Many systems implement either the many-to-many or the two-level model place an intermediate data structure between the user and kernel threads. This data structure—typically known as a lightweight process, or LWP—is shown in below Figure. The LWP appears to be a virtual processor on which the application can schedule a user thread to run, to the user-thread library. Each Light Weight Process is attached to a kernel thread, and it is kernel threads that the operating system schedules to run on physical processors. The LWP blocks as well, if a kernel thread blocks (such as while waiting for an I/O ... Read More

One technique for communication between the user-thread library and the kernel is known as scheduler activation. It works as likes: The kernel provides an application with a set of virtual processors (LWPs), and the application can schedule user threads onto an available virtual processor. Moreover, the kernel must inform an application about certain events. This procedure is known as an upcall. Upcalls are handled by the thread library with an upcall handler, and upcall handlers must run on a virtual processor. One event that triggers an upcall occurs when an application thread is about to block. In this scenario, the ... Read More

Threads share the data of the process to which it belongs to. This data sharing provides one of the benefits of multithreaded programming. However, in some circumstances, each thread might need its own copy of certain data. Such data is called thread-local storage (or TLS).For example, in a transaction-processing system, we might service each transaction in a separate thread. Each transaction might be assigned a unique identifier. To associate each thread with its unique identifier, we could use thread-local storage.It is easy to puzzle TLS with local variables. During a single function invocation only local variables are visible, whereas TLS ... Read More

Terminating a thread before it has completed is called Thread cancellation. For an example, if multiple threads are concurrently searching through a database and one thread returns the result, the remaining threads might be canceled. Another situation might be occurred when a user presses a button on a web browser that stops a web page from loading any further. Often, using several threads a web page loads — each image is loaded in a separate thread. When the stop button is pressed by a user on the browser, all threads loading the page are canceled. A thread which is to ... Read More

Signals are software interrupts which sent to a program to indicate that an important event has occurred. A Signal may be handled by following one of two possible handlers:A default signal handlerA user-defined signal handlerA Default signal handler is associated with every signal that the kernel runs when handling that signal. The action that a script or program performs when it receives a signal is called the default actions. A default signal handler handles these types of different default actions.Some of the possible default actions are −Terminate the process.Ignore the signal.Dump core. It creates a file called core containing the ... Read More

Signals are software interrupts which sent to a program to indicate that an important event has occurred. A Signal may be handled by following one of two possible handlers:A default signal handlerA user-defined signal handlerUser-defined signal handler can override this default action that is called to handle the signal. Signals are handled in different ways. Some signals (such as changing the size of a window) are simply ignored; others (such as an illegal memory access) are handled by terminating the program.A signal handler function may have any name, but must have return type void and have one int parameter.Example − ... Read More

Signals are software interrupts which sent to a program to indicate that an important event has occurred. This events can vary from user requests to illegal memory access errors. Some signals, such as the interrupt signal, indicate that a user has asked the program to do something that is not in the usual flow of control. Depending on the source of and the reason for the event being signaled, A Signal can be either synchronously or asynchronously. All signals, whether synchronous or asynchronous, follow the same pattern −The occurrence of a particular event generates a signal.Next, the signal is delivered ... Read More

Pthreads refers to the POSIX standard (IEEE 1003.1c) defining an API for thread creation and synchronization. This defines specification for thread behavior, not an implementation. The specification can be implemented by OS designers in any way they wish. So many systems implement the Pthreads specification; most are UNIX-type systems, including Linux, Mac OS X, and Solaris. Although Windows doesn’t support Pthreads natively, some third-party implementations for Windows are available. The C program shown in Figure 4.9 demonstrates the basic Pthreads API for constructing a multithreaded program that calculates the summation of a nonnegative integer in a separate thread. Separate threads ... Read More

Implicit ThreadingOne way to address the difficulties and better support the design of multithreaded applications is to transfer the creation and management of threading from application developers to compilers and run-time libraries. This, termed implicit threading, is a popular trend today.Implicit threading is mainly the use of libraries or other language support to hide the management of threads. The most common implicit threading library is OpenMP, in context of C.OpenMP is a set of compiler directives as well as an API for programs written in C, C++, or FORTRAN that provides support for parallel programming in shared-memory environments. OpenMP identifies ... Read More

Threads are created in the Windows API using the CreateThread() function, and—just as in Pthreads—a set of attributes like security information, the size of the stack, and a flag for the thread is passed to this function. In the below program, we use the default values for these attributes. (The default values do not initially set the thread to a suspended state and instead make it eligible to be run by the CPU scheduler.) Once the summation thread is created, the parent must wait for it to complete before outputting the value of Sum, as the value is set by ... Read More