Operating System : Threads (part 2)

💠 Different types of threads :

• User threads : also known as user-level threads or application threads , they are managed entierly by the application or user-level libraries , rather than the operating system’s kernel. these threads are created, scheduled and managed by the application itself without direct involvement from the OS.

» user threads provide level of abstraction and flexibility to the application.

» they are not visible to the OS ( handeled within the application’s address space).

» they do not take advantage of features like parallel execution on multiple processors.

» The threads you create using the language’s thread APIs (e.g., Java’s Thread class or Python’s threading module) are typically user threads.

• Kernel threads ( thread Noyau ) : also referred to as system threads or kernel-level threads, they are managed directly by the OS’s kernel , also supported and scheduled by the kernel. this allows them to take advantage of the parallel execution on multiple processors and utilize kernel-level ressources efficiently.

» they are Visible to the OS .

» The kernel manages the scheduling, synchronization, and resource allocation for these threads.

» they are typically created using system calls provided by the OS
( the threads created using system calls such as pthread_create or CreateThread are kernel threads. ) .

» These threads are scheduled and managed by the operating system kernel and can run in parallel on multiple processors.

💠Thread POSIX ( pthread.h library ) :

🔸One of the key operations is creating a thread. To create a thread, we use the pthread_createfunction, which has the following syntax:

int pthread_create (pthread_t *tid , const pthread_attr_t *tattr, void * (*start_routine)(void *), void *arg);

🔸Let’s break down the parameters of pthread_create :

1. pthread_t *tid: This is a pointer to a variable of type pthread_t, which will hold the unique identifier of the created thread. This identifier can be used for further thread operations.
2. const pthread_attr_t *tattr: This parameter allows you to specify attributes for the thread, such as stack size or scheduling priority. You can pass NULL if you want to use the default attributes.
3. void *(*start_routine)(void *): This is a function pointer to the routine that will be executed by the newly created thread. The routine should take a void* argument and return a void* value. This function will be the entry point of the thread.
4. void *arg: This is the argument that you can pass to the start_routine function. It can be any data or NULL if no argument is needed.

🔸 The pthread_create function returns an integer value. If the call is successful, it returns 0, indicating that the thread was created successfully. Otherwise, it returns a non-zero value, which represents an error identifier.

Here are some scenarios involving threads along with their corresponding code snippets in C using POSIX threads (pthread.h). These examples cover different use cases and thread-related operations:

🔰💠✅☑️🔸🔹🔺🔻🔷

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