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![Michael Haggerty](/assets/img/avatar_default.png)
Use the reference iterator interface to implement do_for_each_ref(). Delete a bunch of code supporting the old for_each_ref() implementation. And now that do_for_each_ref() is generic code (it is no longer tied to the files backend), move it to refs.c. The implementation is via a new function, do_for_each_ref_iterator(), which takes a reference iterator as argument and calls a callback function for each of the references in the iterator. This change requires the current_ref performance hack for peel_ref() to be implemented via ref_iterator_peel() rather than peel_entry() because we don't have a ref_entry handy (it is hidden under three layers: file_ref_iterator, merge_ref_iterator, and cache_ref_iterator). So: * do_for_each_ref_iterator() records the active iterator in current_ref_iter while it is running. * peel_ref() checks whether current_ref_iter is pointing at the requested reference. If so, it asks the iterator to peel the reference (which it can do efficiently via its "peel" virtual function). For extra safety, we do the optimization only if the refname *addresses* are the same, not only if the refname *strings* are the same, to forestall possible mixups between refnames that come from different ref_iterators. Please note that this optimization of peel_ref() is only available when iterating via do_for_each_ref_iterator() (including all of the for_each_ref() functions, which call it indirectly). It would be complicated to implement a similar optimization when iterating directly using a reference iterator, because multiple reference iterators can be in use at the same time, with interleaved calls to ref_iterator_advance(). (In fact we do exactly that in merge_ref_iterator.) But that is not necessary. peel_ref() is only called while iterating over references. Callers who iterate using the for_each_ref() functions benefit from the optimization described above. Callers who iterate using reference iterators directly have access to the ref_iterator, so they can call ref_iterator_peel() themselves to get an analogous optimization in a more straightforward manner. If we rewrite all callers to use the reference iteration API, then we can remove the current_ref_iter hack permanently. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
385 lines
9.2 KiB
C
385 lines
9.2 KiB
C
/*
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* Generic reference iterator infrastructure. See refs-internal.h for
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* documentation about the design and use of reference iterators.
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*/
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#include "cache.h"
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#include "refs.h"
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#include "refs/refs-internal.h"
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#include "iterator.h"
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int ref_iterator_advance(struct ref_iterator *ref_iterator)
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{
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return ref_iterator->vtable->advance(ref_iterator);
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}
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int ref_iterator_peel(struct ref_iterator *ref_iterator,
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struct object_id *peeled)
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{
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return ref_iterator->vtable->peel(ref_iterator, peeled);
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}
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int ref_iterator_abort(struct ref_iterator *ref_iterator)
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{
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return ref_iterator->vtable->abort(ref_iterator);
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}
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void base_ref_iterator_init(struct ref_iterator *iter,
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struct ref_iterator_vtable *vtable)
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{
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iter->vtable = vtable;
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iter->refname = NULL;
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iter->oid = NULL;
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iter->flags = 0;
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}
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void base_ref_iterator_free(struct ref_iterator *iter)
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{
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/* Help make use-after-free bugs fail quickly: */
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iter->vtable = NULL;
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free(iter);
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}
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struct empty_ref_iterator {
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struct ref_iterator base;
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};
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static int empty_ref_iterator_advance(struct ref_iterator *ref_iterator)
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{
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return ref_iterator_abort(ref_iterator);
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}
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static int empty_ref_iterator_peel(struct ref_iterator *ref_iterator,
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struct object_id *peeled)
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{
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die("BUG: peel called for empty iterator");
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}
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static int empty_ref_iterator_abort(struct ref_iterator *ref_iterator)
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{
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base_ref_iterator_free(ref_iterator);
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return ITER_DONE;
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}
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static struct ref_iterator_vtable empty_ref_iterator_vtable = {
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empty_ref_iterator_advance,
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empty_ref_iterator_peel,
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empty_ref_iterator_abort
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};
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struct ref_iterator *empty_ref_iterator_begin(void)
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{
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struct empty_ref_iterator *iter = xcalloc(1, sizeof(*iter));
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struct ref_iterator *ref_iterator = &iter->base;
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base_ref_iterator_init(ref_iterator, &empty_ref_iterator_vtable);
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return ref_iterator;
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}
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int is_empty_ref_iterator(struct ref_iterator *ref_iterator)
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{
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return ref_iterator->vtable == &empty_ref_iterator_vtable;
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}
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struct merge_ref_iterator {
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struct ref_iterator base;
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struct ref_iterator *iter0, *iter1;
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ref_iterator_select_fn *select;
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void *cb_data;
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/*
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* A pointer to iter0 or iter1 (whichever is supplying the
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* current value), or NULL if advance has not yet been called.
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*/
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struct ref_iterator **current;
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};
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static int merge_ref_iterator_advance(struct ref_iterator *ref_iterator)
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{
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struct merge_ref_iterator *iter =
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(struct merge_ref_iterator *)ref_iterator;
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int ok;
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if (!iter->current) {
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/* Initialize: advance both iterators to their first entries */
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if ((ok = ref_iterator_advance(iter->iter0)) != ITER_OK) {
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iter->iter0 = NULL;
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if (ok == ITER_ERROR)
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goto error;
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}
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if ((ok = ref_iterator_advance(iter->iter1)) != ITER_OK) {
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iter->iter1 = NULL;
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if (ok == ITER_ERROR)
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goto error;
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}
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} else {
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/*
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* Advance the current iterator past the just-used
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* entry:
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*/
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if ((ok = ref_iterator_advance(*iter->current)) != ITER_OK) {
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*iter->current = NULL;
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if (ok == ITER_ERROR)
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goto error;
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}
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}
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/* Loop until we find an entry that we can yield. */
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while (1) {
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struct ref_iterator **secondary;
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enum iterator_selection selection =
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iter->select(iter->iter0, iter->iter1, iter->cb_data);
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if (selection == ITER_SELECT_DONE) {
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return ref_iterator_abort(ref_iterator);
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} else if (selection == ITER_SELECT_ERROR) {
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ref_iterator_abort(ref_iterator);
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return ITER_ERROR;
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}
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if ((selection & ITER_CURRENT_SELECTION_MASK) == 0) {
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iter->current = &iter->iter0;
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secondary = &iter->iter1;
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} else {
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iter->current = &iter->iter1;
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secondary = &iter->iter0;
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}
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if (selection & ITER_SKIP_SECONDARY) {
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if ((ok = ref_iterator_advance(*secondary)) != ITER_OK) {
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*secondary = NULL;
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if (ok == ITER_ERROR)
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goto error;
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}
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}
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if (selection & ITER_YIELD_CURRENT) {
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iter->base.refname = (*iter->current)->refname;
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iter->base.oid = (*iter->current)->oid;
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iter->base.flags = (*iter->current)->flags;
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return ITER_OK;
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}
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}
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error:
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ref_iterator_abort(ref_iterator);
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return ITER_ERROR;
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}
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static int merge_ref_iterator_peel(struct ref_iterator *ref_iterator,
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struct object_id *peeled)
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{
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struct merge_ref_iterator *iter =
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(struct merge_ref_iterator *)ref_iterator;
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if (!iter->current) {
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die("BUG: peel called before advance for merge iterator");
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}
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return ref_iterator_peel(*iter->current, peeled);
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}
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static int merge_ref_iterator_abort(struct ref_iterator *ref_iterator)
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{
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struct merge_ref_iterator *iter =
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(struct merge_ref_iterator *)ref_iterator;
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int ok = ITER_DONE;
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if (iter->iter0) {
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if (ref_iterator_abort(iter->iter0) != ITER_DONE)
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ok = ITER_ERROR;
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}
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if (iter->iter1) {
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if (ref_iterator_abort(iter->iter1) != ITER_DONE)
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ok = ITER_ERROR;
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}
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base_ref_iterator_free(ref_iterator);
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return ok;
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}
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static struct ref_iterator_vtable merge_ref_iterator_vtable = {
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merge_ref_iterator_advance,
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merge_ref_iterator_peel,
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merge_ref_iterator_abort
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};
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struct ref_iterator *merge_ref_iterator_begin(
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struct ref_iterator *iter0, struct ref_iterator *iter1,
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ref_iterator_select_fn *select, void *cb_data)
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{
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struct merge_ref_iterator *iter = xcalloc(1, sizeof(*iter));
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struct ref_iterator *ref_iterator = &iter->base;
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/*
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* We can't do the same kind of is_empty_ref_iterator()-style
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* optimization here as overlay_ref_iterator_begin() does,
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* because we don't know the semantics of the select function.
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* It might, for example, implement "intersect" by passing
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* references through only if they exist in both iterators.
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*/
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base_ref_iterator_init(ref_iterator, &merge_ref_iterator_vtable);
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iter->iter0 = iter0;
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iter->iter1 = iter1;
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iter->select = select;
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iter->cb_data = cb_data;
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iter->current = NULL;
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return ref_iterator;
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}
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/*
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* A ref_iterator_select_fn that overlays the items from front on top
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* of those from back (like loose refs over packed refs). See
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* overlay_ref_iterator_begin().
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*/
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static enum iterator_selection overlay_iterator_select(
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struct ref_iterator *front, struct ref_iterator *back,
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void *cb_data)
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{
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int cmp;
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if (!back)
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return front ? ITER_SELECT_0 : ITER_SELECT_DONE;
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else if (!front)
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return ITER_SELECT_1;
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cmp = strcmp(front->refname, back->refname);
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if (cmp < 0)
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return ITER_SELECT_0;
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else if (cmp > 0)
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return ITER_SELECT_1;
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else
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return ITER_SELECT_0_SKIP_1;
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}
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struct ref_iterator *overlay_ref_iterator_begin(
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struct ref_iterator *front, struct ref_iterator *back)
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{
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/*
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* Optimization: if one of the iterators is empty, return the
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* other one rather than incurring the overhead of wrapping
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* them.
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*/
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if (is_empty_ref_iterator(front)) {
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ref_iterator_abort(front);
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return back;
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} else if (is_empty_ref_iterator(back)) {
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ref_iterator_abort(back);
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return front;
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}
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return merge_ref_iterator_begin(front, back,
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overlay_iterator_select, NULL);
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}
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struct prefix_ref_iterator {
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struct ref_iterator base;
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struct ref_iterator *iter0;
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char *prefix;
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int trim;
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};
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static int prefix_ref_iterator_advance(struct ref_iterator *ref_iterator)
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{
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struct prefix_ref_iterator *iter =
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(struct prefix_ref_iterator *)ref_iterator;
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int ok;
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while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
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if (!starts_with(iter->iter0->refname, iter->prefix))
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continue;
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iter->base.refname = iter->iter0->refname + iter->trim;
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iter->base.oid = iter->iter0->oid;
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iter->base.flags = iter->iter0->flags;
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return ITER_OK;
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}
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iter->iter0 = NULL;
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if (ref_iterator_abort(ref_iterator) != ITER_DONE)
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return ITER_ERROR;
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return ok;
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}
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static int prefix_ref_iterator_peel(struct ref_iterator *ref_iterator,
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struct object_id *peeled)
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{
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struct prefix_ref_iterator *iter =
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(struct prefix_ref_iterator *)ref_iterator;
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return ref_iterator_peel(iter->iter0, peeled);
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}
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static int prefix_ref_iterator_abort(struct ref_iterator *ref_iterator)
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{
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struct prefix_ref_iterator *iter =
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(struct prefix_ref_iterator *)ref_iterator;
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int ok = ITER_DONE;
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if (iter->iter0)
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ok = ref_iterator_abort(iter->iter0);
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free(iter->prefix);
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base_ref_iterator_free(ref_iterator);
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return ok;
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}
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static struct ref_iterator_vtable prefix_ref_iterator_vtable = {
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prefix_ref_iterator_advance,
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prefix_ref_iterator_peel,
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prefix_ref_iterator_abort
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};
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struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
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const char *prefix,
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int trim)
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{
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struct prefix_ref_iterator *iter;
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struct ref_iterator *ref_iterator;
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if (!*prefix && !trim)
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return iter0; /* optimization: no need to wrap iterator */
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iter = xcalloc(1, sizeof(*iter));
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ref_iterator = &iter->base;
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base_ref_iterator_init(ref_iterator, &prefix_ref_iterator_vtable);
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iter->iter0 = iter0;
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iter->prefix = xstrdup(prefix);
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iter->trim = trim;
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return ref_iterator;
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}
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struct ref_iterator *current_ref_iter = NULL;
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int do_for_each_ref_iterator(struct ref_iterator *iter,
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each_ref_fn fn, void *cb_data)
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{
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int retval = 0, ok;
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struct ref_iterator *old_ref_iter = current_ref_iter;
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current_ref_iter = iter;
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while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
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retval = fn(iter->refname, iter->oid, iter->flags, cb_data);
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if (retval) {
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/*
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* If ref_iterator_abort() returns ITER_ERROR,
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* we ignore that error in deference to the
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* callback function's return value.
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*/
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ref_iterator_abort(iter);
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goto out;
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}
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}
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out:
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current_ref_iter = old_ref_iter;
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if (ok == ITER_ERROR)
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return -1;
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return retval;
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}
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