scrcpy/app/src/queue.h
Romain Vimont b0184f2869 Initialize queue "last" field
The compiler is not always able to see that "last" is always initialized
before being used, so always initialize it.
2019-08-04 16:22:39 +02:00

74 lines
1.9 KiB
C

// generic intrusive FIFO queue
#ifndef QUEUE_H
#define QUEUE_H
#include <stdbool.h>
#include <SDL2/SDL_assert.h>
// To define a queue type of "struct foo":
// struct queue_foo QUEUE(struct foo);
#define QUEUE(TYPE) { \
TYPE *first; \
TYPE *last; \
}
#define queue_init(PQ) \
(void) ((PQ)->first = (PQ)->last = NULL)
#define queue_is_empty(PQ) \
!(PQ)->first
// NEXTFIELD is the field in the ITEM type used for intrusive linked-list
//
// For example:
// struct foo {
// int value;
// struct foo *next;
// };
//
// // define the type "struct my_queue"
// struct my_queue QUEUE(struct foo);
//
// struct my_queue queue;
// queue_init(&queue);
//
// struct foo v1 = { .value = 42 };
// struct foo v2 = { .value = 27 };
//
// queue_push(&queue, next, v1);
// queue_push(&queue, next, v2);
//
// struct foo *foo;
// queue_take(&queue, next, &foo);
// assert(foo->value == 42);
// queue_take(&queue, next, &foo);
// assert(foo->value == 27);
// assert(queue_is_empty(&queue));
//
// push a new item into the queue
#define queue_push(PQ, NEXTFIELD, ITEM) \
(void) ({ \
(ITEM)->NEXTFIELD = NULL; \
if (queue_is_empty(PQ)) { \
(PQ)->first = (PQ)->last = (ITEM); \
} else { \
(PQ)->last->NEXTFIELD = (ITEM); \
(PQ)->last = (ITEM); \
} \
})
// take the next item and remove it from the queue (the queue must not be empty)
// the result is stored in *(PITEM)
// (without typeof(), we could not store a local variable having the correct
// type so that we can "return" it)
#define queue_take(PQ, NEXTFIELD, PITEM) \
(void) ({ \
SDL_assert(!queue_is_empty(PQ)); \
*(PITEM) = (PQ)->first; \
(PQ)->first = (PQ)->first->NEXTFIELD; \
})
// no need to update (PQ)->last if the queue is left empty:
// (PQ)->last is undefined if !(PQ)->first anyway
#endif