Class that acquires, renews, and releases a synchronization token that is serviced in strict FIFO/LIFO ordering and that also supports (1) recursion and (2) readers/writer semantics.
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Classes |
struct | ACE_Token_Queue |
struct | ACE_Token_Queue_Entry |
Public Types |
enum | QUEUEING_STRATEGY { FIFO = -1,
LIFO = 0
} |
Public Member Functions |
| ACE_Token (const ACE_TCHAR *name=0, void *=0) |
| Constructor.
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virtual | ~ACE_Token (void) |
| Destructor.
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int | queueing_strategy (void) |
| Retrieve the current queueing strategy.
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void | queueing_strategy (int queueing_strategy) |
| Set the queueing strategy.
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int | acquire (void(*sleep_hook)(void *), void *arg=0, ACE_Time_Value *timeout=0) |
int | acquire (ACE_Time_Value *timeout=0) |
virtual void | sleep_hook (void) |
int | renew (int requeue_position=0, ACE_Time_Value *timeout=0) |
int | tryacquire (void) |
int | remove (void) |
| Shuts down the ACE_Token instance.
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int | release (void) |
int | acquire_read (void) |
int | acquire_read (void(*sleep_hook)(void *), void *arg=0, ACE_Time_Value *timeout=0) |
int | acquire_write (void) |
| Calls acquire().
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int | acquire_write (void(*sleep_hook)(void *), void *arg=0, ACE_Time_Value *timeout=0) |
| Calls acquire().
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int | tryacquire_read (void) |
| Lower priority try_acquire().
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int | tryacquire_write (void) |
| Just calls <tryacquire>.
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int | tryacquire_write_upgrade (void) |
| Assumes the caller has acquired the token and returns 0.
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int | waiters (void) |
ACE_thread_t | current_owner (void) |
| Return the id of the current thread that owns the token.
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void | dump (void) const |
| Dump the state of an object.
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Public Attributes |
| ACE_ALLOC_HOOK_DECLARE |
| Declare the dynamic allocation hooks.
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Private Types |
enum | ACE_Token_Op_Type { READ_TOKEN = 1,
WRITE_TOKEN
} |
Private Member Functions |
int | shared_acquire (void(*sleep_hook_func)(void *), void *arg, ACE_Time_Value *timeout, ACE_Token_Op_Type op_type) |
| Implements the <acquire> and <tryacquire> methods above.
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void | wakeup_next_waiter (void) |
| Wake next in line for ownership.
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Private Attributes |
ACE_Token_Queue | writers_ |
| A queue of writer threads.
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ACE_Token_Queue | readers_ |
| A queue of reader threads.
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ACE_Thread_Mutex | lock_ |
| ACE_Thread_Mutex used to lock internal data structures.
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ACE_thread_t | owner_ |
| Current owner of the token.
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int | in_use_ |
int | waiters_ |
| Number of waiters.
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int | nesting_level_ |
| Current nesting level.
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ACE_Condition_Attributes | attributes_ |
| The attributes for the condition variables, optimizes lock time.
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int | queueing_strategy_ |
| Queueing strategy, LIFO/FIFO.
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Class that acquires, renews, and releases a synchronization token that is serviced in strict FIFO/LIFO ordering and that also supports (1) recursion and (2) readers/writer semantics.
This class is a more general-purpose synchronization mechanism than many native OS mutexes. For example, it implements "recursive mutex" semantics, where a thread that owns the token can reacquire it without deadlocking. If the same thread calls <acquire> multiple times, however, it must call <release> an equal number of times before the token is actually released. Threads that are blocked awaiting the token are serviced in strict FIFO/LIFO order as other threads release the token (Solaris and Pthread mutexes don't strictly enforce an acquisition order). There are two lists within the class. Write acquires always have higher priority over read acquires. Which means, if you use both write/read operations, care must be taken to avoid starvation on the readers. Notice that the read/write acquire operations do not have the usual semantic of reader/writer locks. Only one reader can acquire the token at a time (which is different from the usual reader/writer locks where several readers can acquire a lock at the same time as long as there is no writer waiting for the lock). We choose the names to (1) borrow the semantic to give writers higher priority and (2) support a common interface for all locking classes in ACE.
An optimized method that efficiently reacquires the token if no other threads are waiting. This is useful for situations where you don't want to degrade the quality of service if there are other threads waiting to get the token. If <requeue_position> == -1 and there are other threads waiting to obtain the token we are queued according to the queueing strategy. If <requeue_position>
-1 then it indicates how many entries to skip over before
inserting our thread into the list of waiters (e.g., <requeue_position> == 0 means "insert at front of the queue"). Renew has the rather odd semantics such that if there are other waiting threads it will give up the token even if the nesting_level_ > 1. I'm not sure if this is really the right thing to do (since it makes it possible for shared data to be changed unexpectedly) so use with caution... This method maintians the original token priority. As in <acquire>, the timeout value is an absolute time.