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A signal is an asynchronous notification sent to a process or to a specific thread within the same process to notify it of an event. Common uses of signals are to interrupt, suspend, terminate or kill a process. Signals originated in 1970s Bell Labs Unix and were later specified in the POSIX standard.
A user thread either runs at user-kernel priority (when it is actually running in the kernel, e.g. running a syscall on behalf of userland), or a user thread runs at user priority. DragonFly does preempt, it just does it very carefully and only under particular circumstances. An LWKT interrupt thread can preempt most other threads, for example ...
The interrupt priority level (IPL) is a part of the current system interrupt state, which indicates the interrupt requests that will currently be accepted. The IPL may be indicated in hardware by the registers in a programmable interrupt controller , or in software by a bitmask or integer value and source code of threads.
In a computer, an interrupt request (or IRQ) is a hardware signal sent to the processor that temporarily stops a running program and allows a special program, an interrupt handler, to run instead. Hardware interrupts are used to handle events such as receiving data from a modem or network card , key presses, or mouse movements.
The Java AWT framework processes all UI changes on a single thread, called the Event dispatching thread. Similarly, all UI updates in the Java framework JavaFX occur on the JavaFX Application Thread. [3] Most network servers and frameworks such as Node.js are also event-driven. [4]
But if the function is used in a reentrant interrupt handler and a second interrupt arises while the mutex is locked, the second routine will hang forever. As interrupt servicing can disable other interrupts, the whole system could suffer. The same function can be implemented to be both thread-safe and reentrant using the lock-free atomics in ...
Current interrupt systems are rather lackadaisical when compared to some highly tuned earlier ones, but the general increase in hardware performance has greatly mitigated this.) Hybrid approaches are also possible, wherein an interrupt can trigger the beginning of some burst of asynchronous I/O, and polling is used within the burst itself.
In many situations it is possible to design data structures that do not require locking, e.g. by using per-thread or per-CPU data and disabling interrupts. Switch to a different thread while waiting. This typically involves attaching the current thread to a queue of threads waiting for the lock, followed by switching to another thread that is ...