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.
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 release() or unlock(). If you lock 5 times, then you should call release() 5 times as well before it will be unlocked. However, if you lock 5 times, just one call to unlock() will undo all 5 levels of locking.
Just remember, release() releases one level. But unlock() 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 40 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 | release () |
| releases one recursive lock-level from whoever has the current lock | |
| void | unlock () |
| completely unlocks, regardless of how many times a recursive lock has been obtained | |
| unsigned int | get_lock_level () const |
| returns the lockcount | |
| int | owner () |
| 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 | |
Static Public Attributes | |
| const unsigned int | NO_OWNER = -1U |
| marks as unlocked | |
Protected Member Functions | |
| 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 | |
Constructor & Destructor Documentation
|
|||||||||
|
constructor, just calls the init() function.
Definition at line 45 of file MutexLock.h. |
Member Function Documentation
|
||||||||||||||||
|
Does the work of trying to get a lock.
Pass Definition at line 170 of file MutexLock.h. Referenced by MutexLock< num_doors >::forget(), MutexLock< num_doors >::lock(), and MutexLock< num_doors >::try_lock(). |
|
||||||||||
|
allows you to reset one of the possible owners, so another process can take its place. This is not tested
Definition at line 249 of file MutexLock.h. |
|
|||||||||
|
returns the lockcount
Definition at line 71 of file MutexLock.h. |
|
|||||||||
|
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....
Definition at line 98 of file MutexLock.h. |
|
||||||||||
|
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. This is not a recursive lock - repeated locks still only require one release to undo them.
Definition at line 124 of file MutexLock.h. Referenced by MotionManager::InitAccess(). |
|
||||||||||
|
returns the internal index mapping to the id number supplied by the process
Definition at line 230 of file MutexLock.h. Referenced by MutexLock< num_doors >::forget(), MutexLock< num_doors >::lock(), and MutexLock< num_doors >::try_lock(). |
|
|||||||||
|
returns the current owner's id
Definition at line 74 of file MutexLock.h. Referenced by MutexLock< num_doors >::lock(), and MutexLock< num_doors >::try_lock(). |
|
|||||||||
|
releases one recursive lock-level from whoever has the current lock
Definition at line 150 of file MutexLock.h. Referenced by MutexLock< num_doors >::forget(), and MotionManager::InitAccess(). |
|
|||||||||
|
If you find a way to sleep for a few microseconds instead of busy waiting, put it here.
Definition at line 100 of file MutexLock.h. Referenced by MutexLock< num_doors >::do_try_lock(), and MutexLock< num_doors >::lock(). |
|
||||||||||
|
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. This is not a recursive lock - repeated locks still only require one release to undo them. Definition at line 134 of file MutexLock.h. |
|
|||||||||
|
completely unlocks, regardless of how many times a recursive lock has been obtained
Definition at line 68 of file MutexLock.h. |
Member Data Documentation
|
|||||
|
holds all the doors
Definition at line 115 of file MutexLock.h. Referenced by MutexLock< num_doors >::do_try_lock(), MutexLock< num_doors >::forget(), MutexLock< num_doors >::lookup(), and MutexLock< num_doors >::release(). |
|
|||||
|
counts the number of doors used
Definition at line 116 of file MutexLock.h. |
|
|||||
|
the depth of the lock, 0 when unlocked
Definition at line 118 of file MutexLock.h. Referenced by MutexLock< num_doors >::lock(), MutexLock< num_doors >::release(), and MutexLock< num_doors >::try_lock(). |
|
|||||
|
marks as unlocked
Definition at line 42 of file MutexLock.h. |
|
|||||
|
holds the door index of the current lock owner
Definition at line 117 of file MutexLock.h. Referenced by MutexLock< num_doors >::do_try_lock(), and MutexLock< num_doors >::release(). |
The documentation for this class was generated from the following file:
