UppsalaUniversity
     ThreadprogrammingwithPOSIXThreads
                  (Pthreads)
                  Karl Ljungkvist
                                UppsalaUniversity
  Whatarethreads?
      Definition:
        ◮ Independentstreamsofinstructions within a single
           program,whichcanbescheduledindependentlyby
           the OS
      In practice:
        ◮ Athreadisaprocedure/functionrunning
           independently from the main program.
        ◮ Awayofutilizing multiple cores.
      Lightweight process:
        ◮ Only duplicates a necessary minimal
        ◮ Mostresources are shared within the process
        ◮ Less overhead
  Karl Ljungkvist | karl.ljungkvist@it.uu.se                          | 2/45
                                UppsalaUniversity
  Processes vs Threads
    Processes:                         Threads:
      ◮ Multiple instances of the        ◮ Single program with
         sameprogram,which                 parallel internal threads
         cancommunicateby                  sharing resources
         messagepassing                    (memory,openfiles,etc)
            Core 0 a.out                               a.out
                                              Core 0    t0
            Core 1 a.out                      Core 1    t1
            Core 2 a.out                      Core 2    t2
            Core 3 a.out                      Core 3    t3
  Karl Ljungkvist | karl.ljungkvist@it.uu.se                          | 3/45
                                        UppsalaUniversity
   Sharedresources
     Athreadcontainsprivate                      In addition, a Unix process
        ◮ Programcounter                         also has
        ◮ Registers and stack pointer               ◮ Process, process group, user, and
        ◮ Schedulingproperties (i.e. policy            groupIDs
           andpriority)                             ◮ Environment
        ◮ Setofpendingandblocked                    ◮ Workingdirectory
           signals                                  ◮ Programinstructions
                                                    ◮ StackandHeap
                                                    ◮ File descriptors
                                                    ◮ Signal actions
                                                    ◮ Sharedlibraries
                                                    ◮ Inter-process communication
        Lightweight process                            tools
          ◮ Process to thread creation overhead ∼ 10:1
   Karl Ljungkvist | karl.ljungkvist@it.uu.se                                            | 4/45