9)Threads , Hyper-threading , fork() and exec() System call

Thread = basic unit of CPU utilization , Thread ID + PC(program counter) + register set + stack

in multi thread  = code ,date ,file are shared but they have their own register and stack.

 

benefits

Responsiveness = muti thread operate simultaneously even if one thread takes long time or get blocked , user can still interact with other theads that is working fine.

Resource sharing = allows an application to have several different threads of activity within the same address space.

Economy = context-switch threads is much more eiffcient than context-switch process. since they are sharing resources.

Utilzation of mutiprocessor architectures = with mutiple CPU core and muti thread process wil run concurrently using mutiple core for each thread.

 

Types of Threads:

User Threads - Supproted above the kerenl and are managed without kernel support

Kernel Threads - Supported and managed directly by the operating system

 

User threads and Kernel threads Relationship

many to one model

• maps many user thread to one kerenl thread.
• able to manage thread in user space which is efficient.
• entire proces get block if a thread makes a blocking system call = kernel thread will be blocked therefore other threads will get block
• since only one thread can access the kernel at a time, mutiple threads are unable to run in parallel on mutiprocessors.

 

one to one model

• even if one thread makes blocking system call entire process won't get block.
• allows mutiple threads to run in parallel on muti processors.
• creating one user thread require one kerenl thread = costly
• having many kernel thread is heavy. also system will restrict the number of kernel thread that it can handle.

 

many to many model

• many user threads will map to equal or smaller number of kernel threads.
• developer can create many user thread and it will run parallel in muti processor system.
• even with blocking system call , the kernel can schedule another thread for execution.

 

Hyper-threading , Simultaneous Muti-threading (SMT)

many of muti-thread process are exisiting. 

physical number of core process they are divided into mutiple logical processor 

it enables the processor to execute 2 threads or sets of instructions , at the same time. since hyper-threading allows 2 streams to be executed in parallel , it's like having 2 seperate processors working together.

 

 

fork()

system call , to create a separate , duplicate process but process ID will be different. 

5837 is the parent process ID and 5838 is the forked process ID.

 

exec()

system call , the program specified in the parameter to exec() will replace the entire process , including all threads.

it is like recursive call as soon as execv was called , it jumped to ex2 program and execute and then did not came back to ex1.

notice Process ID are same. which means Process 's contents are replaced it is not created.