Barrier

A barrier or barricade is a physical structure which blocks or impedes something.

Barrier may also refer to:

Physical

Roadway

Crowd and noise control

Barrier (computer science)

In parallel computing, a barrier is a type of synchronization method. A barrier for a group of threads or processes in the source code means any thread/process must stop at this point and cannot proceed until all other threads/processes reach this barrier.

Many collective routines and directive-based parallel languages impose implicit barriers. For example, a parallel do loop in Fortran with OpenMP will not be allowed to continue on any thread until the last iteration is completed. This is in case the program relies on the result of the loop immediately after its completion. In message passing, any global communication (such as reduction or scatter) may imply a barrier.

Dynamic barriers

Classic barrier constructs define the set of participating processes/threads statically. This is usually done either at program startup or when a barrier like the Pthreads barrier is instantiated. This restricts the possible applications for which barriers can be used.

To support more dynamic programming paradigms like fork/join parallelism, the sets of participants have to be dynamic. Thus, the set of processes/threads participating in a barrier operation needs to be able to change over time. X10 introduced the concept of clocks for that purpose, which provide a dynamic barrier semantic. Building on clocks, phasers have been proposed to add even more flexibility to barrier synchronization. With phasers it is possible to express data dependencies between the participating processes explicitly to avoid unnecessary over-synchronization.

Barrier isolator

Barrier isolator is a general term that includes two types of devices: Isolators and Restricted Access Barriers (RABS). Both are devices that provide a physical and aerodynamic (air overpressure) barrier between the external clean room environment and a work process. The isolator design is the more dependable of the two barrier design choices, as it prevents contamination hazards by achieving a more comprehensive separation of the processing environment from the surrounding facility. Nonetheless, both Isolator and RABS designs are contemporary approaches developed over the last 35 years and a great advancement over designs of the 1950s-70s that were far more prone to microbial contamination problems.

Barrier and Isolator designs are used throughout the industries, from sterile injectable drug filling to cytotoxic sterile drug compounding to electronics manufacturing to orange juice filling. Pharmaceutical industry and pharmacy compounding isolators are used for maintaining sterility of a drug, and that is the focus of this article. This type of strict design and control is important when producing sterile medicines because consumers receiving injections, surgical irrigants, or other "parenterally"-administered drugs are often highly vulnerable to infection. As a result, contaminated drugs have caused grave (e.g., permanent injury, death) consequences for the consumer. The sterility of other dosage forms, such as ophthalmics, is similarly important, as blindness or partial loss of vision has occurred due to intrinsically contaminated eye medications.