LddConcurrencyAndRaceConditions < Training2

%SECTION0{name=LddConcurrencyAndRaceConditions}% Concurrency and Race Conditions

*Terms*

   * _Concurrency (dt.: Nebenläufigkeit):_ two or more threads run at
     the same time and interact

   * _race condition (dt.: Wettlaufsituation):_ inconsistent results
     due to uncontrolled access to shared data

   * _deadlock (dt.: Blockierung):_ two or more processes are
     indefinetly waiting for each other to free access to a resource

   * _critical path (dt.: kritischer Weg):_ codesegment which accesses
     a shared resource

   * _mutual exclusion (dt. wechselseitiger Ausschluss):_ techniques
     used to protect critical paths against race conditions

*Concurrency in the Linux kernel*

   * in old non-preemptive kernels (before 2.5): 
      * interrupts

   * 2.5 and newer:
      * kernel preemption
      * SMP (other CPU)
      * interrupts
      * delayed code execution (workqueues, tasklets, timers)

*=> we need to protect our critical paths!*
  

*Advice:*

   * lock-free possible?

   * ordering: always obtain multiple locks in the same order (avoids
     deadlocks)

   * start with coarse locking and refine

   * document which functions need to be called with which locks held
5.7.3. The ioctl system call		1. Denx Training Topics		5.7.4.1. Atomic operations
Prev		Home		Next