Threads

A ___________ is a basic unit of CPU utilization; it comprises a thread ID, a program counter (PC), a register set, and a stack.

thread

A thread shares with other threads belonging to the same process its ___________ section, ___________ section, and other operating-system resources, such as open files and signals.

code, data

A traditional process has a ___________ thread of control.

single

If a process has ___________ threads of control, it can perform more than one task at a time.

multiple

Most software applications that run on modern computers and mobile devices are ___________.

multithreaded

An application typically is implemented as a separate ___________ with several threads of control.

process

An application that creates photo ___________ from a collection of images may use a separate thread to generate a thumbnail from each separate image.

thumbnails

A web ___________ might have one thread display images or text while another thread retrieves data from the network.

browser

A word ___________ may have a thread for displaying graphics, another thread for responding to keystrokes from the user, and a third thread for performing spelling and grammar checking in the background.

processor

Applications can also be designed to leverage processing capabilities on ___________ systems.

multicore

Such applications can perform several ___________ tasks in parallel across the multiple computing cores.

CPU-intensive

In certain situations, a single application may be required to perform several ___________ tasks.

similar

For example, a web ___________ accepts client requests for web pages, images, sound, and so forth.

server

A busy web server may have several (perhaps thousands of) clients ___________ accessing it.

concurrently

If the web server ran as a traditional ___________ process, it would be able to service only one client at a time, and a client might have to wait a very long time for its request to be serviced.

single-threaded

One solution is to have the server run as a single ___________ that accepts requests.

process

When the server receives a request, it creates a separate ___________ to service that request.

process

In fact, this - method was in common use before threads became popular.

process-creation

Process creation is ___________ consuming and resource intensive, however.

time

If the new process will perform the same ___________ as the existing process, why incur all that overhead?

tasks

It is generally more ___________ to use one process that contains multiple threads.

efficient

If the web-server process is ___________, the server will create a separate thread that listens for client requests.

multithreaded

When a request is made, rather than creating another ___________, the server creates a new thread to service the request and resumes listening for additional requests.

process

Most operating system ___________ are also typically multithreaded.

kernels

As an example, during system boot time on Linux systems, several kernel threads are ___________.

created

Each thread performs a ___________ task, such as managing devices, memory management, or interrupt handling.

specific

The command ___________ can be used to display the kernel threads on a running Linux system.

ps -ef

Examining the output of this command will show the kernel thread ___________ (with pid = 2), which serves as the parent of all other kernel threads.

kthreadd

Many applications can also take advantage of ___________ threads, including basic sorting, trees, and graph algorithms.

multiple

In addition, programmers who must solve contemporary - problems in data mining, graphics, and artificial intelligence can leverage the power of modern multicore systems by designing solutions that run in parallel.

CPU-intensive

___________ an interactive application may allow a program to continue running even if part of it is blocked or is performing a lengthy operation, thereby increasing responsiveness to the user.

Multithreading

This quality is especially useful in designing ___________ ___________.

user interfaces

Processes can share resources only through techniques such as ___________ ___________ and message passing.

shared memory

However, threads share the ___________ and the resources of the process to which they belong by default.

memory

The benefit of sharing code and data is that it allows an application to have several different threads of activity within the same ___________ ___________.

address space

Allocating memory and resources for process creation is ___________.

costly

Because threads share the resources of the process to which they belong, it is more ___________ to create and context-switch threads.

economical

Empirically gauging the difference in ___________ can be difficult, but in general thread creation consumes less time and memory than process creation.

overhead

Additionally, ___________ ___________ is typically faster between threads than between processes.

context switching

The benefits of multithreading can be even greater in a ___________ architecture, where threads may be running in parallel on different processing cores.

multiprocessor

A ___________ process can run on only one processor, regardless how many are available.

single-threaded

Every process has ___________ or more threads, allowing the same process to perform multiple tasks concurrently.

one

Each thread executes ___________ of one another and therefore each thread requires its own stack.

independently

A ___________ process or program that has only one thread of control (and so executes on only one core at a time).

single-threaded

___________: A term describing a process or program with multiple threads of control, allowing multiple simultaneous execution points.

multithreaded

Earlier in the history of computer design, in response to the need for more computing performance, ___________-CPU systems evolved into multi-CPU systems.

single

A later, yet similar, trend in system design is to place multiple computing ___________ on a single processing chip where each core appears as a separate CPU to the operating system (Section Multiprocessor systems).

cores

We refer to such systems as ___________, and multithreaded programming provides a mechanism for more efficient use of these multiple computing cores and improved concurrency.

multicore

On a system with a single computing core, ___________ merely means that the execution of the threads will be interleaved over time (animation titled Concurrent execution on a single-core system), because the processing core is capable of executing only one thread at a time.

concurrency

On a system with multiple cores, however, concurrency means that some threads can run in ___________, because the system can assign a separate thread to each core (animation titled Parallel execution on a dual-core system).

parallel

___________ means all threads make progress on a single-core system as each thread gets to run for a short period of time on the single processing core.

Concurrency

___________ allows two threads to run at the same time as each thread runs on a separate processing core.

Parallelism

Notice the distinction between ___________ and parallelism in this discussion.

concurrency

A ___________ system supports more than one task by allowing all the tasks to make progress.

concurrent

In contrast, a ___________ system can perform more than one task simultaneously.

parallel

Thus, it is possible to have ___________ without parallelism.

concurrency

Before the advent of ___________ and multicore architectures, most computer systems had only a single processor, and CPU schedulers were designed to provide the illusion of parallelism by rapidly switching between processes, thereby allowing each process to make progress.

multiprocessor

Such processes were running ___________, but not in parallel.

concurrently

The trend toward multicore systems continues to place pressure on system designers and application programmers to make better use of the multiple computing ___________.

cores

Designers of operating systems must write ___________ ___________ that use multiple processing cores to allow the parallel execution shown in the animation titled Parallel execution on a dual-core system.

scheduling algorithms

For application programmers, the challenge is to modify existing programs as well as design new programs that are ___________.

multithreaded

This involves examining applications to find areas that can be divided into separate, ___________ tasks.

concurrent

Ideally, tasks are ___________ of one another and thus can run in parallel on individual cores.

independent

While identifying tasks that can run in parallel, programmers must also ensure that the tasks perform ___________ work of equal value.

equal

Just as applications are divided into separate tasks, the ___________ accessed and manipulated by the tasks must be divided to run on separate cores.

data

The data accessed by the tasks must be examined for ___________ between two or more tasks.

dependencies

When one task depends on data from another, programmers must ensure that the ___________ of the tasks is synchronized to accommodate the data dependency.

execution

When a program is running in parallel on multiple cores, many different ___________ paths are possible.

execution

___________ and debugging such concurrent programs is inherently more difficult than testing and debugging single-threaded applications.

Testing

Amdahl's Law is a ___________ that identifies potential performance gains from adding additional computing cores to an application that has both serial (nonparallel) and parallel components.

formula

If S is the portion of the application that must be performed ___________ on a system with N processing cores, the formula appears as follows: speedup≤S+N(1−S)​1​

serially

The ___________ portion of an application can have a disproportionate effect on the performance we gain by adding additional computing cores.

serial

In general, there are two types of parallelism: data parallelism and ___________ parallelism.

task

___________ parallelism focuses on distributing subsets of the same data across multiple computing cores and performing the same operation on each core.

Data

___________ parallelism involves distributing not data but tasks (threads) across multiple computing cores.

Task

Each thread is performing a ___________ operation.

unique

Fundamentally, then, data parallelism involves the ___________ of data across multiple cores, and task parallelism involves the distribution of tasks across multiple cores, as shown in Figure 4.2.1.

distribution

A ___________ system allows more than one task to run simultaneously.

parallel

___________ involves distributing tasks across multiple computing cores.

Task parallelism

___________: Multiple processing cores within the same CPU chip or within a single system.

multicore

___________: A computing method that distributes subsets of the same data across multiple cores and performs the same operation on each core.

data parallelism

___________: A computing method that distributes tasks (threads) across multiple computing cores, with each task is performing a unique operation.

task parallelism

Support for threads may be provided either at the ___________ level, for user threads, or by the kernel, for kernel threads.

user

___________ threads are supported above the kernel and are managed without kernel support, whereas kernel threads are supported and managed directly by the operating system.

User

Virtually all contemporary operating systems—including ___________, ___________, and macOS—support kernel threads.

Windows, Linux

The -to- model maps many user-level threads to one kernel thread.

many-to-one

Thread management is done by the thread ___________ in user space, so it is efficient (we discuss thread libraries in Section 4.4).

library

However, the entire process will ___________ if a thread makes a blocking system call.

block

Also, because only one thread can access the kernel at a time, multiple threads are unable to run in ___________ on multicore systems.

parallel

___________ threads—a thread library available for Solaris systems and adopted in early versions of Java—used the many-to-one model.

Green

The -to- model maps each user thread to a kernel thread.

one-to-one

It provides more ___________ than the many-to-one model by allowing another thread to run when a thread makes a blocking system call.

concurrency

It also allows multiple threads to run in parallel on ___________.

multiprocessors

The only drawback to this model is that creating a user thread requires creating the corresponding ___________ thread, and a large number of kernel threads may burden the performance of a system.

kernel