Nt1210 Chapter 4

Chapter 4
Chapter 4 Review
4.1 Table 3.5 lists typical elements found in a process control block for an unthreaded OS.
Of these, which should belong to a thread control block and which should belong to a process control block for a multithreaded system? Identifiers will appear in both thread and process control blocks, because both need to be identified. Processor State Information should belongs to process control block. Kernel will only interact with process not threads. Process Control Information: Thread control block should handle scheduling and State Information. Data Structuring should also be handled by thread control block (mostly). Memory Management and Resource ownership should belong to process control block.…show more content…
4.4 Give four general examples of the use of threads in a single-user multiprocessing system. Foreground and background work: For example, in a spreadsheet program, one thread could display menus and read user input, while another thread executes user commands and updates the spreadsheet. This arrangement often increases the perceived speed of the application by allowing the program to prompt for the next command before the previous command is complete. Asynchronous processing: Asynchronous elements in the program can be implemented as threads. For example, as a protection against power failure, one can design a word processor to write its random access memory (RAM) buffer to disk once every minute. A thread can be created whose sole job is periodic backup and that schedules itself directly with the OS; there is no need for fancy code in the main program to provide for time checks or to coordinate input and output. Speed of execution: A multithreaded process can compute one batch of data while reading the next batch from a device. On a multiprocessor system, multiple threads from the same process may be able to execute simultaneously. Thus, even though one thread may be blocked for an I/O operation to read in a batch of data, another thread may be…show more content…
4.7 List two disadvantages of ULTs compared to KLTs. 1. In a typical OS, many system calls are blocking. As a result, when a ULT executes a system call, not only is that thread blocked, but also all of the threads within the process are blocked. 2. In a pure ULT strategy, a multithreaded application cannot take advantage of multiprocessing. A kernel assigns one process to only one processor at a time. Therefore, only a single thread within a process can execute at a time. In effect, we have application-level multiprogramming within a single process. While this multiprogramming can result in a significant speedup of the application, there are applications that would benefit from the ability to execute portions of code simultaneously. 4.8 Define jacketing.
The purpose of jacketing is to convert a blocking system call into a non-blocking system call. For example, instead of directly calling a system I/O routine, a thread calls an application-level I/O jacket routine. Within this jacket routine is code that checks to determine if the I/O device is busy. If it is, the thread enters the Blocked state and passes control (through the threads library) to another thread. When this thread later is given control again, the jacket routine checks the I/O device