Pthreads Error Codes
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API Compiling Threaded Programs Thread Management Creating and Terminating Threads Passing Arguments to Threads Joining and Detaching how to find pthread_threads_max Threads Stack Management Miscellaneous Routines Exercise 1 Mutex Variables Mutex pthread example Variables Overview Creating and Destroying Mutexes Locking and Unlocking Mutexes Condition Variables Condition Variables pthread c++ Overview Creating and Destroying Condition Variables Waiting and Signaling on Condition Variables Monitoring, Debugging and Performance Analysis Tools for Pthreads LLNL Specific Information pthread functions and Recommendations Topics Not Covered Exercise 2 References and More Information Appendix A: Pthread Library Routines Reference Abstract In shared memory multiprocessor architectures, threads can be used to implement parallelism. Historically, hardware vendors have implemented their own proprietary versions of threads, making portability a concern for software
Pthread Api
developers. For UNIX systems, a standardized C language threads programming interface has been specified by the IEEE POSIX 1003.1c standard. Implementations that adhere to this standard are referred to as POSIX threads, or Pthreads. The tutorial begins with an introduction to concepts, motivations, and design considerations for using Pthreads. Each of the three major classes of routines in the Pthreads API are then covered: Thread Management, Mutex Variables, and Condition Variables. Example codes are used throughout to demonstrate how to use most of the Pthreads routines needed by a new Pthreads programmer. The tutorial concludes with a discussion of LLNL specifics and how to mix MPI with pthreads. A lab exercise, with numerous example codes (C Language) is also included. Level/Prerequisites: This tutorial is ideal for those who are new to parallel programming with pthreads. A basic understanding of parall
to the Single Unix Specification standard consisted to submit an example of use for pthread_sigmask()[1]. Since my proposal was going to be viewed by many Austin Group's contributors (some being "recognized UNIX authority"),
Pthread Error Codes To String
I tried to make my example as perfect as possible. In an pthread mutex example academic fashion, I checked every function's return code for possible errors. That's where I got it wrong for the pthread error handling Pthreads APIs. Oh well, they do not use errno… The Problem: Before the advent of Pthreads, POSIX functions used to return -1 on error, and set the corresponding error code in https://computing.llnl.gov/tutorials/pthreads/ the global variable errno[2]. This mechanism has a few drawbacks even for single-threaded process: it is not simple to return -1 as valid value. a signal handler may change the errno value between the point a function set errno, and the point where you check the errno variable. Of course, a global errno doesn't work for multi-threaded processes. Indeed, a thread could execute http://www.domaigne.com/blog/computing/pthreads-errors-and-errno/ a function that modifies errno just before you check the value in another thread. The (Pthreads) Solution: Since Pthreads, the errno variable is thread-local. That is, every thread has its own "errno copy". If you (or a system function) set the errno variable in one thread, it won't affect the errno value in any other thread. This is shown in the example below. Download errno_01.c1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 /*------------------------------ errno_01.c -------------------------------* compile with: cc -pthread errno_01.c -o errno_01 Copyright Loic Domaigne. Licensed under the Apache License, Version 2.0. *--------------------------------------------------------------------------*/ #include
set of interfaces (functions, header files) for threaded programming commonly known as POSIX threads, or Pthreads. A single process can contain multiple threads, all of which are executing the same program. These threads share the same http://man7.org/linux/man-pages/man7/pthreads.7.html global memory (data and heap segments), but each thread has its own stack (automatic variables). POSIX.1 also requires that threads share a range of other attributes (i.e., these attributes are process-wide rather than per-thread): - process ID https://kripken.github.io/emscripten-site/docs/porting/pthreads.html - parent process ID - process group ID and session ID - controlling terminal - user and group IDs - open file descriptors - record locks (see fcntl(2)) - signal dispositions - file mode creation mask (umask(2)) - error codes current directory (chdir(2)) and root directory (chroot(2)) - interval timers (setitimer(2)) and POSIX timers (timer_create(2)) - nice value (setpriority(2)) - resource limits (setrlimit(2)) - measurements of the consumption of CPU time (times(2)) and resources (getrusage(2)) As well as the stack, POSIX.1 specifies that various other attributes are distinct for each thread, including: - thread ID (the pthread_t data type) - signal mask (pthread_sigmask(3)) - the errno variable - alternate signal stack (sigaltstack(2)) - real-time scheduling pthreads error codes policy and priority (sched(7)) The following Linux-specific features are also per-thread: - capabilities (see capabilities(7)) - CPU affinity (sched_setaffinity(2)) Pthreads function return values Most pthreads functions return 0 on success, and an error number on failure. Note that the pthreads functions do not set errno. For each of the pthreads functions that can return an error, POSIX.1-2001 specifies that the function can never fail with the error EINTR. Thread IDs Each of the threads in a process has a unique thread identifier (stored in the type pthread_t). This identifier is returned to the caller of pthread_create(3), and a thread can obtain its own thread identifier using pthread_self(3). Thread IDs are guaranteed to be unique only within a process. (In all pthreads functions that accept a thread ID as an argument, that ID by definition refers to a thread in the same process as the caller.) The system may reuse a thread ID after a terminated thread has been joined, or a detached thread has terminated. POSIX says: "If an application attempts to use a thread ID whose lifetime has ended, the behavior is undefined." Thread-safe functions A thread-safe function is one that can be safely (i.e., it will deliver the same results regardless of whether it is) called from multiple threads at the same time. POSIX.1-2001 and POSIX.1-2008 require that all functions speci
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