[GSoC][PATCH 3/4] grep: disable grep_read_mutex when possible

[Matheus Tavares]

git-grep uses 'grep_read_mutex' to protect some object reading
operations. But these have their own internal lock now, which ensure a
better performance (with more parallel regions). So, disable the former
when it's possible to use the latter, with enable_obj_read_lock().

Signed-off-by: Matheus Tavares <matheus.bernard...@usp.br>
---
 builtin/grep.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index a871bad8ad..fa51392222 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -205,7 +205,17 @@ static void start_threads(struct grep_opt *opt)
        pthread_cond_init(&cond_add, NULL);
        pthread_cond_init(&cond_write, NULL);
        pthread_cond_init(&cond_result, NULL);
-       grep_use_locks = GREP_USE_ALL_LOCKS;
+       if (recurse_submodules || opt->allow_textconv) {
+               /*
+                * textconv and submodules' operations are not thread-safe yet
+                * so we must use grep_read_lock when grepping multithreaded
+                * with these options.
+                */
+               grep_use_locks = GREP_USE_ALL_LOCKS;
+       } else {
+               grep_use_locks = GREP_USE_ATTR_LOCK;
+               enable_obj_read_lock();
+       }
 
        for (i = 0; i < ARRAY_SIZE(todo); i++) {
                strbuf_init(&todo[i].out, 0);
@@ -227,7 +237,7 @@ static void start_threads(struct grep_opt *opt)
        }
 }
 
-static int wait_all(void)
+static int wait_all(struct grep_opt *opt)
 {
        int hit = 0;
        int i;
@@ -263,6 +273,9 @@ static int wait_all(void)
        pthread_cond_destroy(&cond_write);
        pthread_cond_destroy(&cond_result);
        grep_use_locks = 0;
+       if (!recurse_submodules && !opt->allow_textconv) {
+               disable_obj_read_lock();
+       }
 
        return hit;
 }
@@ -1140,7 +1153,7 @@ int cmd_grep(int argc, const char **argv, const char 
*prefix)
        }
 
        if (num_threads > 1)
-               hit |= wait_all();
+               hit |= wait_all(&opt);
        if (hit && show_in_pager)
                run_pager(&opt, prefix);
        clear_pathspec(&pathspec);
-- 
2.22.0