title: What is thread local storage? Why we need it?
body: <p>I am reading the Threads in OS concepts and i come across "thread local storage (TLS)". What I understood is that the TLS is similar to static or global data, but it is more unique to individual thread. Its bit confusing on what is unique here?</p>
  
  <p>Why can't we pass the data through runner (i.e., thread's actual codes) functions as params to this function?</p>