an unwanted state before settling back to the designed state. For many systems, such glitches can be tolerated, but if for example this output signal is used to act as a clock for further systems that contain memory, the system can rapidly depart from its designed behaviour. Proper design techniques (e.g. Karnaugh maps - note, the Karnaugh map article includes a concrete example of a race hazard and how it can be eliminated) ensure that race hazards are acknowledged and eliminated before they can become a problem.
Race hazards may arise in software, especially when communicating between separate processes or threads of execution. For example, one process may require the change of state of a flag from another process before it can continue, but a similar dependency in the other direction exists - the second priocess requires a signal from the first before it can continue. The result is deadlock - neither process can continue and both come to a halt. Again, proper design is the correct way to eliminate such situations.Electronics
Computing
