Realizing Concurrency using Posix ThreadsSystem CallSome System Calls For Process Management and File ManagementPipe IPC (Answer to Jason’s Ques)On to threads..IntroductionTopics to be CoveredObjectiveThreadsCreating threadsUsing threadsThread’s local dataThread termination (destruction)Waiting for thread exit01/13/19 1Realizing Concurrency using Posix ThreadsB. Ramamurthy01/13/19 2System Call There are 11 steps in making the system call read (fd, buffer, nbytes)01/13/19 3Some System Calls For Process Management and File Management01/13/19 4•Pipe allows for arbitrary sequences of commands to be coupled together.•Syscall pipe returns two file descriptors: one for writing fd[1] to the pipe and another for reading fd[0] from the pipe. int fd[2], retval;retval = pipe(fd);Pipe IPC (Answer to Jason’s Ques)01/13/19 5On to threads..01/13/19 6Introduction•A thread refers to a thread of control flow: an independent sequence of execution of program code.•Threads are powerful. As with most powerful tools, if they are not used appropriately thread programming may be inefficient.•Thread programming has become viable solution for many problems with the advent of multiprocessors and client-server model of computing.•Typically these problems are expected to handle many requests simultaneously. Example: multi-media, database applications, web applications.01/13/19 7Topics to be Covered•Objective•POSIX threads•What are Threads?•Creating threads•Using threads•Summary01/13/19 8Objective•To study POSIX standard for threads called Pthreads.•To study thread control primitives for creation, termination, join, synchronization, concurrency, and scheduling.•To learn to design multi-threaded applications.01/13/19 9Threads•A thread is a unit of work to a CPU. It is strand of control flow.•A traditional UNIX process has a single thread that has sole possession of the process’s memory and resources.•Threads within a process are scheduled and execute independently.•Many threads may share the same address space.•Each thread has its own private attributes: stack, program counter and register context.01/13/19 10Creating threads•Always include pthread library: #include <pthread.h>•int pthread_create (pthread_t *tp, const pthread_attr_t * attr, void *(* start_routine)(void *), void *arg);•This creates a new thread of control that calls the function start_routine.•It returns a zero if the creation is successful, and thread id in tp (first parameter).•attr is to modify the attributes of the new thread. If it is NULL default attributes are used.•The arg is passing arguments to the thread function.01/13/19 11Using threads1. Declare a variable of type pthread_t2. Define a function to be executed by the thread.3. Create the thread using pthread_createMake sure creation is successful by checking the return value.4. Pass any arguments need through’ arg (packing and unpacking arg list necessary.)5. #include <pthread.h> at the top of your header.6. Compile: g++ -o executable file.cc -lthread01/13/19 12 Thread’s local data•Variables declared within a thread (function) are called local data.•Local (static) data associated with a thread are allocated on the stack. So these may be deallocated when a thread returns. •So don’t plan on using locally declared variables for returning arguments. Plan to pass the arguments thru argument list passed from the caller or initiator of the thread.01/13/19 13Thread termination (destruction)Implicit : Simply returning from the function executed by the thread terminates the thread. In this case thread’s completion status is set to the return value.•Explicit : Use thread_exit. Prototype: void thread_exit(void *status);The single pointer value in status is available to the threads waiting for this thread.01/13/19 14Waiting for thread exit•int pthread_join (pthread_t tid, void * *statusp);•A call to this function makes a thread wait for another thread whose thread id is specified by tid in the above prototype.•When the thread specified by tid exits its completion status is stored and returned in
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