NAME

       globus_priority_q - Priority Queue

        - Priority Queue.

SYNOPSIS

   Data Structures
       struct globus_priority_q_s
           Priority Queue Structure.

   Typedefs
       typedef int(* globus_priority_q_cmp_func_t) (void *priority_1, void *priority_2)
           Priority Comparison Predicate.
       typedef struct globus_priority_q_s globus_priority_q_t
           Priority Queue Structure.

   Functions
       int globus_priority_q_init (globus_priority_q_t *priority_q, globus_priority_q_cmp_func_t
           cmp_func)
           Initialize a priority queue.
       int globus_priority_q_destroy (globus_priority_q_t *priority_q)
           Destroy a Priority Queue.
       globus_bool_t globus_priority_q_empty (globus_priority_q_t *priority_q)
           Priority Queue Empty Predicate.
       int globus_priority_q_size (globus_priority_q_t *priority_q)
           Priority Queue Size.
       int globus_priority_q_enqueue (globus_priority_q_t *priority_q, void *datum, void
           *priority)
           Add a Datum to a Priority Queue.
       void * globus_priority_q_dequeue (globus_priority_q_t *priority_q)
           Remove a Datum From A Priority Queue.
       void * globus_priority_q_first (globus_priority_q_t *priority_q)
           Get the Highest-Priority Datum From a Priority Queue.
       void * globus_priority_q_first_priority (globus_priority_q_t *priority_q)
           Get the Highest Priority in Priority Queue.
       void * globus_priority_q_remove (globus_priority_q_t *priority_q, void *datum)
           Remove an Arbitrary Datum from a Priority Queue.
       void * globus_priority_q_modify (globus_priority_q_t *priority_q, void *datum, void
           *new_priority)
           Modify the Priority of Datum.

Detailed Description

       Priority Queue.

       This module defines a priority queue for globus. It is implemented using a binary heap
       (minheap) and does NOT have a fifo fallback for like priorities. If you need fifo
       fallback, you should use a compound priority with the primary priority being the 'real'
       priority and the secondary being a serial number.

       To use this priority queue type, define a comparison function of type
       globus_priority_q_cmp_func_t and pass that to globus_priority_q_init().

       To add and remove items in priority order, use globus_priority_q_enqueue() and
       globus_priority_q_dequeue() respectively.

       To remove a datum ignoring its priority, use globus_priority_q_remove().

       To inspect the first element and its priority, use globus_priority_q_first() and
       globus_priority_q_first_priority() respectively.

       To determine whether a queue is empty or the number of data in it, use
       globus_priority_q_empty() and globus_priority_q_size().

       To modify the priority of a datum already in the queue, use globus_priority_q_modify().

       When finished with the queue, use globus_priority_q_destroy() to free data associated with
       the priority queue.

Typedef Documentation

   typedef int(* globus_priority_q_cmp_func_t) (void *priority_1, void *priority_2)
       Priority Comparison Predicate. This type is used to implement comparison of two priorities
       for inserting items into the priority queue. A function of this type is passed to
       globus_priority_q_init() to determine how priorities are computed in a newly created
       priority queue.

       Parameters
           priority_1 First priority to compare
           priority_2 Second priority to compare

       Return values
           > 0 The priority of priority_1 is less than that of priority_2.
           < 0 The priority of priority_1 is greater than that of priority_2.
           = 0 The priorities of priority_1 and priority_2 are the same.

   typedef struct globus_priority_q_s globus_priority_q_t
       Priority Queue Structure. A pointer to a structure of this type is passed to all functions
       in the Priority Queue  module. It is not intended to be inspected or modified outside of
       this API.

Function Documentation

   void * globus_priority_q_dequeue (globus_priority_q_t * priority_q)
       Remove a Datum From A Priority Queue. The globus_priority_q_dequeue() function removes the
       highest-priority datum from the given priority queue and returns it. If the priority_q
       pointer is NULL or the priority queue is empty, this function returns NULL.

       Parameters
           priority_q Pointer to the priority queue to remove from.

       Returns
           This function returns the highest-priority datum from the priority queue.

   int globus_priority_q_destroy (globus_priority_q_t * priority_q)
       Destroy a Priority Queue. The globus_priority_q_destroy() function destroys the contents
       of a priority queue. After this function returns, the structure pointed to by priority_q
       is invalid and must not be passed to any functions in the Priority Queue  module other
       globus_priority_q_init().

       Note that this function does not call any destructors for the data inserted into the
       priority queue, so the caller must be sure to either have other references to those data
       or free them before calling this function.

       Parameters
           priority_q Pointer to the priority_q to destroy.

       Return values
           GLOBUS_SUCCESS Success
           GLOBUS_FAILURE Failure

   globus_bool_t globus_priority_q_empty (globus_priority_q_t * priority_q)
       Priority Queue Empty Predicate. The globus_priority_q_empty() function checks the given
       priority queue to determine if it is empty. It is considered empty if it has been
       initialized via globus_priority_q_init() and there are no items which have been inserted
       via globus_priority_q_enqueue() which have not been removed by calling
       globus_priority_q_remove() or globus_priority_q_dequeue(). If it is empty, this function
       returns GLOBUS_TRUE; otherwise it returns GLOBUS_FALSE.

       Parameters
           priority_q Pointer to the priority queue to check

       Return values
           GLOBUS_TRUE The priority queue is empty
           GLOBUS_FALSE The priority queue is not empty, or the priority queue is invalid

   int globus_priority_q_enqueue (globus_priority_q_t * priority_q, void * datum, void *
       priority)
       Add a Datum to a Priority Queue. The globus_priority_q_enqueue() function inserts a datum
       into the priority queue based on its priority. When an item is inserted, the pointers to
       both the datum and the priority are copied into the priority_q data structure, so neither
       may be freed until the datum is removed from the priority queue, or undefined behavior may
       occur.

       Note that there is no fifo fallback for priorities, so the order of two items with
       equivalent priorities is not specified relative to each other. To enable fifo fallback,
       use a compound priority that includes a priority level and a sequence number as the value
       pointed to by the priority parameter and pass a suitable comparison function to initialize
       the priority queue.

       Parameters
           priority_q Pointer to the priority queue to insert datum into
           datum The datum to insert into the queue
           priority The priority of the datum

       Return values
           GLOBUS_SUCCESS Success
           GLOBUS_FAILURE Failure

   void * globus_priority_q_first (globus_priority_q_t * priority_q)
       Get the Highest-Priority Datum From a Priority Queue. The globus_priority_q_first()
       function returns the highest-priority datum from the priority queue pointed to by
       priority_q. The datum is not removed from the queue; to do that, use
       globus_priority_q_dequeue() instead. If the priority_q pointer is NULL or the queue is
       empty, this function returns NULL. The priority queue retains a reference to the returned
       datum, so the pointer value returned must not freed until the datum is removed from the
       queue.

       Parameters
           priority_q Pointer to the priority queue to inspect

       Returns
           This function returns the highest-priority datum from the priority queue.

   void * globus_priority_q_first_priority (globus_priority_q_t * priority_q)
       Get the Highest Priority in Priority Queue. The globus_priority_q_first_priority()
       function returns the value of highest priority in the priority queue (not the datum
       associated with that priority). If the priority_q pointer is NULL or empty, this function
       returns NULL. The priority queue retains a reference to the returned priority, so the
       pointer value returned must not be freed until the datum associated with it is removed
       from the queue.

       Parameters
           priority_q Pointer to the priority queue to inspect

       Returns
           This function returns the highest priority value in the priority queue.

   int globus_priority_q_init (globus_priority_q_t * priority_q, globus_priority_q_cmp_func_t
       cmp_func)
       Initialize a priority queue. The globus_priority_q_init() function initializes a
       globus_priority_q_t structure for use with the other functions in the Priority Queue
       module. If this function returns GLOBUS_SUCCESS, the caller is responsible for
       deallocating the members of this structure when it is no longer needed by passing it to
       globus_priority_q_destroy().

       Parameters
           priority_q Pointer to the priority queue structure to initialize.
           cmp_func Pointer to a function which computes the relative relationship between two
           priorities. See the documentation of globus_priority_q_cmp_func_t for details on how
           to implement that function.

       Return values
           GLOBUS_SUCCESS Success
           GLOBUS_FAILURE Failure

   void * globus_priority_q_modify (globus_priority_q_t * priority_q, void * datum, void *
       new_priority)
       Modify the Priority of Datum. The globus_priority_q_modify() function modifies the
       priority of the highest-priority instance of datum in the priority queue so that it
       new_priority. The old priority of the datum is returned. If the priority_q is NULL or the
       datum is not present, this function returns NULL.

       Parameters
           priority_q Pointer to the priority queue to modify
           datum Pointer to the datum whose priority is being modified
           new_priority Pointer to the new priority

       Returns
           This function returns the old priority of datum.

   void * globus_priority_q_remove (globus_priority_q_t * priority_q, void * datum)
       Remove an Arbitrary Datum from a Priority Queue. The globus_priority_q_remove() function
       removes the highest-priority instance of the specified datum from the priority queue and
       returns the datum if it is found. If the priority_q is NULL or the datum is not found,
       this function returns NULL.

       Parameters
           priority_q Pointer to the priority queue to modify
           datum Pointer to the datum to search for.

       Returns
           This function returns datum if it was present in the priority queue

   int globus_priority_q_size (globus_priority_q_t * priority_q)
       Priority Queue Size. The globus_priority_q_size() function returns the size of the
       priority queue, that is, the number of elements that are currently enqueued in it. The
       special value GLOBUS_FAILURE is returned if a null pointer is passed to this function.

       Parameters
           priority_q Pointer to the priority queue to check

       Returns
           This function returns the number of elements in the queue, or GLOBUS_FAILURE if the
           priority_q pointer is invalid.

Author

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