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# ACE_Message_Queue<> Class Template Reference

A threaded message queueing facility, modeled after the queueing facilities in System V STREAMs. More...

`#include <Message_Queue_T.h>`

Inheritance diagram for ACE_Message_Queue<>:

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Collaboration diagram for ACE_Message_Queue<>:

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List of all members.

## Public Types

typedef ACE_Message_Queue_Iterator< ACE_SYNCH_USE > | ITERATOR
typedef ACE_Message_Queue_Reverse_Iterator< ACE_SYNCH_USE > | REVERSE_ITERATOR

## Public Methods

| ACE_Message_Queue (size_t high_water_mark=ACE_Message_Queue_Base::DEFAULT_HWM, size_t low_water_mark=ACE_Message_Queue_Base::DEFAULT_LWM, ACE_Notification_Strategy *=0)
virtual int | open (size_t hwm=ACE_Message_Queue_Base::DEFAULT_HWM, size_t lwm=ACE_Message_Queue_Base::DEFAULT_LWM, ACE_Notification_Strategy *=0)
virtual int | close (void)
virtual | ~ACE_Message_Queue (void)
| Release all resources from the message queue and mark it as deactivated.
virtual int | flush (void)
virtual int | flush_i (void)
virtual int | peek_dequeue_head (ACE_Message_Block *&first_item, ACE_Time_Value *timeout=0)
virtual int | enqueue_prio (ACE_Message_Block *new_item, ACE_Time_Value *timeout=0)
virtual int | enqueue_deadline (ACE_Message_Block *new_item, ACE_Time_Value *timeout=0)
virtual int | enqueue (ACE_Message_Block *new_item, ACE_Time_Value *timeout=0)
virtual int | enqueue_tail (ACE_Message_Block *new_item, ACE_Time_Value *timeout=0)
virtual int | enqueue_head (ACE_Message_Block *new_item, ACE_Time_Value *timeout=0)
virtual int | dequeue (ACE_Message_Block *&first_item, ACE_Time_Value *timeout=0)
| This method is an alias for the following <dequeue_head> method.
virtual int | dequeue_head (ACE_Message_Block *&first_item, ACE_Time_Value *timeout=0)
virtual int | dequeue_prio (ACE_Message_Block *&first_item, ACE_Time_Value *timeout=0)
virtual int | dequeue_tail (ACE_Message_Block *&dequeued, ACE_Time_Value *timeout=0)
virtual int | dequeue_deadline (ACE_Message_Block *&dequeued, ACE_Time_Value *timeout=0)
virtual int | is_full (void)
| True if queue is full, else false.
virtual int | is_empty (void)
| True if queue is empty, else false.
virtual size_t | message_bytes (void)
virtual size_t | message_length (void)
virtual int | message_count (void)
virtual void | message_bytes (size_t new_size)
virtual void | message_length (size_t new_length)
virtual size_t | high_water_mark (void)
virtual void | high_water_mark (size_t hwm)
virtual size_t | low_water_mark (void)
virtual void | low_water_mark (size_t lwm)
virtual int | deactivate (void)
virtual int | activate (void)
virtual int | pulse (void)
virtual int | state (void)
virtual int | deactivated (void)
virtual int | notify (void)
virtual ACE_Notification_Strategy * | notification_strategy (void)
| Get the notification strategy for the <Message_Queue>.
virtual void | notification_strategy (ACE_Notification_Strategy *s)
| Set the notification strategy for the <Message_Queue>.
virtual ACE_SYNCH_MUTEX_T & | lock (void)
| Returns a reference to the lock used by the <ACE_Message_Queue>.
virtual void | dump (void) const
| Dump the state of an object.

## Public Attributes

| ACE_ALLOC_HOOK_DECLARE
| Declare the dynamic allocation hooks.

## Protected Methods

virtual int | enqueue_i (ACE_Message_Block *new_item)
| Enqueue an <ACE_Message_Block *> in accordance with its priority.
virtual int | enqueue_deadline_i (ACE_Message_Block *new_item)
| Enqueue an <ACE_Message_Block *> in accordance with its deadline time.
virtual int | enqueue_tail_i (ACE_Message_Block *new_item)
| Enqueue an <ACE_Message_Block *> at the end of the queue.
virtual int | enqueue_head_i (ACE_Message_Block *new_item)
| Enqueue an <ACE_Message_Block *> at the head of the queue.
virtual int | dequeue_head_i (ACE_Message_Block *&first_item)
virtual int | dequeue_prio_i (ACE_Message_Block *&dequeued)
virtual int | dequeue_tail_i (ACE_Message_Block *&first_item)
virtual int | dequeue_deadline_i (ACE_Message_Block *&first_item)
virtual int | is_full_i (void)
| True if queue is full, else false.
virtual int | is_empty_i (void)
| True if queue is empty, else false.
virtual int | deactivate_i (int pulse=0)
virtual int | activate_i (void)
| Activate the queue.
virtual int | wait_not_full_cond (ACE_Guard< ACE_SYNCH_MUTEX_T > &mon, ACE_Time_Value *timeout)
| Wait for the queue to become non-full.
virtual int | wait_not_empty_cond (ACE_Guard< ACE_SYNCH_MUTEX_T > &mon, ACE_Time_Value *timeout)
| Wait for the queue to become non-empty.
virtual int | signal_enqueue_waiters (void)
| Inform any threads waiting to enqueue that they can procede.
virtual int | signal_dequeue_waiters (void)
| Inform any threads waiting to dequeue that they can procede.

## Protected Attributes

ACE_Message_Block * | head_
| Pointer to head of ACE_Message_Block list.
ACE_Message_Block * | tail_
| Pointer to tail of ACE_Message_Block list.
size_t | low_water_mark_
| Lowest number before unblocking occurs.
size_t | high_water_mark_
| Greatest number of bytes before blocking.
size_t | cur_bytes_
| Current number of bytes in the queue.
size_t | cur_length_
| Current length of messages in the queue.
int | cur_count_
| Current number of messages in the queue.
ACE_Notification_Strategy * | notification_strategy_
| The notification strategy used when a new message is enqueued.
ACE_SYNCH_MUTEX_T | lock_
| Protect queue from concurrent access.
ACE_SYNCH_CONDITION_T | not_empty_cond_
| Used to make threads sleep until the queue is no longer empty.
ACE_SYNCH_CONDITION_T | not_full_cond_
| Used to make threads sleep until the queue is no longer full.

## Private Methods

void | operator= (const ACE_Message_Queue< _ACE_SYNCH > &)
| ACE_Message_Queue (const ACE_Message_Queue< _ACE_SYNCH > &)

## Friends

class | ACE_Message_Queue_Iterator< ACE_SYNCH_USE >
class | ACE_Message_Queue_Reverse_Iterator< ACE_SYNCH_USE >

## Detailed Description

### template<ACE_SYNCH_DECL>
class ACE_Message_Queue<>

A threaded message queueing facility, modeled after the queueing facilities in System V STREAMs.

An <ACE_Message_Queue> is the central queueing facility for messages in the ACE framework. If <ACE_SYNCH_DECL> is <ACE_MT_SYNCH> then all operations are thread-safe. Otherwise, if it's <ACE_NULL_SYNCH> then there's no locking overhead.

## Member Typedef Documentation

template<ACE_SYNCH_DECL >
typedef ACE_Message_Queue_Iterator<ACE_SYNCH_USE> ACE_Message_Queue<>::ITERATOR

template<ACE_SYNCH_DECL >
typedef ACE_Message_Queue_Reverse_Iterator<ACE_SYNCH_USE> ACE_Message_Queue<>::REVERSE_ITERATOR

## Constructor & Destructor Documentation

template<ACE_SYNCH_DECL >
ACE_Message_Queue<>::ACE_Message_Queue | ( | size_t | high_water_mark = ACE_Message_Queue_Base::DEFAULT_HWM,
|  | size_t | low_water_mark = ACE_Message_Queue_Base::DEFAULT_LWM,
|  | ACE_Notification_Strategy * | = 0
| ) |

Initialize an <ACE_Message_Queue>. The <high_water_mark> determines how many bytes can be stored in a queue before it's considered "full." Supplier threads must block until the queue is no longer full. The <low_water_mark> determines how many bytes must be in the queue before supplier threads are allowed to enqueue additional <ACE_Message_Block>s. By default, the <high_water_mark> equals the <low_water_mark>, which means that suppliers will be able to enqueue new messages as soon as a consumer removes any message from the queue. Making the <low_water_mark> smaller than the <high_water_mark> forces consumers to drain more messages from the queue before suppliers can enqueue new messages, which can minimize the "silly window syndrome."

template<ACE_SYNCH_DECL >
virtual ACE_Message_Queue<>::~ACE_Message_Queue | ( | void |  | ) | `[virtual]`

| Release all resources from the message queue and mark it as deactivated.

template<ACE_SYNCH_DECL >
ACE_Message_Queue<>::ACE_Message_Queue | ( | const ACE_Message_Queue< _ACE_SYNCH > & |  | ) | `[private]`

## Member Function Documentation

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::activate | ( | void |  | ) | `[virtual]`

| Reactivate the queue so that threads can enqueue and dequeue messages again. Returns the state of the queue before the call. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::activate_i | ( | void |  | ) | `[protected, virtual]`

| Activate the queue.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::close | ( | void |  | ) | `[virtual]`

| Release all resources from the message queue and mark it as deactivated. Returns the number of messages released from the queue. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::deactivate | ( | void |  | ) | `[virtual]`

| Deactivate the queue and wakeup all threads waiting on the queue so they can continue. No messages are removed from the queue, however. Any other operations called until the queue is activated again will immediately return -1 with <errno> == ESHUTDOWN. Returns WAS_INACTIVE if queue was inactive before the call and WAS_ACTIVE if queue was active before the call. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::deactivate_i | ( | int | pulse = 0 | ) | `[protected, virtual]`

Notifies all waiting threads that the queue has been deactivated so they can wakeup and continue other processing. No messages are removed from the queue.

Parameters:

  pulse | If 0, the queue's state is changed to DEACTIVATED and any other operations called until the queue is reactivated will immediately return -1 with errno == ESHUTDOWN. If not zero, only the waiting threads are notified and the queue's state changes to PULSED.

Returns:
  The state of the queue before the call.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::deactivated | ( | void |  | ) | `[virtual]`

| Returns true if the state of the queue is <DEACTIVATED>, but false if the queue's is <ACTIVATED> or <PULSED>. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue | ( | ACE_Message_Block *& | first_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

| This method is an alias for the following <dequeue_head> method. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_deadline | ( | ACE_Message_Block *& | dequeued,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Dequeue and return the <ACE_Message_Block *> with the lowest deadlien time. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. If the <timeout> elapses without receiving a message -1 is returned and <errno> is set to <EWOULDBLOCK>. If the queue is deactivated -1 is returned and <errno> is set to <ESHUTDOWN>. Otherwise, returns -1 on failure, else the number of items still on the queue.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_deadline_i | ( | ACE_Message_Block *& | first_item | ) | `[protected, virtual]`

| Dequeue and return the <ACE_Message_Block *> with the lowest deadline time.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_head | ( | ACE_Message_Block *& | first_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Dequeue and return the <ACE_Message_Block *> at the head of the queue. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. If the <timeout> elapses without receiving a message -1 is returned and <errno> is set to <EWOULDBLOCK>. If the queue is deactivated -1 is returned and <errno> is set to <ESHUTDOWN>. Otherwise, returns -1 on failure, else the number of items still on the queue.

Implements ACE_Message_Queue_Base.

Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_head_i | ( | ACE_Message_Block *& | first_item | ) | `[protected, virtual]`

| Dequeue and return the <ACE_Message_Block *> at the head of the queue. Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_prio | ( | ACE_Message_Block *& | first_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Dequeue and return the <ACE_Message_Block *> that has the lowest priority. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. If the <timeout> elapses without receiving a message -1 is returned and <errno> is set to <EWOULDBLOCK>. If the queue is deactivated -1 is returned and <errno> is set to <ESHUTDOWN>. Otherwise, returns -1 on failure, else the number of items still on the queue.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_prio_i | ( | ACE_Message_Block *& | dequeued | ) | `[protected, virtual]`

| Dequeue and return the <ACE_Message_Block *> with the lowest priority.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_tail | ( | ACE_Message_Block *& | dequeued,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Dequeue and return the <ACE_Message_Block *> at the tail of the queue. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. If the <timeout> elapses without receiving a message -1 is returned and <errno> is set to <EWOULDBLOCK>. If the queue is deactivated -1 is returned and <errno> is set to <ESHUTDOWN>. Otherwise, returns -1 on failure, else the number of items still on the queue.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::dequeue_tail_i | ( | ACE_Message_Block *& | first_item | ) | `[protected, virtual]`

| Dequeue and return the <ACE_Message_Block *> at the tail of the queue.

template<ACE_SYNCH_DECL >
virtual void ACE_Message_Queue<>::dump | ( | void |  | ) | const`[virtual]`

| Dump the state of an object. Implements ACE_Message_Queue_Base. Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue | ( | ACE_Message_Block * | new_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

| This is an alias for <enqueue_prio>. It's only here for backwards compatibility and will go away in a subsequent release. Please use <enqueue_prio> instead. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_deadline | ( | ACE_Message_Block * | new_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Enqueue an <ACE_Message_Block *> into the <Message_Queue> in accordance with its <msg_deadline_time>. FIFO order is maintained when messages of the same deadline time are inserted consecutively. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. If the <timeout> elapses without receiving a message -1 is returned and <errno> is set to <EWOULDBLOCK>. If the queue is deactivated -1 is returned and <errno> is set to <ESHUTDOWN>. Otherwise, returns -1 on failure, else the number of items still on the queue.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_deadline_i | ( | ACE_Message_Block * | new_item | ) | `[protected, virtual]`

| Enqueue an <ACE_Message_Block *> in accordance with its deadline time.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_head | ( | ACE_Message_Block * | new_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Enqueue an <ACE_Message_Block *> at the head of the queue. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. If the <timeout> elapses without receiving a message -1 is returned and <errno> is set to <EWOULDBLOCK>. If the queue is deactivated -1 is returned and <errno> is set to <ESHUTDOWN>. Otherwise, returns -1 on failure, else the number of items still on the queue.

Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_head_i | ( | ACE_Message_Block * | new_item | ) | `[protected, virtual]`

| Enqueue an <ACE_Message_Block *> at the head of the queue.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_i | ( | ACE_Message_Block * | new_item | ) | `[protected, virtual]`

| Enqueue an <ACE_Message_Block *> in accordance with its priority. Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_prio | ( | ACE_Message_Block * | new_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Enqueue an ACE_Message_Block into the queue in accordance with the ACE_Message_Block's priority (0 is lowest priority). FIFO order is maintained when messages of the same priority are inserted consecutively.

Parameters:

  new_item | Pointer to an ACE_Message_Block that will be added to the queue. The block's `msg_priority()` method will be called to obtain the queueing priority.
  timeout | The absolute time the caller will wait until for the block to be queued.

Return values:

  >0 | The number of ACE_Message_Blocks on the queue after adding the specified block.
  -1 | On failure. errno holds the reason. If EWOULDBLOCK, the timeout elapsed. If ESHUTDOWN, the queue was deactivated or pulsed.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_tail | ( | ACE_Message_Block * | new_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Enqueue an <ACE_Message_Block *> at the end of the queue. Note that <timeout> uses <{absolute}> time rather than <{relative}> time. If the <timeout> elapses without receiving a message -1 is returned and <errno> is set to <EWOULDBLOCK>. If the queue is deactivated -1 is returned and <errno> is set to <ESHUTDOWN>. Otherwise, returns -1 on failure, else the number of items still on the queue.

Implements ACE_Message_Queue_Base.

Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::enqueue_tail_i | ( | ACE_Message_Block * | new_item | ) | `[protected, virtual]`

| Enqueue an <ACE_Message_Block *> at the end of the queue.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::flush | ( | void |  | ) | `[virtual]`

This method holds the queue lock during this operation.

Returns:
  The number of messages flushed.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::flush_i | ( | void |  | ) | `[virtual]`

The caller must be holding the queue lock before calling this method.

Returns:
  The number of messages flushed.

template<ACE_SYNCH_DECL >
virtual void ACE_Message_Queue<>::high_water_mark | ( | size_t | hwm | ) | `[virtual]`

| Set the high watermark, which determines how many bytes can be stored in a queue before it's considered "full."

template<ACE_SYNCH_DECL >
virtual size_t ACE_Message_Queue<>::high_water_mark | ( | void |  | ) | `[virtual]`

| Get high watermark.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::is_empty | ( | void |  | ) | `[virtual]`

| True if queue is empty, else false. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::is_empty_i | ( | void |  | ) | `[protected, virtual]`

| True if queue is empty, else false.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::is_full | ( | void |  | ) | `[virtual]`

| True if queue is full, else false. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::is_full_i | ( | void |  | ) | `[protected, virtual]`

| True if queue is full, else false.

template<ACE_SYNCH_DECL >
virtual ACE_SYNCH_MUTEX_T& ACE_Message_Queue<>::lock | ( | void |  | ) | `[inline, virtual]`

| Returns a reference to the lock used by the <ACE_Message_Queue>.

template<ACE_SYNCH_DECL >
virtual void ACE_Message_Queue<>::low_water_mark | ( | size_t | lwm | ) | `[virtual]`

| Set the low watermark, which determines how many bytes must be in the queue before supplier threads are allowed to enqueue additional <ACE_Message_Block>s.

template<ACE_SYNCH_DECL >
virtual size_t ACE_Message_Queue<>::low_water_mark | ( | void |  | ) | `[virtual]`

| Get low watermark.

template<ACE_SYNCH_DECL >
virtual void ACE_Message_Queue<>::message_bytes | ( | size_t | new_size | ) | `[virtual]`

| New value of the number of total bytes on the queue, i.e., sum of the message block sizes. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual size_t ACE_Message_Queue<>::message_bytes | ( | void |  | ) | `[virtual]`

| Number of total bytes on the queue, i.e., sum of the message block sizes. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::message_count | ( | void |  | ) | `[virtual]`

| Number of total messages on the queue. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual void ACE_Message_Queue<>::message_length | ( | size_t | new_length | ) | `[virtual]`

| New value of the number of total length on the queue, i.e., sum of the message block lengths. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual size_t ACE_Message_Queue<>::message_length | ( | void |  | ) | `[virtual]`

| Number of total length on the queue, i.e., sum of the message block lengths. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual void ACE_Message_Queue<>::notification_strategy | ( | ACE_Notification_Strategy * | s | ) | `[virtual]`

| Set the notification strategy for the <Message_Queue>. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual ACE_Notification_Strategy* ACE_Message_Queue<>::notification_strategy | ( | void |  | ) | `[virtual]`

| Get the notification strategy for the <Message_Queue>. Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::notify | ( | void |  | ) | `[virtual]`

This hook is automatically invoked by <enqueue_head>, <enqueue_tail>, and <enqueue_prio> when a new item is inserted into the queue. Subclasses can override this method to perform specific notification strategies (e.g., signaling events for a <WFMO_Reactor>, notifying a <Reactor>, etc.). In a multi-threaded application with concurrent consumers, there is no guarantee that the queue will be still be non-empty by the time the notification occurs.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::open | ( | size_t | hwm = ACE_Message_Queue_Base::DEFAULT_HWM,
|  | size_t | lwm = ACE_Message_Queue_Base::DEFAULT_LWM,
|  | ACE_Notification_Strategy * | = 0
| ) | `[virtual]`

Initialize an <ACE_Message_Queue>. The <high_water_mark> determines how many bytes can be stored in a queue before it's considered "full." Supplier threads must block until the queue is no longer full. The <low_water_mark> determines how many bytes must be in the queue before supplier threads are allowed to enqueue additional <ACE_Message_Block>s. By default, the <high_water_mark> equals the <low_water_mark>, which means that suppliers will be able to enqueue new messages as soon as a consumer removes any message from the queue. Making the <low_water_mark> smaller than the <high_water_mark> forces consumers to drain more messages from the queue before suppliers can enqueue new messages, which can minimize the "silly window syndrome."

template<ACE_SYNCH_DECL >
void ACE_Message_Queue<>::operator= | ( | const ACE_Message_Queue< _ACE_SYNCH > & |  | ) | `[private]`

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::peek_dequeue_head | ( | ACE_Message_Block *& | first_item,
|  | ACE_Time_Value * | timeout = 0
| ) | `[virtual]`

Retrieve a pointer to the first ACE_Message_Block in the queue without removing it.

Parameters:

  first_item | Reference to an ACE_Message_Block * that will point to the first block on the queue. The block remains on the queue until this or another thread dequeues it.
  timeout | The absolute time the caller will wait until for a block to be queued.

Return values:

  >0 | The number of ACE_Message_Blocks on the queue.
  -1 | On failure. errno holds the reason. If EWOULDBLOCK, the timeout elapsed. If ESHUTDOWN, the queue was deactivated or pulsed.

Implements ACE_Message_Queue_Base.

Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::pulse | ( | void |  | ) | `[virtual]`

Pulse the queue to wake up any waiting threads. Changes the queue state to PULSED; future enqueue/dequeue operations proceed as in ACTIVATED state.

Returns:
  The queue's state before this call.

Implements ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::signal_dequeue_waiters | ( | void |  | ) | `[protected, virtual]`

| Inform any threads waiting to dequeue that they can procede.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::signal_enqueue_waiters | ( | void |  | ) | `[protected, virtual]`

| Inform any threads waiting to enqueue that they can procede.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::state | ( | void |  | ) | `[virtual]`

| Returns the current state of the queue, which can be one of ACTIVATED, DEACTIVATED, or PULSED. Reimplemented from ACE_Message_Queue_Base.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::wait_not_empty_cond | ( | ACE_Guard< ACE_SYNCH_MUTEX_T > & | mon,
|  | ACE_Time_Value * | timeout
| ) | `[protected, virtual]`

| Wait for the queue to become non-empty.

template<ACE_SYNCH_DECL >
virtual int ACE_Message_Queue<>::wait_not_full_cond | ( | ACE_Guard< ACE_SYNCH_MUTEX_T > & | mon,
|  | ACE_Time_Value * | timeout
| ) | `[protected, virtual]`

| Wait for the queue to become non-full.

## Friends And Related Function Documentation

template<ACE_SYNCH_DECL >
friend class ACE_Message_Queue_Iterator< ACE_SYNCH_USE >`[friend]`

template<ACE_SYNCH_DECL >
friend class ACE_Message_Queue_Reverse_Iterator< ACE_SYNCH_USE >`[friend]`

## Member Data Documentation

template<ACE_SYNCH_DECL >
ACE_Message_Queue<>::ACE_ALLOC_HOOK_DECLARE

| Declare the dynamic allocation hooks. Reimplemented from ACE_Message_Queue_Base. Reimplemented in ACE_Dynamic_Message_Queue<>.

template<ACE_SYNCH_DECL >
size_t ACE_Message_Queue<>::cur_bytes_`[protected]`

| Current number of bytes in the queue.

template<ACE_SYNCH_DECL >
int ACE_Message_Queue<>::cur_count_`[protected]`

| Current number of messages in the queue.

template<ACE_SYNCH_DECL >
size_t ACE_Message_Queue<>::cur_length_`[protected]`

| Current length of messages in the queue.

template<ACE_SYNCH_DECL >
ACE_Message_Block* ACE_Message_Queue<>::head_`[protected]`

| Pointer to head of ACE_Message_Block list.

template<ACE_SYNCH_DECL >
size_t ACE_Message_Queue<>::high_water_mark_`[protected]`

| Greatest number of bytes before blocking.

template<ACE_SYNCH_DECL >
ACE_SYNCH_MUTEX_T ACE_Message_Queue<>::lock_`[protected]`

| Protect queue from concurrent access.

template<ACE_SYNCH_DECL >
size_t ACE_Message_Queue<>::low_water_mark_`[protected]`

| Lowest number before unblocking occurs.

template<ACE_SYNCH_DECL >
ACE_SYNCH_CONDITION_T ACE_Message_Queue<>::not_empty_cond_`[protected]`

| Used to make threads sleep until the queue is no longer empty.

template<ACE_SYNCH_DECL >
ACE_SYNCH_CONDITION_T ACE_Message_Queue<>::not_full_cond_`[protected]`

| Used to make threads sleep until the queue is no longer full.

template<ACE_SYNCH_DECL >
ACE_Notification_Strategy* ACE_Message_Queue<>::notification_strategy_`[protected]`

| The notification strategy used when a new message is enqueued.

template<ACE_SYNCH_DECL >
ACE_Message_Block* ACE_Message_Queue<>::tail_`[protected]`

| Pointer to tail of ACE_Message_Block list.

The documentation for this class was generated from the following file:

- /export2/deucetmp/bala/release_try/ACE_wrappers/ace/Message_Queue_T.h