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b1fc9da1c8
replace-object functions are very close to being thread-safe: the only current racy section is the lazy initialization at prepare_replace_object(). The following patches will protect some object reading operations to be called threaded, but before that, replace functions must be protected. To do so, add a mutex to struct raw_object_store and acquire it before lazy initializing the replace_map. This won't cause any noticeable performance drop as the mutex will no longer be used after the replace_map is initialized. Later, when the replace functions are called in parallel, thread debuggers might point our use of the added replace_map_initialized flag as a data race. However, as this boolean variable is initialized as false and it's only updated once, there's no real harm. It's perfectly fine if the value is updated right after a thread read it in replace-map.h:lookup_replace_object() (there'll only be a performance penalty for the affected threads at that moment). We could cease the debugger warning protecting the variable reading at the said function. However, this would negatively affect performance for all threads calling it, at any time, so it's not really worthy since the warning doesn't represent a real problem. Instead, to make sure we don't get false positives (at ThreadSanitizer, at least) an entry for the respective function is added to .tsan-suppressions. Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br> Signed-off-by: Junio C Hamano <gitster@pobox.com>
84 lines
2.2 KiB
C
84 lines
2.2 KiB
C
#include "cache.h"
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#include "oidmap.h"
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#include "object-store.h"
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#include "replace-object.h"
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#include "refs.h"
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#include "repository.h"
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#include "commit.h"
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static int register_replace_ref(struct repository *r,
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const char *refname,
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const struct object_id *oid,
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int flag, void *cb_data)
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{
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/* Get sha1 from refname */
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const char *slash = strrchr(refname, '/');
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const char *hash = slash ? slash + 1 : refname;
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struct replace_object *repl_obj = xmalloc(sizeof(*repl_obj));
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if (get_oid_hex(hash, &repl_obj->original.oid)) {
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free(repl_obj);
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warning(_("bad replace ref name: %s"), refname);
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return 0;
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}
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/* Copy sha1 from the read ref */
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oidcpy(&repl_obj->replacement, oid);
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/* Register new object */
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if (oidmap_put(r->objects->replace_map, repl_obj))
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die(_("duplicate replace ref: %s"), refname);
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return 0;
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}
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void prepare_replace_object(struct repository *r)
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{
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if (r->objects->replace_map_initialized)
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return;
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pthread_mutex_lock(&r->objects->replace_mutex);
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if (r->objects->replace_map_initialized) {
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pthread_mutex_unlock(&r->objects->replace_mutex);
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return;
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}
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r->objects->replace_map =
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xmalloc(sizeof(*r->objects->replace_map));
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oidmap_init(r->objects->replace_map, 0);
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for_each_replace_ref(r, register_replace_ref, NULL);
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r->objects->replace_map_initialized = 1;
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pthread_mutex_unlock(&r->objects->replace_mutex);
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}
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/* We allow "recursive" replacement. Only within reason, though */
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#define MAXREPLACEDEPTH 5
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/*
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* If a replacement for object oid has been set up, return the
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* replacement object's name (replaced recursively, if necessary).
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* The return value is either oid or a pointer to a
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* permanently-allocated value. This function always respects replace
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* references, regardless of the value of read_replace_refs.
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*/
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const struct object_id *do_lookup_replace_object(struct repository *r,
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const struct object_id *oid)
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{
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int depth = MAXREPLACEDEPTH;
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const struct object_id *cur = oid;
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prepare_replace_object(r);
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/* Try to recursively replace the object */
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while (depth-- > 0) {
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struct replace_object *repl_obj =
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oidmap_get(r->objects->replace_map, cur);
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if (!repl_obj)
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return cur;
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cur = &repl_obj->replacement;
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}
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die(_("replace depth too high for object %s"), oid_to_hex(oid));
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}
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