MutexLock< num_doors > Class Template Reference
#include <MutexLock.h>
Inheritance diagram for MutexLock< num_doors >:
Detailed Description
template<unsigned int num_doors>
class MutexLock< num_doors >
A software only mutual exclusion lock. (does not depend on processor or OS support).
Use this to prevent more than one process from accessing a data structure at the same time (which often leads to unpredictable and unexpected results)
The template parameter specifies the maximum number of different processes which need to be protected. This needs to be allocated ahead of time, as there doesn't seem to be a way to dynamically scale as needed without risking possible errors if two processes are both trying to set up at the same time. Also, by using a template parameter, all data structures are contained within the class's memory allocation, so no pointers are involved.
Locks in this class can be recursive or non-recursive, depending whether you call releaseAll() or unlock(). If you lock 5 times, then you need to call unlock() 5 times as well before it will be unlocked. However, if you lock 5 times, just one call to releaseAll() will undo all 5 levels of locking.
Just remember, unlock() releases one level. But releaseAll() completely unlocks.
Note that there is no check that the process doing the unlocking is the one that actually has the lock. Be careful about this.
- Warning:
- Doing mutual exclusion in software is tricky business, be careful about any modifications you make!
"A First Come First Served Mutal Exclusion Algorithm with Small Communication Variables"
Edward A. Lycklama, Vassos Hadzilacos - Aug. 1991
Definition at line 393 of file MutexLock.h.
Public Member Functions | |
| MutexLock () | |
| constructor, just calls the init() function. | |
| void | lock (int id) |
| blocks (by busy looping on do_try_lock()) until a lock is achieved | |
| bool | try_lock (int id) |
| attempts to get a lock, returns true if it succeeds | |
| void | unlock () |
| releases one recursive lock-level from whoever has the current lock | |
| void | releaseAll () |
| completely unlocks, regardless of how many times a recursive lock has been obtained | |
| unsigned int | get_lock_level () const |
| returns the lockcount | |
| int | owner () const |
| returns the current owner's id | |
| void | forget (int id) |
| allows you to reset one of the possible owners, so another process can take its place. This is not tested | |
Protected Member Functions | |
| virtual void | useResource (Resource::Data &) |
| marks the resource as in use | |
| virtual void | releaseResource (Resource::Data &) |
| releases the resource | |
| bool | do_try_lock (unsigned int index, bool block) |
| Does the work of trying to get a lock. | |
| unsigned int | lookup (int id) |
| returns the internal index mapping to the id number supplied by the process | |
| void | init () |
| Doesn't do anything if you have the MUTEX_LOCK_ET_USE_SPINCOUNT undef'ed. Used to do a memset, but that was causing problems.... | |
| void | spin () |
| If you find a way to sleep for a few microseconds instead of busy waiting, put it here. | |
Protected Attributes | |
| door_t | doors [num_doors] |
| holds all the doors | |
| unsigned int | doors_used |
| counts the number of doors used | |
| unsigned int | owner_index |
| holds the door index of the current lock owner | |
| unsigned int | lockcount |
| the depth of the lock, 0 when unlocked | |
Friends | |
| class | MarkScope |
Classes | |
| struct | door_t |
| Holds per process shared info, one of these per process. More... | |
Member Function Documentation
| bool MutexLock< num_doors >::do_try_lock | ( | unsigned int | index, | |
| bool | block | |||
| ) | [protected] |
Does the work of trying to get a lock.
Pass true for block if you want it to use FCFS blocking instead of just returning right away if another process has the lock
Definition at line 577 of file MutexLock.h.
Referenced by MutexLock< num_doors >::forget(), MutexLock< num_doors >::lock(), and MutexLock< num_doors >::try_lock().
| void MutexLock< num_doors >::lock | ( | int | id | ) |
blocks (by busy looping on do_try_lock()) until a lock is achieved
You should pass some process-specific ID number as the input - just make sure no other process will be using the same value.
- Todo:
- I'd like to not use a loop here
Definition at line 496 of file MutexLock.h.
Referenced by MotionManager::func_begin(), WorldStatePool::getCurrentWriteState(), MotionManager::InitAccess(), MotionManager::lock(), and WorldStatePool::WorldStatePool().
| bool MutexLock< num_doors >::try_lock | ( | int | id | ) |
attempts to get a lock, returns true if it succeeds
You should pass some process-specific ID number as the input - just make sure no other process will be using the same value.
Definition at line 517 of file MutexLock.h.
Referenced by MotionManager::trylock().
The documentation for this class was generated from the following file:
