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There are two distinct models of thread controls, and they are user-level threads and kernel-level threads. The thread function library to implement user-level threads usually runs on top of the system in user mode. Thus, these threads within a process are invisible to the operating system. User-level threads have extremely low overhead, and can achieve high performance in computation. However, using the blocking system calls like read(), the entire process would block. Also, the scheduling control by the thread runtime system may cause some threads to gain exclusive access to the CPU and prevent other threads from obtaining the CPU. Finally, access to multiple processors is not guaranteed since the operating system is not aware of existence of these types of threads. On the other hand, kernel-level threads will guarantee multiple processor access but the computing performance is lower than user-level threads due to load on the system. The synchronization and sharing resources among threads are still less expensive than multiple-process model, but more expensive than user-level threads. Thus, user-level thread is better than kernel level thread.
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Difference between kernel mode and user mode?
Kernel ModeIn Kernel mode, the executing code has complete and unrestricted access to the underlying hardware. It can execute any CPU instruction and reference any memory address. Kernel mode is generally reserved for the lowest-level, most trusted functions of the operating system. Crashes in kernel mode are catastrophic; they will halt the entire PC.User ModeIn User mode, the executing code has no ability to directly access hardware or reference memory. Code running in user mode must delegate to system APIs to access hardware or memory. Due to the protection afforded by this sort of isolation, crashes in user mode are always recoverable. Most of the code running on your computer will execute in user mode.
Difference between Java threads and user level thread?
A Java thread can be considered as similar to a user level thread. Let us say you are running a web browser, windows media player and GTalk for chat simultaneously - Actually the operating system is running an individual thread for each of these apps which gives you a seamless feeling of things running in parallel. Similarly Java Threads are features in the Java programming language that allow you to run multiple JVM tasks in parallel.
In an amp What is better high or low signal to noise ratio?
Signal to noise ratio is the difference between the noise floor and the reference level.
What is the difference between a Parent Process and Foreground Process?
A parent process is a process that has spawned one or more child processes such that it takes "ownership" of those processes. A foreground process typically means a process that has a user-interface as opposed to a background process which typically does not. Most background processes are services while most foreground processes are applications. It's important to note that the term "process" has a specific meaning in a multi-processing environment. A process is a computer program that has one or more threads of execution. A thread is the machine-level representation of a task and a process may instantiate as many tasks as are required (hardware permitting). All tasks share the same memory space as the process itself, however each task has its own stack for local storage, as well as to enable the thread's function call-and-return mechanism in addition to thread-local exception handling. Every process must have at least one thread of execution typically referred to as the main thread because that is the thread that executes the program's global main function (the entry point of the application) and subsequently instantiates any additional threads required by the main thread. The additional threads are usually called worker threads and any thread can instantiate its own worker threads. Unlike parent/child processes, thread's cannot "own" other threads; the threads are owned by the process. However, it is possible for worker threads to be controlled by other threads in the same process, so in that sense the controlling thread can be said to be a parent thread. When the main function returns, the main thread terminates, however any active threads within the process will continue executing, thus keeping the process "alive". In many cases this would be undesirable particularly if those threads attempt to access shared memory that is released by the main thread. So although there is no notion of ownership amongst threads, any controlling thread that must terminate before its workers have completed their tasks should signal its workers to terminate and then wait for them to terminate before terminating itself. Threads of execution within a process execute concurrently. All this means is that the operating system's task scheduler gives each thread a time-slice of the CPU to do some work, before saving the thread's state and moving onto the next thread (which may belong to another process entirely). Task-switching is so rapid that it can appear as though all threads are executing simultaneously, however that is only physically possible when the CPU has 2 or more cores available. Only one thread may execute upon any single core at any given moment. Multiple threads are typically used to maintain responsiveness. In a GUI environment, a time-consuming task would take up the entire time-slice of a process so it won't be able to respond to any messages on the message queue unless the task specifically checks the queue periodically. However, by using a worker thread to carry out the task, the controlling thread can remain responsive to messages. The message queue can also be used by threads to signal other threads, thus a controlling thread can respond to periodic progress reports from its worker threads if required. In this sense it can be said that the worker threads are background tasks, while the controlling thread is the foreground task.
What is thread class in java?
The ability of a program to concurrently execute multiple regions of code provides capabilities that are difficult or impossible to achieve with strictly sequential languages. Sequential object-oriented languages send messages (make method calls) and then block or wait for the operation to complete. Programmers are already familiar with concurrent processes, possibly without recognizing them. For example, operating systems usually have many processes running to handle printing, updating the display, receiving mail from the network, and so on. In contrast, most programming languages do not promote the use of concurrent operations within one application. At best, programmers have access to a few library calls to launch and control multiple operations. Java provides language-level and library support for threads--independent sequences of execution within the same program that share the same code and data address space. Each thread has its own stack to make method calls and store local variables. Most applications that use threads are a form of simulation or have a graphical user interface, but threads in general have the following advantages over sequential programming: Threads support concurrent operations. For example, Server applications can handle multiple clients by launching a thread to deal with each client. Long computations or high-latency disk and network operations can be handled in the background without disturbing foreground computations or screen updates. Threads often result in simpler programs. In sequential programming, updating multiple displays normally requires a big while-loop that performs small parts of each display update. Unfortunately, this loop basically simulates an operating system scheduler. In Java, each view can be assigned a thread to provide continuous updates. Programs that need to respond to user-initiated events can set up service routines to handle the events without having to insert code in the main routine to look for these events. Threads provide a high degree of control. Imagine launching a complex computation that occasionally takes longer than is satisfactory. A "watchdog" thread can be activated that will "kill" the computation if it becomes costly, perhaps in favor of an alternate, approximate solution. Note that sequential programs must muddy the computation with termination code, whereas, a Java program can use thread control to non-intrusively supervise any operation. Threaded applications exploit parallelism. A computer with multiple CPUs can literally execute multiple threads on different functional units without having to simulating multi-tasking ("time sharing"). On some computers, one CPU handles the display while another handles computations or database accesses, thus, providing extremely fast user interface response times.
