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Topic: Busy-wait

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CSci 444/544, Fall 2005 Homework #1 One of pros of busy waiting is that it is efficient in cases where the expected wait time is less than the overhead of context switching out of and back to the waiting thread. Busy waiting can be avoided in a synchronization primitive if the primitive always performs a yield whenever an unavailable lock is needed. By definition a busy wait just spins on the CPU until the lock becomes available, and perhaps these cycles could be used for some other computation. www.cs.wm.edu /~dsn/courses/444/homework/hw1sol.html

CS411/511 - Homework Busy waiting: A process is waiting for an event to occur and it does so by executing instructions. Other types of waiting: A process is waiting for an event to occur in some waiting queue (e.g., I/O semaphore) and it does so without having the CPU assigned to it. To prove bounded waiting, we note that whenever a process leaves its critical section, it checks to see if any other processes want to enter their critical sections. web.engr.oregonstate.edu /~pancake/cs411/hw4sol.s99.html

servicing.html The waiting time for this job is then the service time the processor had at the time of assignment. If busy processors reject requests as they arrive, then we have to reject the second request, if it comes within the time it takes to serve the first request. When all processors are busy, we assign the job to the processor with the smallest service time. www.math.uic.edu /~jan/mcs494f02/Lec5/servicing1.html

Semaphore (programming) - Open Encyclopedia A process wishing to execute an operation that is already being executed by another process must wait for it to complete first. P(Semaphore s) { while (s <= 0) ; /* wait until s>0 */ s = s-1; /* must be atomic operation */ } The P and V operations must be indivisible, which means that each of the operations may not be executed multiple times concurrently. open-encyclopedia.com /Semaphore_(programming)

Monitor (synchronization) - Wikipedia, the free encyclopedia To avoid entering a busy waiting state, processes must be able to signal each other about events of interest. Note that since waiting on a condition forfeits the lock, the waiter must make sure the monitor invariant is satisfied before it waits. In early monitor implementations, notifying a condition variable caused a waiting process to receive the lock and run immediately, thereby guaranteeing that the condition would still be true. en.wikipedia.org /wiki/Condition_variable

[SDL] bomber busy waiting? If you wanted to wait As regards the sound stuff there is no busy waiting in my code, it is just the SDL audio callback that I wrote. In mainline code I think I busy wait to get the timer interrupt, forcing frame rate to 25 hz, but only under Win32. Sam wrote: >What you have in bomberman is busy waiting. www.libsdl.org /pipermail/sdl/1999-July/021398.html

Skycasters Broadband Satellite Internet-Dealer Information Businesses are continuing to increase their use of the Internet for e-commerce, email, a research and reference source for any subject, a travel agent, a stock ticker, an encyclopedia, a worldwide phone book and much, much more. Every day, companies turn to the Internet to match the changing business practices of their suppliers and customers, who are choosing to conduct as much business as possible over the Internet as a way to reduce operating and sales costs. This tremendous increase in business Internet access is the result of a continuing nationwide landslide of businesses seeking always-on, high-speed Internet connections that can be shared among multiple users in a single office. www.skycasters.com /dealer-info.html

Busy Waiting The remaining processes each become livelocked in their busy wait loop. The algorithm is that each process should first wait for all other processes to clear their critical sections, then declare their own intention to enter (the intention being to exclude all other processes from entering), then enter, then relinquish their intention after clearing the critical section. The problem is that after waiting for all other processes to clear their critical sections a process may not be able to get into theirs before another process does so. www.dcs.warwick.ac.uk /~sgm/cs237/lec/busy

Interpreting Wait Events This was the longest buffer busy wait for this statement, as indicated by the "Max. From this we concluded that the buffer busy waits appeared related to the single block disk reads-buffer block reads were waiting for other buffer block reads to complete, and those in turn were waiting for sequential reads from disk to complete. Waits on db file sequential read and db file scattered read combined were significantly shorter than the waits on db file sequential read in the original query because large numbers of single block I/Os were replaced with fewer multi-block I/Os. www.pafumi.net /Wait_Events.html

CS67 Operating Systems Busy Waiting / Blocking Busy waiting and blocking are both ways a process can wait for an event to occur. Blocking is a much better way to wait for an event since it does not consume CPU cycles like busy waiting does. In busy waiting, the process repeatedly checks to see if the event has occurred. www.cs.siena.edu /~flatland/exam1sol.html

lecFeb17.html On a multiprocessor, busy waiting is not as wasteful and may be an option for short waits. The introduction of busy waiting appeared to solve the original problem of the two threads - the "producer" that incremented x and the "consumer", that printed each new value of x. On a uniprocessor, busy waiting is wasteful of cpu cycles. condor.depaul.edu /~glancast/374class/docs/lecFeb17.html

cis34508.txt If wait is expected to be short, busy waiting is used in form of a spin lock. Mutex lock is particularly useful for threads because it is not busy waiting. The solution using TSL is correct, but does require the use of busy waiting. grail.cba.csuohio.edu /~jackie/cis345a/notes/cis34508.txt

lecture7.html Processes that are busy waiting use their whole quantum doing nothing (if they're waiting, the process actually in its critical section can't be advancing...). Not only can busy waiting be inconvenient, on systems with a priority scheduler priority inversions can occur. Processes waiting to enter a critical section will be put in the blocked state, just like they were waiting for I/O, so that other processes can continue doing useful work. www.isi.edu /~faber/cs402/notes/lecture7.html

index.html Busy Waiting: If a process is denied access to its critical section, it will continue to check again and again until it can enter its critical section. Busy waiting waste valuable processor time, and in some cases can cause deadlock. This continuous checking of the lock variable is called busy waiting. www.ualr.edu /xxliu3/thirdp.htm

lecture_6_mutual_exclusion.doc value = 0; Lock::Acquire() { while (test_and_set(value) == 1); } Lock::Release() { value = 0; } Busy-Waiting The problem with both of the existing interrupt disable and test_and_set solutions is busy-waiting, or consumption of CPU cycles while a thread is waiting for a lock. Also, inside the waiting loop, interrupts are enabled first so that someone else may have a chance to release the lock. If the lock is free, the value of the lock is set to BUSY, and interrupts are re-enabled. www.cs.fsu.edu /~awang/courses/cs111/lecture_6_mutual_exclusion.doc

Busy Waiting Mutual exclusion policies that require busy waiting waste valuable processor time, and in some cases can lead to situations where a process will test the lock variable forever, a very undesirable occurence. This continuous testing of the lock variable is called busy waiting. In other words, as long as a process is denied access to its critical section, it will stay in a tight loop and wait until it can proceed, all the while wasting processor time. cne.gmu.edu /modules/ipc/red/busy.html

IBM Redbooks XES Coupling Facility Subchannel Tuning The effect of this should be that when a request is started, rather than being given a subchannel and then spinning waiting for a link buffer to become available, the request may receive subchannel busy (because fewer subchannels are available) and the request will be converted to an asynchronous request. This may result in longer response times for those requests that can't get a subchannel; however, it should result in less CPU overhead due to waiting for busy links. Because MVSW is receiving a higher percentage of path busy conditions (about 400%!), XES on MVSW has varied 4 of its subchannels offline in an effort to reduce the amount of time it is receiving path busy when it tries to use one of the links. www.redbooks.ibm.com /Redbooks.nsf/ffb155b535b4144485256c050061937a/c533df2d6aedfb8d85256d25004cf328?OpenDocument&printable

THIS IS THE JARGON FILE, VERSION 3.2.0, 21 MAR 1995 Technically, `busy-wait' means to wait on an event by {spin}ning through a tight or timed-delay loop that polls for the event on each pass, as opposed to setting up an interrupt handler and continuing execution on another part of the task. Used of human behavior, conveys that the subject is busy waiting for someone or something, intends to move instantly as soon as it shows up, and thus cannot do anything else at the moment. This is a wasteful technique, best avoided on time-sharing systems where a busy-waiting program may {hog} the processor. www.unb.ca /web/samples/jargon.cgi?busy-wait

answers.1 TSL is a busy waiting lock that is normally used for waiting for a very short period of time to enter a short critical section. The answers to assignment number 1 : ------------------------------------ *********** ** 2.3 ** *********** With busy waiting, a process keeps testing for some condition. With blocking, a process gives up the CPU and is awakened later when the condition it is waiting for has become true. www.cis.syr.edu /courses/CIS657/answers.1

CS 162 Sec 101 Spring 2002: Notes 19 Feb Keep busy waiting to a minimum; don’t busy wait for the entire time someone else holds the lock, just busy wait for enough time to tell that someone else holds the lock by checking a guard variable. In a priority-based CPU scheduler, the waiting thread might be higher priority while the lock holder might be lower priority, so that lock holder never gets to run and release the lock. This donation should propagate to thread 1 since thread 2 is waiting on it, so that both thread 2 and 1 should have an effective priority of 3. www.ocf.berkeley.edu /~jerylkat/cs162/cs162_101notes19feb.html

iluvpinkpanther : again sry been busy.. been waiting aroun been waiting around for chris to call but he hasnt he came back home today!!! www.greatestjournal.com /go.bml?journal=iluvpinkpanther&itemid=1563&dir=next

LWN: Patch: IDE probe & waiting for busy - Waiting for busy means we could eventually end up waiting for a crappy command, we shall rather interrupt whatever the drive is doing via a execute diagnostics command. My idea here is that in real life, we don't have to deal with the case where the drive is already running some command. More than that, on typical embedded setups, the kernel may be booted right from flash with almost no firmware work and so will inherit from devices coming right from HW reset. lwn.net /Articles/10520

Fight Or Flight Two shaky breaths later, and Oliver became aware of the fact that he had been too busy waiting for his heart to implode and splatter his ribs and kidneys and the rest of the inside of his chest to actually make out what was said. The wood, it was coming through the wood, from outside on the classroom floor, and Percy was not dead, not a ghost, just whispering, said his instincts, but bugger it all, they had lead him to a bleeding cupboard of all things. www.geocities.com /wanderbymistake/fightorflight.html

race.txt If context switch occurs between " busy = FALSE " and " if wait_to_read then V(rdr) ", and if a writer comes and gets CPU, it will enter the C.S. because readcount = 0 and busy = false. The initial value should be 0, and the absolute value of the semaphore represents the number of processes waiting. Do not release mutex, as it is being "granted" to the waiting process. www.ee.umd.edu /courses/enee648i/race.txt

Anime News Network - Encyclopedia We had planned to resolve this by getting the help of two new staff members, but I've been so busy that I haven't had the time to properly brief them on how to use the various administration tools. Needless to say, moving to a new place can get pretty busy, and moving to a new country doubly so. Yes, that's right, yours truly has found a job in the land of the rising sun. www.animenewsnetwork.com /encyclopedia

Lecture 3 - Too Much Milk; Hardware Synchronization; Semaphores To eliminate busy waiting, we need some mechanism to make waiting threads go to sleep and some way to wake a sleeping thread up when the lock is available. There is no way to eliminate busy waiting altogether, but you only busy wait to atomically check the lock value. The problem with this apparently simple configuration is that it is still busy waiting. www-scf.usc.edu /~csci402/crowley/lect3.html

Simdlreport.doc In this structure a generator produces the calls, and sends them to the minimum possible indexed waiting_line queue satisfying the condition that that queue is empty and corresponding telephone is not busy. While a server is serving a call, the status of that telephone is set to busy (using phone array) until it finishes serving in order to declare that specified telephone is still busy. I have 6 queues named as waiting_line[6] where first 5 are for the 5 telephones and the last one is to put abandoned calls. www.geocities.com /nuritike/dersler_odevler/Ceng476/Simdlreport.doc

3.2.0.1 Synchronized methods and statements We can program a Java thread so that it busy waits on a locked object, but this is almost always a bad programming practice. puts the calling thread to sleep on a queue of threads that are waiting for some change in the status of a locked object. is invoked for the locked object, a check is done to see whether any change has been made to it, and then some waiting thread from the associated queue is allowed to run. www.cs.rice.edu /~cork/teachjava/2003/notes/current/node97.html

Excel Pausing or waiting on busy :: MrExcel Message Board I would like to have a way to wait between the two ActiveWindow.Close statements until the the system is no longer busy with the save. The problem is that because the system is busy saving the frist work book, when I do the ActiveWindow.Close SaveChanges:=False for the second workbook, I get a Excel has caused an error and needs to shut down. The "True" portion then tells it to wait until control is returned to Excel before continuing with the macro. www.mrexcel.com /archive2/8800/9875.htm

manquery - -s 9f drv_usecwait @ Eastern Illinois University The amount of time spent busy- waiting may be greater than the microsecond count but will minimally be the number of microseconds specified. First, the granularity of the wait time is limited to one clock tick, which may be more time than is needed for the delay. Often, drivers need to delay for only a few microseconds, waiting for a write to a device register to be picked up by the device. www.eiu.edu /cgi-bin/manquery?drv_usecwait(9f)

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