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chapter 5 concurrency control, requires a majority vote, meaning a participant must recieve granted from majority of the vote to enter into it's critical region, mutual exclusion by not allowing more than one process within the monitor to be active at any given time. , 1.does it ensure two processes will not enter their critical regions at the same time? yes 2.does it prevent interference from processes not attempting to enter thier critical region? no and yes -the unanimous decision fails and the majority vote passes 3. does it prevent starvation? yes, it ensure that multiple processes that share resources do not attempt to share the same resource at the same time. -is necessary for resources such as tape drivers, printers, and files., do semaphores prevent starvation? yes, do monitors prevent starvation?yes, unlocked , do monitors prevent interference from process not attempting to enter their critical regions? yes, does it prevent interference from processes not attempting to enter their critical regions? yes, -who receives such messages -who sends such messages -what is necessary to enter a critical region, 1. how do you determine if the token is lost or just being used for a long time? 2. what happens if the location processing the token crashes for an extended period of time? 3. how do we maintain a logical ring if a processor drops out of the system? 4.how do we identify and add processors joining the logical ring?, 1.request-request to enter critical region may be done individually sent or by group communication mechanism. message travels from sender to all participants in sysem. 2.oueued-(optional)-it can be used to notifythe process that the request has been received and to expect a message whenever the request can proceed to the next step. -it is used whenever a request cannot be granted immediately. 3.granted-sent to all participants for two reasons (1)if that location is not in its critical region and does not have a request with an earlier timestamp, it will send granted . (2) when a location has queued upon completion of its critical region, -reliance on programmer, who could make a mistake causing a dealock -their dependance on programer to raise and lower , atomic operations -which uses an atomic operation (indivisible), token-passing is intended for the use with multiple processors connected via a network(parallel or distributed) -consists of a single token and a path traveling through all of the processors a logical ring - to enter the critical region, a process must possess this token.(only one token) -when a process exits the critical region the token is release back into the system., semaphores -a type of integer variable whose value indicates the status of the protected resource, unlike centralized, there is no absolute permission.disturbd lock manager algorithms granted , is a vote to grant permission. a participant must recieve a granted vote from every participant to enter the critical region., chapter 5 concurrency control -concurrency control keeps processes out of each other's way and ensures a smooth and proper execution in a distributed computing, check and set test and lock - makes impossible for another process to perform any operation intertwined within the checking of lock and setting of the lock., swap -is able to swap out the current value of the lock state with a value indicating that the shared resource is now in a locked state., does it prevent starvation? no, is a process does not want to enter critical region it will starve because it's value will not change, does it prevent starvation? yes, prevent-one of the four allocation conditions avoid- using algorithims to get system needs first in order to see if it can be done. ignore the deadlock detect-focuses on finding a deadlock after it has occurred, taking turns -the processes take turns entering their critical region, distributed , three point test, -the portion of code or program accssing a shared resource. only such a needs to prohibit concurrency (concurrency control), do monitors ensure that two processes will not enter their regions at the same time? yes, centralized -using this creates a single critical element and single point of failure, thereby making this approach unviable for disturbed real-time applications. -this server maintains information concerning what processes have requested to enter their critical regions and what process has been granted access., is difficult in truly distributed environment and are generally best avoided since absolute consistency of the semaphores data most be maintained., does it ensure mutual exclusion? yes, -when the process want enter a critical region of code, executes lower, mutual exclusion and critical regions, have two operations raise and lower -both check the value of the semaphore and either increase it by 1 or decrease it by 1, monitors -which is a complier supported programming language constuct that allows a group of procedures, their variables, and the data structure to be grouped together in a package or module it is an abstract data type., does it ensure that two proceses will not enter their critical regions at the same time?yes, -when the process want enter a critical region of code, it executes raise, do semaphores ensure that two processes don't enter thier critical regions at the same time? yes, deadlocks mutual exclusion is one of the factors that causes deadlocks.the other's are(2)non-preemptive resource allocation-when system can't force process to relinquish control of the resource(3) hold and wait- when a process holds one resource and is waiting on another resource.(4)cyclic wait-requires (3),a resource will not be released until the process obtains a resource currently held by another member in this cycle. , does it prevent interference from processes not attempting to enter their critical regions? no -if a process never wants to go into the critical region, it interfere's with another process, locked , do semaphores prevent interference form porcess that have expressed a desire to enter the critical region? yes, 1. request- requesting entry into it critical region 2.queued-(optional)- use when immediate access can not be granted 3. granted- a message sent giving permission to enter into critical region 4. release-indicates that process has been completed and the lock is been released., 1. does it ensure mutual exclusion yes 2. does it prevent interference from other processes attempting to enter their critical region yes 3.does it prevent starvation yes, this would require a unanimous decision, it is unacceptable, locks -can be used to keep other processes from utilizing a shared resource., 1. does it ensure mutual exclusion yes 2. does it prevent interference from other processes attempting to enter their critical region yes 3.does it prevent starvation yes