How to solve the problems, priority inversion and deadlock, of resource sync?
* Critical section pattern
pros: avoid both problems
cons: cost high
* Priority inheritance
pros: avoid priority inversion and simple
cons: deadline and chain blocking could happens
chain blocking: J1 needs S1 and S2 but S1 is used by J2 and S2 by J3. The priority of them is P1>P2>P3. Therefore, J1 must wait for both of them finish.
* Highest locker pattern
One prio ceiling is defined for each resource in system design. The basic idea is that the task owning the resource runs at the highest prio ceiling of all the resources that it currently owns, provided that it is blocking one or more higher prio tasks. In this way, chain blocking is avoided.
pros: avoid chain blocking
cons: deadlock still exists
* Priority ceiling pattern
The idea is to ensure that when a job J preempts the critical section of another job and executes its own critical section, the priority at which this new critical section will execute is guaranteed to be higher than the inherited priorities(so could run) AND the ceiling priorities(so could continue) of all the preempted critical sections in the system. The diff from Highest locker is in the first place the job would not be assigned to the priority ceiling of the locked resource.
pros: avoid both
cons: cost high
Sunday, June 22, 2008
Memory Patterns
* Static allocation pattern
pros: deterministic allocation/deallcation time and no memory fragmentation and easy to maintain.
cons: long init time and large mem supply. inflexible.
* Dynamic allocation pattern
pros: flexible, sizable exec
cons: non-deterministic allocation/deallcation time and mem fragmentation. Hard to maintain ptrs mem.
* Pool allocation pattern
pros: more flexible than static allocation to satisfy dynamic requirements. sub deterministic allocation/deallcation time(possible the pool runs out) and no mem fragmentation.
cons: the num of objs in the pool needs to be explored for the best performance of diff systems.
* Fixed sized buffer pattern
pros: no mem fragmentation since it always uses the worst case of mem requirement.
cons: waste mem on average. And it could be improved by managing varied size heaps.
* Smart ptr pattern
* Garbage collection pattern
* Garbage compactor pattern
pros: deterministic allocation/deallcation time and no memory fragmentation and easy to maintain.
cons: long init time and large mem supply. inflexible.
* Dynamic allocation pattern
pros: flexible, sizable exec
cons: non-deterministic allocation/deallcation time and mem fragmentation. Hard to maintain ptrs mem.
* Pool allocation pattern
pros: more flexible than static allocation to satisfy dynamic requirements. sub deterministic allocation/deallcation time(possible the pool runs out) and no mem fragmentation.
cons: the num of objs in the pool needs to be explored for the best performance of diff systems.
* Fixed sized buffer pattern
pros: no mem fragmentation since it always uses the worst case of mem requirement.
cons: waste mem on average. And it could be improved by managing varied size heaps.
* Smart ptr pattern
* Garbage collection pattern
* Garbage compactor pattern
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