Race condition

Race Conditions in Electronics
– Race conditions can occur when logic gates combine signals from different paths.
– Inputs to the gate can change at slightly different times, causing the output to briefly change to an unwanted state.
– If the output functions as a clock signal for systems with memory, it can lead to a departure from the designed behavior.
– A race condition can also occur in logic circuitry used to detect certain outputs of a counter, leading to false matches.
– Design techniques like Karnaugh maps can help recognize and eliminate race conditions.

Types of Race Conditions
– Critical race conditions occur when the order of changing internal variables determines the eventual state of a state machine.
– Non-critical race conditions occur when the order of changing internal variables does not determine the eventual state of a state machine.
– Static race conditions occur when a signal and its complement are combined.
– Dynamic race conditions result in multiple unintended transitions due to interaction between gates.
– Essential race conditions happen when an input has two transitions in less than the total feedback propagation time.

Workarounds for Race Conditions
– Design techniques like Karnaugh maps can help identify and eliminate race conditions.
– Adding logic redundancy can eliminate some types of race conditions.
– Metastable states in logic elements can also cause problems for circuit designers.

Race Conditions in Software
– Race conditions can occur in software when multiple code paths execute simultaneously.
– Different execution times of code paths can lead to unanticipated behavior and software bugs.
– Critical race conditions often occur when processes or threads depend on shared state and fail to follow mutually exclusive access rules.
– Data races are a type of race condition that can result in undefined behavior in C and C++ programs.
– Debugging race conditions can be challenging due to their non-deterministic nature, often referred to as Heisenbugs.

Consequences and Implications of Race Conditions
– Race conditions can lead to security vulnerabilities and denial of service attacks.
– Time-of-check-to-time-of-use (TOCTTOU) bugs can occur when a race condition affects security-sensitive code.
– Race conditions can be intentionally used to create hardware random number generators and physically unclonable functions.
– Privilege escalation can occur when an attacker exploits a race condition to manipulate shared resources.
– Race conditions can result in malfunctioning of actors that utilize a shared resource.
– Race conditions in software can have computer security implications.
– Race conditions in file systems can lead to data corruption or privilege escalation.
– Race conditions in networking can cause issues with distributed chat networks and non-blocking sockets.
– Race conditions in life-critical systems can have disastrous consequences.
– Various tools and techniques are available for detecting and mitigating race conditions in software.

Race condition (Wikipedia)

"Critical race" redirects here. For the academic movement, see Critical race theory.

A race condition or race hazard is the condition of an electronics, software, or other system where the system's substantive behavior is dependent on the sequence or timing of other uncontrollable events. It becomes a bug when one or more of the possible behaviors is undesirable.

The term race condition was already in use by 1954, for example in David A. Huffman's doctoral thesis "The synthesis of sequential switching circuits".

Race conditions can occur especially in logic circuits, multithreaded, or distributed software programs.