Operative system does not recognized user's thread why with examples ?

The operating system does not recognize a user's thread because it is not aware of the threads created by user-level programs. User-level threads are managed by the program itself and do not require intervention from the operating system.

Here are a few examples to illustrate this:

1. Java threads: In Java, the Thread class allows users to create and manage threads within their programs. These threads are not recognized by the operating system as they are managed by the Java Virtual Machine (JVM) at the user level.

2. Python threads: Python provides a threading module that allows users to create and manage threads. Similar to Java, these threads are managed by the Python interpreter and are not recognized by the operating system.

3. User-level thread libraries: Some programming languages or libraries provide their own thread management mechanisms at the user level. For example, the POSIX Threads (pthreads) library in C/C++ allows users to create and manage threads without involving the operating system. These threads are not visible to the operating system.

In all these cases, the operating system is not aware of the existence of user-level threads. It only sees the main thread of the program and does not provide any scheduling or resource management for user-level threads.