C Image Processing Library
Implements queue of generic pointers. More...
|L_QUEUE *||lqueueCreate (l_int32 nalloc)|
|void||lqueueDestroy (L_QUEUE **plq, l_int32 freeflag)|
|l_int32||lqueueAdd (L_QUEUE *lq, void *item)|
|l_int32||lqueueExtendArray (L_QUEUE *lq)|
|void *||lqueueRemove (L_QUEUE *lq)|
|l_int32||lqueueGetCount (L_QUEUE *lq)|
|l_int32||lqueuePrint (FILE *fp, L_QUEUE *lq)|
|static const l_int32||MIN_BUFFER_SIZE = 20|
|static const l_int32||INITIAL_BUFFER_ARRAYSIZE = 1024|
Implements queue of generic pointers.
Create/Destroy L_Queue L_QUEUE *lqueueCreate() void *lqueueDestroy() Operations to add/remove to/from a L_Queue l_int32 lqueueAdd() l_int32 lqueueExtendArray() void *lqueueRemove() Accessors l_int32 lqueueGetCount() Debug output l_int32 lqueuePrint() The lqueue is a fifo that implements a queue of void* pointers. It can be used to hold a queue of any type of struct. Internally, it maintains two counters: nhead: location of head (in ptrs) from the beginning of the buffer nelem: number of ptr elements stored in the queue As items are added to the queue, nelem increases. As items are removed, nhead increases and nelem decreases. Any time the tail reaches the end of the allocated buffer, all the pointers are shifted to the left, so that the head is at the beginning of the array. If the buffer becomes more than 3/4 full, it doubles in size. [A circular queue would allow us to skip the shifting and to resize only when the buffer is full. For most applications, the extra work we do for a linear queue is not significant.]
Definition in file queue.c.
Input: size of ptr array to be alloc'd (0 for default) Return: lqueue, or null on error
Notes: (1) Allocates a ptr array of given size, and initializes counters.
Input: &lqueue (<to be="" nulled>="">) freeflag (TRUE to free each remaining struct in the array) Return: void
Notes: (1) If freeflag is TRUE, frees each struct in the array. (2) If freeflag is FALSE but there are elements on the array, gives a warning and destroys the array. This will cause a memory leak of all the items that were on the queue. So if the items require their own destroy function, they must be destroyed before the queue. The same applies to the auxiliary stack, if it is used. (3) To destroy the L_Queue, we destroy the ptr array, then the lqueue, and then null the contents of the input ptr.
Input: lqueue item to be added to the tail of the queue Return: 0 if OK, 1 on error
Notes: (1) The algorithm is as follows. If the queue is populated to the end of the allocated array, shift all ptrs toward the beginning of the array, so that the head of the queue is at the beginning of the array. Then, if the array is more than 0.75 full, realloc with double the array size. Finally, add the item to the tail of the queue.
|void* lqueueRemove||(||L_QUEUE *||lq||)|
Input: lqueue Return: ptr to item popped from the head of the queue, or null if the queue is empty or on error
Notes: (1) If this is the last item on the queue, so that the queue becomes empty, nhead is reset to the beginning of the array.