In
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...
, a
process
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
* Business process, activities that produce a specific s ...
that is blocked is waiting for some
event, such as a
resource
''Resource'' refers to all the materials available in our environment which are Technology, technologically accessible, Economics, economically feasible and Culture, culturally Sustainability, sustainable and help us to satisfy our needs and want ...
becoming available or the completion of an
I/O operation.
Once the event occurs for which the process is waiting ("is blocked on"), the process is advanced from
blocked state
State most commonly refers to:
* State (polity), a centralized political organization that regulates law and society within a territory
**Sovereign state, a sovereign polity in international law, commonly referred to as a country
**Nation state, a ...
to an imminent one, such as
runnable.
In a
multitasking computer system, individual
tasks, or
threads of execution, must share the resources of the system.
Shared resource
In computing, a shared resource, or network share, is a computer resource made available from one host to other hosts on a computer network.
It is a device or piece of information on a computer that can be remotely accessed from another compu ...
s include: the CPU, network and network interfaces, memory and disk.
When one task is using a resource, it is generally not possible, or desirable, for another task to access it. The techniques of
mutual exclusion
In computer science, mutual exclusion is a property of concurrency control, which is instituted for the purpose of preventing race conditions. It is the requirement that one thread of execution never enters a critical section while a concurr ...
are used to prevent this concurrent use. When the other task is blocked, it is unable to execute until the first task has finished using the shared resource.
Programming language
A programming language is a system of notation for writing computer programs.
Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...
s and
scheduling algorithms are designed to minimize the over-all effect of blocking. A process that blocks may prevent local work-tasks from progressing. In this case "blocking" often is seen as not wanted. However, such work-tasks may instead have been assigned to independent processes, where halting one has little to no effect on the others, since scheduling will continue. An example is "blocking on a
channel" where passively waiting for the other part (i.e. no
polling or
spin loop) is part of the semantics of channels.
Correctly engineered, any of these may be used to implement reactive systems.
Deadlock means that processes pathologically wait for each other in a circle. As such it is not directly associated with blocking.
See also
*
Concurrent computing
Concurrent computing is a form of computing in which several computations are executed '' concurrently''—during overlapping time periods—instead of ''sequentially—''with one completing before the next starts.
This is a property of a syst ...
*
Data dependency
A data dependency in computer science is a situation in which a program statement (instruction) refers to the data of a preceding statement. In compiler theory, the technique used to discover data dependencies among statements (or instructions) i ...
*
Non-blocking algorithm
*
Race condition
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, leading to unexpected or inconsistent ...
*
Scheduling (computing)
In computing, scheduling is the action of assigning resources to perform tasks. The resources may be processors, network links or expansion cards. The tasks may be threads, processes or data flows.
The scheduling activity is carried out b ...
References
Computing terminology
Inter-process communication
Input/output
Scheduling (computing)
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