/OSN-Assignment-5

Primary LanguageC

Notes to evaluator:

  1. I have created a total of 2 semaphores, wm which holds the value of the number of free washing machines, and mutex(mutex lock) which locks global variables when being modified by one thread.

  2. The algorithm followed is as follows:

  • We initialise 1 pthread for each of the 'n' students at the beginning.
  • The pthread executes a function wash, in which there is initially a sleep() for T_i seconds until the student arrives at the scene.
  • After he/she arrives, the wm semaphore is checked to identify if any washing machine is free to use. If it is not, then the student will wait for P_i seconds for a machine to get empty, else leave w/o washing. This has been implemented using the sem_timedwait function (returns -1 if semaphore is <=0 after it reaches a given timestamp).
  • When the wm semaphore value is > 0, i.e. if a washing machine is free to use, the student starts washing and semaphore is decremented. We implement sleep(W_i) before incrementing the semaphore to simulate the washing time.
  • In all such cases, the waiting time of every student is added up to a global variable, and also the count of students who left w/o washing.

  1. FCFS is always followed. However there are certain cases like in sample output 1, Student 1 & 3 arrive at the same time. So the order on which pthread is created first is non-deterministic (depending on whether the processor follows FCFS or not) and hence outputs could vary in the 2 cases. However, if Student 1 comes before student 3 and both are waiting, Student 1 WILL use a washing machine before 3, neglecting patience issues. No queue has been used for FCFS.

  2. Let us say if Student 4 is going to finish washing at 5s, and Student 1 is waiting since 2s to wash, with a patience of 3s. Now we are going to assume that Student 4 will finish washing before Student 1's patience gets exhausted in all inputs having such a case. Thus, to simluate this, we give a slight delay of 0.1s to Student 1 in such a case.

  3. The number on the LHS of the output indicates the timestamp at which the checkpoint has occured.

  4. Colouring of outputs has been done using printf statements only.

  5. The bonus in Q1 has been done as well.