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Axel Gray
Axel Gray

POSIX Threads Programming for Beginners and Experts: PDF (46 MB) of the Bestselling Book by David R. Butenhof


Programming with POSIX Threads: A Comprehensive Guide for Developers




Are you a developer who wants to learn how to use POSIX threads in your applications? Do you want to improve the performance, scalability, and reliability of your programs by using multithreading techniques? If so, then this article is for you.




programming with posix threads butenhof pdf 46



In this article, I will introduce you to the book Programming with POSIX Threads by David R. Butenhof, which is one of the best books on the topic of POSIX threads. I will explain what POSIX threads are, why they are useful, and how you can get the book. Then, I will give you an overview of the basic and advanced concepts of POSIX threads, as well as some practical examples that demonstrate how to use them in real-world scenarios. Finally, I will conclude with a summary of the main points, the benefits and challenges of POSIX threads, and some recommendations and resources for further learning.


What are POSIX threads?




POSIX threads, also known as pthreads, are a standard for creating and managing multiple threads of execution within a single process. A thread is a lightweight unit of execution that shares the same address space and resources with other threads in the same process. Threads can run concurrently on multiple processors or cores, or interleaved on a single processor or core.


POSIX threads are defined by the IEEE Standard 1003.1c-1995, which is part of the Portable Operating System Interface (POSIX) specification. POSIX threads are supported by most Unix-like operating systems, such as Linux, macOS, FreeBSD, Solaris, and others. They are also available on some non-Unix platforms, such as Windows, through third-party libraries or wrappers.


Why use POSIX threads?




POSIX threads offer several advantages for developers who want to create multithreaded applications. Some of these advantages are:


  • Performance: By using multiple threads, you can exploit the parallelism of modern hardware and speed up your computations. For example, you can divide a large task into smaller subtasks and assign them to different threads that run simultaneously on different processors or cores. This can reduce the overall execution time and improve the responsiveness of your application.



  • Scalability: By using multiple threads, you can scale your application to handle more workload or users. For example, you can create a thread pool that dynamically allocates and deallocates threads according to the demand. This can increase the throughput and efficiency of your application.



  • Reliability: By using multiple threads, you can isolate faults and errors in your application. For example, you can use separate threads for different components or modules of your application, so that if one thread crashes or hangs, it does not affect the rest of the application. You can also use exception handling and recovery mechanisms to handle errors gracefully.



How to get the book?




If you are interested in learning more about POSIX threads, I highly recommend you to get the book Programming with POSIX Threads by David R. Butenhof. This book is a comprehensive and authoritative guide that covers everything you need to know about POSIX threads. It explains the concepts and principles of multithreading in a clear and concise manner, with plenty of examples and exercises. It also covers the latest features and extensions of POSIX threads, such as thread cancellation, thread-specific data, signals, timers, and more.


You can get the book from various online platforms, such as Amazon, Google Books, or O'Reilly. The book is available in both paperback and ebook formats. The paperback version has 381 pages and costs $46. The ebook version has 448 pages and costs $35.99. You can also download a free PDF version of the book from the author's website: https://www.butenhof.net/programming-with-posix-threads.pdf.


Basic Concepts of POSIX Threads




Now that you have an idea of what POSIX threads are and why they are useful, let's dive into some of the basic concepts of POSIX threads. In this section, I will cover three topics: thread creation and termination, thread synchronization, and thread attributes and scheduling.


Thread creation and termination




The first thing you need to know about POSIX threads is how to create and terminate them. To create a thread, you need to use the function pthread_create, which takes four arguments: a pointer to a thread identifier, a pointer to a thread attribute object, a pointer to a start routine function, and a pointer to an argument for the start routine function. The function returns zero on success, or an error code on failure.


For example, the following code snippet creates a thread that prints "Hello, world!" and then exits:


#include


#include


void *say_hello(void *arg) printf("Hello, world!\n"); return NULL; int main() pthread_t tid; int err; err = pthread_create(&tid, NULL, say_hello, NULL); if (err != 0) perror("pthread_create"); return -1; pthread_exit(NULL);


To terminate a thread, you can use one of the following methods:


  • Return from the start routine: This is the simplest and recommended way to terminate a thread. When a thread returns from its start routine function, it automatically terminates and releases its resources. The return value of the start routine function can be retrieved by another thread using the function pthread_join, which waits for a thread to terminate and returns its exit status.



  • Call pthread_exit: This is another way to terminate a thread explicitly. The function pthread_exit takes one argument: a pointer to an exit status value. The function terminates the calling thread and passes the exit status value to another thread that calls pthread_join. The function does not return.



  • Call pthread_cancel: This is a way to terminate a thread asynchronously by sending it a cancellation request. The function pthread_cancel takes one argument: a thread identifier. The function sends a cancellation request to the specified thread, which may or may not honor it depending on its cancellation state and type. The function returns zero on success, or an error code on failure.



Thread synchronization




The next thing you need to know about POSIX threads is how to synchronize them. Synchronization is the process of coordinating the actions and data access of multiple threads to ensure correctness and consistency. Synchronization is necessary when multiple threads share data or resources that can be modified or accessed concurrently.


POSIX threads provide several mechanisms for synchronization, such as mutexes, condition variables, semaphores, barriers, read-write locks, spin locks, and atomic operations. In this article, I will focus on two of the most commonly used mechanisms: mutexes and condition variables.


A mutex is a mutual exclusion object that allows only one thread at a time to lock it and access a critical section of code or data. A mutex has two states: locked or unlocked. A thread that wants to enter a critical section must first try to lock the mutex using the function pthread_mutex_lock, which blocks until the mutex is available. After finishing the critical section, the thread must unlock the mutex using the function pthread_mutex_unlock, which makes the mutex available for other threads.


For example, the following code snippet uses a mutex to protect a global variable counter that is incremented by multiple threads:


#include


#include


#define NUM_THREADS 10 int counter = 0;


_INITIALIZER; void *increment(void *arg) int i; for (i = 0; i


A condition variable is a synchronization object that allows threads to wait for a certain condition to become true. A condition variable is always associated with a mutex, which protects the shared data that represents the condition. A thread that wants to wait for a condition must first lock the mutex and then call the function pthread_cond_wait, which atomically unlocks the mutex and blocks until another thread signals the condition variable using the function pthread_cond_signal or pthread_cond_broadcast. After being signaled, the thread wakes up and reacquires the mutex before returning from pthread_cond_wait.


For example, the following code snippet uses a condition variable to implement a bounded buffer that can be accessed by multiple producer and consumer threads:


#include


#include


#define BUFFER_SIZE 10 int buffer[BUFFER_SIZE]; int count = 0; int in = 0; int out = 0; pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; pthread_cond_t not_full = PTHREAD_COND_INITIALIZER; pthread_cond_t not_empty = PTHREAD_COND_INITIALIZER; void *producer(void *arg) int i; for (i = 0; i


return 0;


Thread attributes and scheduling




The last thing you need to know about POSIX threads in this section is how to control their attributes and scheduling. Attributes are properties that affect the behavior and performance of threads, such as stack size, detach state, priority, and affinity. Scheduling is the process of allocating CPU time to threads according to their priority and policy.


POSIX threads provide a way to set and get the attributes of threads using thread attribute objects. A thread attribute object is an opaque data structure that stores the attribute values. To create a thread attribute object, you need to use the function pthread_attr_init, which initializes the object with default values. To modify the attribute values, you need to use various functions that start with pthread_attr_set or pthread_attr_get, such as pthread_attr_setstacksize or pthread_attr_getdetachstate. To destroy a thread attribute object, you need to use the function pthread_attr_destroy, which frees the resources associated with the object.


For example, the following code snippet creates a thread attribute object that sets the stack size to 1 MB and the detach state to detached:


#include


#include


#define STACK_SIZE (1024 * 1024) void *do_something(void *arg) // do something return NULL; int main() pthread_t tid; pthread_attr_t attr; int err; err = pthread_attr_init(&attr); if (err != 0) perror("pthread_attr_init"); return -1; err = pthread_attr_setstacksize(&attr, STACK_SIZE); if (err != 0) perror("pthread_attr_setstacksize"); return -1; err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); if (err != 0) perror("pthread_attr_setdetachstate"); return -1; err = pthread_create(&tid, &attr, do_something, NULL); if (err != 0) perror("pthread_create"); return -1; pthread_attr_destroy(&attr); return 0;


POSIX threads also provide a way to set and get the scheduling parameters of threads using thread parameter objects. A thread parameter object is a data structure that stores the scheduling policy and priority of a thread. To set the scheduling parameters of a thread, you need to use the function pthread_setschedparam, which takes three arguments: a thread identifier, a scheduling policy, and a pointer to a thread parameter object. To get the scheduling parameters of a thread, you need to use the function pthread_getschedparam, which takes three arguments: a thread identifier, a pointer to a scheduling policy, and a pointer to a thread parameter object.


For example, the following code snippet sets the scheduling policy of a thread to round-robin and its priority to the maximum value:


#include


#include


void *do_something(void *arg) // do something return NULL; int main() pthread_t tid; struct sched_param param; int policy = SCHED_RR; int max_priority; int err; err = pthread_create(&tid, NULL, do_something, NULL); if (err != 0) perror("pthread_create");


max_priority = sched_get_priority_max(policy); if (max_priority == -1) perror("sched_get_priority_max"); return -1; param.sched_priority = max_priority; err = pthread_setschedparam(tid, policy, &param); if (err != 0) perror("pthread_setschedparam"); return -1; pthread_join(tid, NULL); return 0;


Advanced Topics of POSIX Threads




In this section, I will cover some of the advanced topics of POSIX threads that are not covered in the book Programming with POSIX Threads by David R. Butenhof. These topics are: thread cancellation and cleanup, thread-specific data, and signals and timers.


Thread cancellation and cleanup




As I mentioned earlier, one way to terminate a thread is to call pthread_cancel, which sends a cancellation request to the specified thread. However, the thread may or may not honor the cancellation request depending on its cancellation state and type. The cancellation state can be either enabled or disabled, and the cancellation type can be either deferred or asynchronous.


The cancellation state determines whether a thread can be canceled or not. A thread can set its own cancellation state using the function pthread_setcancelstate, which takes two arguments: a new state and a pointer to the old state. The new state can be either PTHREAD_CANCEL_ENABLE or PTHREAD_CANCEL_DISABLE. The function returns zero on success, or an error code on failure.


The cancellation type determines when a thread can be canceled. A thread can set its own cancellation type using the function pthread_setcanceltype, which takes two arguments: a new type and a pointer to the old type. The new type can be either PTHREAD_CANCEL_DEFERRED or PTHREAD_CANCEL_ASYNCHRONOUS. The function returns zero on success, or an error code on failure.


If a thread has an enabled cancellation state and a deferred cancellation type, it can be canceled only at certain points in its execution, called cancellation points. These are typically functions that block or wait for some event, such as pthread_cond_wait, read, or sleep. If a thread has an enabled cancellation state and an asynchronous cancellation type, it can be canceled at any time.


When a thread is canceled, it may need to perform some cleanup actions before exiting, such as releasing resources, closing files, or notifying other threads. POSIX threads provide a way to register and execute cleanup handlers using the macros pthread_cleanup_push and pthread_cleanup_pop. A cleanup handler is a function that takes one argument: a pointer to some data. The macro pthread_cleanup_push takes two arguments: a pointer to a cleanup handler function and a pointer to its data. The macro pthread_cleanup_pop takes one argument: an execute flag.


The macro pthread_cleanup_push pushes a cleanup handler onto a stack of handlers that are associated with the current thread. The macro pthread_cleanup_pop pops a cleanup handler from the stack and executes it if the execute flag is nonzero. The cleanup handlers are executed in the reverse order of their registration when one of the following events occurs:


  • The thread calls pthread_exit.



  • The thread responds to a cancellation request.



  • The thread returns from its start routine function.



For example, the following code snippet registers a cleanup handler that closes a file descriptor:


#include


#include


#include


void close_fd(void *arg) int fd = *(int *)arg; close(fd); void *do_something(void *arg) int fd; fd = open("some_file", O_RDONLY); if (fd == -1) perror("open"); return NULL; pthread_cleanup_push(close_fd, &fd); // do something with fd pthread_cleanup_pop(1); return NULL; int main() pthread_t tid; int err; err = pthread_create(&tid, NULL, do_something, NULL); if (err != 0) perror("pthread_create"); return -1; pthread_join(tid, NULL); return 0;


Thread-specific data




Another advanced topic of POSIX threads is thread-specific data. Thread-specific data is a mechanism that allows each thread to have its own private data that is not shared with other threads. Thread-specific data can be useful for storing thread-local variables, such as error codes, random seeds, or context information.


POSIX threads provide a way to create and manage thread-specific data using thread key objects. A thread key object is an opaque data structure that identifies a location where thread-specific data can be stored and retrieved. To create a thread key object, you need to use the function pthread_key_create, which takes two arguments: a pointer to a thread key variable and a pointer to a destructor function. The function returns zero on success, or an error code on failure.


The destructor function is a function that takes one argument: a pointer to some thread-specific data. The function is called when a thread that has thread-specific data associated with the key terminates, either normally or by cancellation. The function can be used to free or release the thread-specific data.


To associate thread-specific data with a thread key object, you need to use the function pthread_setspecific, which takes two arguments: a thread key variable and a pointer to some thread-specific data. The function returns zero on success, or an error code on failure.


To retrieve thread-specific data from a thread key object, you need to use the function pthread_getspecific, which takes one argument: a thread key variable. The function returns a pointer to the t


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