Threas&Concurrency

Definition

• Instance of a program An instance of a program is a copy of an executable version of the program that has been written to the computer’s memory.

• Process When we run a program, those instructions are copied into memory and space is allocated for variables and other stuff required to manage its execution. This running instance of a program is called a process and it’s processes which we manage.

Top

What do we need to support threads?

thread data structure

mechanisms to create and manage threads

mechanisms to fasely coordinate among threads

concurrent inconsistency issue->synchronization mechanisms

mutual exclusion exclusive access to only one thread at a time

mutex

waiting on other threads -specific condition before proceeding -condition variable

waking up other threads from wait state

creation

thread type:

thread ID, pc, sp, registers, stack, attributes

thread creation:

fork(proc,args) create a thread not unix fork which is to create a new process

new thread created, new thread data will be initialized

notify parent->general: thread is done, return results, status of computation -> application: parent thread -> join

join(thread)

join+id child thread it will be blocked until child thread completed, join will return to the parent the result of the child’s computation. thread data will be freed, terminated.

thread creation example

Thread thread1;
shared_list list;
thread1=fork(safe_insert,4);
safe_insert(6);
join(thread1);

mutexes

override shared list