Pthread Self In C

• ✅ Multithreading: In this programming technique, many threads are enabled within a process to work independently while using the same resources, such as memory space.
• ✅ POSIX Threads (pthreads): These standard threading libraries define a set of C programming language types, functions, and constants.
• ✅ Thread ID (TID): A unique thread ID identifies every thread in a multi-threaded program. The TID is an identifier assigned by the system that distinguishes between different threads within the same process.

History:

POSIX threads were first introduced in the 1980s as a component of the POSIX effort to standardize thread interfaces on UNIX-like operating systems. The pthreads API was specifically crafted to ensure full compatibility across various UNIX platforms, enabling developers to create multi-threaded applications that are portable and can be executed on diverse operating system environments.

Another feature available in the pthreads library is pthread_self, a function that simplifies the process for a thread to retrieve its unique thread ID.

Key Features of POSIX Threads:

There are numerous characteristics of POSIX threads in C. Here are some key attributes of the POSIX threads:

1. Thread Creation:

The library offers functions for generating threads. The main function used for creating threads is pthread_create. This function enables programmers to establish a new thread in a program, defining a specific function for the thread to run.

#include <pthread.h>

int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void     *(*start_routine)(void *), void *arg);

2. Thread Termination:

Threads can be concluded by utilizing the pthread_exit function. This function enables a thread to gracefully exit while passing a value back to the invoking thread.

#include <pthread.h>

void pthread_exit(void *value_ptr);

3. Thread Synchronization:

POSIX threads offer a range of tools for coordinating threads, such as mutexes ( pthreadmutext ), condition variables ( pthreadcondt ), and semaphores ( sem_t ). These synchronization primitives are essential for managing the simultaneous execution of multiple threads and avoiding race conditions.

#include <pthread.h>

int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr);

int pthread_mutex_lock(pthread_mutex_t *mutex);

int pthread_mutex_unlock(pthread_mutex_t *mutex);

int pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr);

int pthread_cond_signal(pthread_cond_t *cond);

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

4. Thread Joining:

The pthread_join method is employed to pause the execution of a thread until it finishes its task. This enables one thread to wait for the completion of another thread.

#include <pthread.h>

int pthread_join(pthread_t thread, void **value_ptr);

5. Thread Attributes:

When initiating a thread, it is possible to define thread attributes such as scheduling policy, stack size, and other properties.

#include <pthread.h>

int pthread_attr_init(pthread_attr_t *attr);

int pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate);

int pthread_attr_setstacksize(pthread_attr_t *attr, size_t stacksize);

6. Thread-Safe Functions:

The POSIX threads library provides numerous thread-safe alternatives to standard C library functions. These secure functions guarantee that they can be invoked concurrently by multiple threads without any conflicts.

#include <stdio.h>

#include <pthread.h>

int pthread_mutex_lock(pthread_mutex_t *mutex);

int pthread_mutex_unlock(pthread_mutex_t *mutex);

FILE *fopen(const char *filename, const char *mode);

Example:

Let's consider a scenario to demonstrate the pthread_self function in the C programming language.

#include <stdio.h>

#include <pthread.h>



void *thread_function(void *arg) {

    pthread_t tid = pthread_self();

    printf("Inside the thread. Thread ID: %lu\n", tid);

    return NULL;

}



int main() {

    pthread_t thread;



    // Create a new thread

    if (pthread_create(&thread, NULL, thread_function, NULL) != 0) {

        fprintf(stderr, "Error creating thread\n");

        return 1;

    }



    // Wait for the thread to finish

    if (pthread_join(thread, NULL) != 0) {

        fprintf(stderr, "Error joining thread\n");

        return 1;

    }



    // In the main thread

    pthread_t main_tid = pthread_self();

    printf("Back in the main thread. Main Thread ID: %lu\n", main_tid);



    return 0;

}

Output:

Inside the thread. Thread ID: 139836372760128

Back in the main thread. Main Thread ID: 139836372764480

Explanation:

1. Include Headers:

• ✅ #include <stdio.h>: It includes the standard input/output library for functions like printf .
• ✅ #include <pthread.h>: It includes the POSIX threads library for multithreading functionalities.

1. Thread Function (thread_function):

• ✅ This function is executed by the newly created thread.
• ✅ pthreadt tid = pthreadself;: It retrieves the thread ID of the current thread using pthread_self and stores it in the variable tid.
• ✅ printf("Inside the thread. Thread ID: %lu\n", tid);: It prints the thread ID to the console.

1. Main Function:

• ✅ pthreadt thread;: It declares a variable thread of type pthreadt to store the thread ID of the newly created thread.
• ✅ pthreadcreate(&thread, NULL, threadfunction, NULL): It creates a new thread using pthreadcreate . The new thread will execute the threadfunction . The thread ID is stored in the variable thread.
• ✅ pthread_join(thread, NULL): It waits for the newly created thread to finish its execution. It ensures that the main thread doesn't proceed until the new thread has been completed.
• ✅ pthreadt maintid = pthreadself;: It retrieves the thread ID of the main thread using pthreadself and stores it in the variable main_tid.
• ✅ printf("Back in the main thread. Main Thread ID: %lu\n", main_tid);: It prints the thread ID of the main thread to the console.
• ✅ return 0;: It indicates successful program execution.

1. Compilation:

• ✅ The program should be compiled with the appropriate thread library flags, such as -lpthread for GCC, to link the pthread library.

1. Execution:

• ✅ When the program is executed, it will create a new thread, print its thread ID, wait for it to finish, and then print the thread ID of the main thread.

Time and Space Complexities:

Time Complexity:

• ✅ The operation inside the thread_funtion and the main function dominate the time complexity.
• ✅ The primary operations involve creating a thread ('pthreadcreate') and waiting for the thread to finish ('pthreadjoin') .
• ✅ These two operations generally have a time complexity of constant complexity O(1) because neither operation time increases with the size of the input.
• ✅ Therefore, the overall time complexity of the provided code is O(1) .

Space Complexity:

• ✅ The primary space usage is related to the thread creation and the storage of thread IDs.
• ✅ The 'pthreadt' variables ( 'thread' and 'maintid' ) and the 'int' variable ( 'thread_ids' ) are used to store thread IDs.
• ✅ The space required for these variables is constant and does not depend on the size of the input.
• ✅ Therefore, the overall space complexity of the provided code is also O(1) .

Example 2:

Let's consider a different instance to demonstrate the pthread_self function in the C programming language.

#include <stdio.h>

#include <pthread.h>



#define NUM_THREADS 3



// Function to be executed by the threads

void *thread_function(void *arg) {

    int thread_id = *(int *)arg;

    

    // Print the thread ID and perform some task

    printf("Thread %d: Hello from the thread!\n", thread_id);



    // Return from the thread

    return NULL;

}



int main() {

    pthread_t threads[NUM_THREADS];  // Array to store thread IDs

    int thread_ids[NUM_THREADS];     // Array to store unique IDs for each thread



    // Create multiple threads

    for (int i = 0; i < NUM_THREADS; ++i) {

        thread_ids[i] = i;

        if (pthread_create(&threads[i], NULL, thread_function, &thread_ids[i]) != 0) {

            fprintf(stderr, "Error creating thread %d\n", i);

            return 1;

        }

    }



    // Wait for all threads to finish

    for (int i = 0; i < NUM_THREADS; ++i) {

        if (pthread_join(threads[i], NULL) != 0) {

            fprintf(stderr, "Error joining thread %d\n", i);

            return 1;

        }

    }



    // In the main thread

    printf("Back in the main thread.\n");



    return 0;

}

Output:

Thread 0: Hello from the thread!

Thread 1: Hello from the thread!

Thread 2: Hello from the thread!

Back in the main thread.

Explanation:

1. Thread Function (thread_function):

• ✅ The thread_function is the function that will be executed by each thread. It takes a single argument void *arg , which is expected to be a pointer to an integer representing the unique ID of the thread.
• ✅ Inside the function, the argument is cast to an integer (int thread_id = (int )arg;) , representing the thread's unique identifier.
• ✅ The thread prints a message to the console, including its unique ID, indicating that it has started.
• ✅ After that, the thread returns (return NULL;) , indicating the completion of its task.

1. Main Function:

• ✅ #define NUM_THREADS 3: A preprocessor directive to define the number of threads as 3.
• ✅ pthreadt threads[NUMTHREADS];: An array to store the thread IDs of the created threads.
• ✅ int threadids[NUMTHREADS];: An array to store unique IDs for each thread.

1. Creating Threads:

• ✅ A loop (for (int i = 0; i < NUM_THREADS; ++i)) is used to create multiple threads.
• ✅ thread_ids[i] = i;: It assigns a unique ID to each thread.
• ✅ pthreadcreate(&threads[i], NULL, threadfunction, &threadids[i]): It creates a new thread using pthreadcreate. The thread will execute thread_function with the unique ID passed as an argument.
• ✅ If an error occurs during thread creation, an error message is printed to the standard error stream (stderr), and the program exits with an error code.

1. Waiting for Threads to Finish:

• ✅ Another loop is used to wait for all threads to finish.
• ✅ pthread_join(threads[i], NULL): It waits for the thread with ID threads[i] to finish its execution. If an error occurs during thread joining, an error message is printed to stderr , and the program exits with an error code.

1. Main Thread:

• ✅ After all threads have finished, the main thread prints a message indicating that it is back in the main thread.

1. Compilation and Execution:

• ✅ The code needs to be compiled with the appropriate thread library flags, such as -lpthread for GCC :
• ✅ gcc -o multithreadexample multithreadexample.c -lpthread
• ✅ After compilation, run the executable:
• ✅ ./multithread_example

Time and Space Complexity:

1. Time Complexity:

• ✅ Thread Creation (pthread_create):
• ✅ The loop that creates multiple threads runs NUMTHREADS times, so the overall time complexity for thread creation is O(NUMTHREADS) .
• ✅ The overall time complexity is O(NUM_THREADS) .

1. Space Complexity:

• ✅ The space required for storing thread IDs is proportional to the number of threads (NUMTHREADS). Therefore, the space complexity of these arrays is O(NUMTHREADS).
• ✅ The overall space complexity is O(NUM_THREADS).

Advantages of pthread_self:

There are several advantages of the pthread_self function in C. Some main advantages are as follows:

• ✅ Portability: Using a standardized API, users can develop on different Unix-like systems multi-threaded services that are shared by all compliant systems. In the new scheme, every piece of code may involve multiple threads that can cooperate even if they are deployed on different platforms.
• ✅ Parallelism and Concurrency: Pthreads allow developers to create multiple tasks within one process. As the hardware executes these tasks simultaneously, this concurrent execution mode boosts performance on multicore systems.
• ✅ Scalability: Pthreads multi-threading allows applications to scale as hardware resources change. Therefore, tasks in programs can be divided into multiple threads and then run on different processors or cores. Certain types of programs run faster when it is done, giving them better performance in general.
• ✅ Flexible Thread Creation: With Pthreads, developers can design their own thread creation routine to meet their needs. For example, when a developer creates a thread, he can set the stack size, scheduling policy, and thread priority. It helps fine-tune specific application requirements.
• ✅ Thread-Safe Functions: Pthreads also provides thread-safe versions of many standard C library functions. A function is said to be "thread-safe" in these circumstances since it protects against data corruption or deadlock, among others. Multiple threads share common resources and use these types of functions without any problems.

Applications of pthread_self:

There are several applications of the pthread_self function in C. Some main applications are as follows:

• ✅ Servers: Server applications such as web, database servers and the like often use threads (pthreads) to enable multiple client requests to be handled concurrently. Therefore, each incoming connection can be treated as a separate thread, allowing a single server to service more than one client at any given moment.
• ✅ Multiprocess File Systems: Pthreads making it possible for multiple users or processes to access their files at once can significantly improve the efficiency of file I/O operations. In contrast with distributed file systems and file servers, there are many file systems supporting this basic function.
• ✅ Network Programming: Threads can provide a solution for network applications like chat servers, messaging systems, and peer-to-peer applications to manage multiple network connections simultaneously.
• ✅ Simulation and Gaming: Pthreads are often used in simulation software and video games. In these programs, physics simulations, AI processing and rendering, and interpolation, among others, run in parallel, which enhances the realism and responsiveness of the simulations or games for human beings.
• ✅ Data Analysis and Machine Learning: Pthreads should be found helpful for some kinds of problems, where large amounts of data can be processed cooperatively. Examples could be machine-learning algorithms that use numerical optimization techniques and statistical processing or data-analysis programs working on big databases. It is especially useful for tasks to be executed as independent sub-problems.

Disadvantages of pthread_self:

There are several disadvantages of the pthread_self function in C. Some main disadvantages are as follows:

• ✅ Platform Dependency: This is a result of the way systems support these features with different levels of help and how various POSIX standards are complied with on different Operating Systems, meaning all the subtleties are hard to spot and platform specific.
• ✅ Complexity and error risk: Concurrent programming introduces complexity into the logical flow of the program, in particular when dealing with shared resources. Deadlocks and race conditions should be avoided by using such a synchronization mechanism correctly as mutual exclusion (mutexes) and conditional variables. Finally, misuse of these constructs accelerates difficult-to-find bugs.
• ✅ Lack of native windows support: Pthreads is mainly developed for UNIX like systems. Thus, there is no support for it on Windows. While there are other third-party implementations in Windows of pthreads but they don't have portability.
• ✅ Some abstraction limitations: The thread model provided by Pthreads is relatively low-level. On the other hand, developers must handle many of these aspects, like creation and termination of threads. This results in extra code (also known as 'boilerplate code instance') unlike higher-level threading models found in some other languages.

Conclusion:

In summary, Utilizing POSIX Threads (pthreads) for developing multithreaded applications on Unix-like operating systems has become a well-established and popular approach. This threading library offers numerous benefits, including parallelism, adaptability, and versatility, which are not as readily available in RPC-driven systems. By leveraging pthreads, it becomes feasible to run multiple tasks simultaneously within a single process, optimizing the use of multicore architectures.

When considering broadly, POSIX Threads remain a crucial tool for concurrent programming in the C language. They offer a balance between control and abstraction for developers operating on systems that support POSIX. By using these resources judiciously, users can significantly improve the performance of software and systems. This makes them invaluable for a wide range of applications, from server-side software to scientific computations.