3. A file is to be shared among different processes, each of which owns a unique number. The file can be accessed simultaneously by several processes, subject to the following constraint: the sum of the unique numbers owned by the processes currently accessing the file must be less than a defined constant MAX_N. Complete access_file(), finish_access(),

Computer Networking: A Top-Down Approach (7th Edition)
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Problem 3. A file is to be shared among different processes, each of which owns a unique number. The file can be accessed simultaneously by several processes, subject to the following constraint: the sum of the unique numbers owned by the processes currently accessing the file must be less than a defined constant MAX_N. Complete access_file(), finish_access(), and initialization() as below to coordinate file access. (Hint: see an example in Slide 3.39, however, a loop, instead of an ifstatement, is needed in access_file() b/c an resumed process is not guaranteed to have a unique number that works.) 

 

monitor file_access { 

              int curr_sum; //sum of numbers owned by the processes currently accessing the file 

              condition c; //allowing two operations wait() and signal() defined in Slide 3.33

              void access_file(int my_num) {...} //called by a process to request file access 

              void finish_access(int    my_num) {...} //called by a process when completing file access 

               void initialization() {...} //initializing variable(s)

 } 

 

 

 

monitor ResourceAllocator
{ /* <=1 process can be active inside this monitor */
boolean busy; //a local/private variable
condition x; //a local/private variable
void acquire (int time) {
if (busy)
x.wait (time); //suspended, this process is 'waiting'
//when resuming, this process continues
//as if returning from x.wait ()
}
A Monitor to Allocate Single Resource
else
}
busy = TRUE;
}
void release () {
busy = FALSE;
x.signal();
}
void initialization () {
busy = FALSE;
Operating System Concepts-10 Edition
3.39
Silberschatz, Galvin and Gagne ©2018
Transcribed Image Text:monitor ResourceAllocator { /* <=1 process can be active inside this monitor */ boolean busy; //a local/private variable condition x; //a local/private variable void acquire (int time) { if (busy) x.wait (time); //suspended, this process is 'waiting' //when resuming, this process continues //as if returning from x.wait () } A Monitor to Allocate Single Resource else } busy = TRUE; } void release () { busy = FALSE; x.signal(); } void initialization () { busy = FALSE; Operating System Concepts-10 Edition 3.39 Silberschatz, Galvin and Gagne ©2018
Condition Variables
condition x, y; // inside the monitor ADT
Two operations are allowed on a condition variable:
x.wait() a process that invokes the operation is
suspended until another process calls x. signal ()
x.signal () - resumes one of suspended processes (if any)
that previously invoked x. wait ()
▸ The resumed process continues as if it returns from
x.wait ().
▸ If no x. wait () on the variable, then it has no effect on the
variable
Operating System Concepts - 10th Edition
3.33
Silberschatz, Galvin and Gagne ©2018
Transcribed Image Text:Condition Variables condition x, y; // inside the monitor ADT Two operations are allowed on a condition variable: x.wait() a process that invokes the operation is suspended until another process calls x. signal () x.signal () - resumes one of suspended processes (if any) that previously invoked x. wait () ▸ The resumed process continues as if it returns from x.wait (). ▸ If no x. wait () on the variable, then it has no effect on the variable Operating System Concepts - 10th Edition 3.33 Silberschatz, Galvin and Gagne ©2018
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