grep: clean up num_threads handling

When NO_PTHREADS is still used in this file, we have two separate code
paths for thread and no thread support. The latter will always have
num_threads remain zero while the former uses num_threads zero as
"default number of threads".

With recent changes blur the line between thread and no-thread
support, this num_threads handling becomes a bit strange so let's
redefine it like this:

- num_threads == 0 means default number of threads and should become
  positive after all configuration and option parsing is done if
  multithread is supported.

- num_threads <= 1 runs no threads. It does not matter if the platform
  supports threading or not.

- num_threads > 1 will run multiple threads and is invalid if
  HAVE_THREADS is false. pthread API is only used in this case.

PS. a new warning is also added when num_threads is forced back to one
because a thread-incompatible option is specified.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/grep.c b/builtin/grep.c
index 6dd15dbaa264ce98540c8e43ecebec0763c2876d..de3f568cee3afdfd1a7f13196e2e93b5712dcd9b 100644 (file)
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -69,13 +69,11 @@ static pthread_mutex_t grep_mutex;
 
 static inline void grep_lock(void)
 {
-       assert(num_threads);
        pthread_mutex_lock(&grep_mutex);
 }
 
 static inline void grep_unlock(void)
 {
-       assert(num_threads);
        pthread_mutex_unlock(&grep_mutex);
 }
 
@@ -234,7 +232,7 @@ static int wait_all(void)
        int i;
 
        if (!HAVE_THREADS)
-               return 0;
+               BUG("Never call this function unless you have started threads");
 
        grep_lock();
        all_work_added = 1;
@@ -279,14 +277,14 @@ static int grep_cmd_config(const char *var, const char *value, void *cb)
                if (num_threads < 0)
                        die(_("invalid number of threads specified (%d) for %s"),
                            num_threads, var);
-               else if (!HAVE_THREADS && num_threads && num_threads != 1) {
+               else if (!HAVE_THREADS && num_threads > 1) {
                        /*
                         * TRANSLATORS: %s is the configuration
                         * variable for tweaking threads, currently
                         * grep.threads
                         */
                        warning(_("no threads support, ignoring %s"), var);
-                       num_threads = 0;
+                       num_threads = 1;
                }
        }
 
@@ -323,7 +321,7 @@ static int grep_oid(struct grep_opt *opt, const struct object_id *oid,
        grep_source_init(&gs, GREP_SOURCE_OID, pathbuf.buf, path, oid);
        strbuf_release(&pathbuf);
 
-       if (HAVE_THREADS && num_threads) {
+       if (num_threads > 1) {
                /*
                 * add_work() copies gs and thus assumes ownership of
                 * its fields, so do not call grep_source_clear()
@@ -353,7 +351,7 @@ static int grep_file(struct grep_opt *opt, const char *filename)
        grep_source_init(&gs, GREP_SOURCE_FILE, buf.buf, filename, filename);
        strbuf_release(&buf);
 
-       if (HAVE_THREADS && num_threads) {
+       if (num_threads > 1) {
                /*
                 * add_work() copies gs and thus assumes ownership of
                 * its fields, so do not call grep_source_clear()
@@ -1025,36 +1023,34 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
        pathspec.recursive = 1;
        pathspec.recurse_submodules = !!recurse_submodules;
 
-       if (HAVE_THREADS) {
-               if (list.nr || cached || show_in_pager)
-                       num_threads = 0;
-               else if (num_threads == 0)
-                       num_threads = GREP_NUM_THREADS_DEFAULT;
-               else if (num_threads < 0)
-                       die(_("invalid number of threads specified (%d)"), num_threads);
-               if (num_threads == 1)
-                       num_threads = 0;
+       if (list.nr || cached || show_in_pager) {
+               if (num_threads > 1)
+                       warning(_("invalid option combination, ignoring --threads"));
+               num_threads = 1;
+       } else if (!HAVE_THREADS && num_threads > 1) {
+               warning(_("no threads support, ignoring --threads"));
+               num_threads = 1;
+       } else if (num_threads < 0)
+               die(_("invalid number of threads specified (%d)"), num_threads);
+       else if (num_threads == 0)
+               num_threads = HAVE_THREADS ? GREP_NUM_THREADS_DEFAULT : 1;
+
+       if (num_threads > 1) {
+               if (!HAVE_THREADS)
+                       BUG("Somebody got num_threads calculation wrong!");
+               if (!(opt.name_only || opt.unmatch_name_only || opt.count)
+                   && (opt.pre_context || opt.post_context ||
+                       opt.file_break || opt.funcbody))
+                       skip_first_line = 1;
+               start_threads(&opt);
        } else {
-               if (num_threads)
-                       warning(_("no threads support, ignoring --threads"));
-               num_threads = 0;
-       }
-
-       if (!num_threads)
                /*
                 * The compiled patterns on the main path are only
                 * used when not using threading. Otherwise
-                * start_threads() below calls compile_grep_patterns()
+                * start_threads() above calls compile_grep_patterns()
                 * for each thread.
                 */
                compile_grep_patterns(&opt);
-
-       if (HAVE_THREADS && num_threads) {
-               if (!(opt.name_only || opt.unmatch_name_only || opt.count)
-                   && (opt.pre_context || opt.post_context ||
-                       opt.file_break || opt.funcbody))
-                       skip_first_line = 1;
-               start_threads(&opt);
        }
 
        if (show_in_pager && (cached || list.nr))
@@ -1106,7 +1102,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
                hit = grep_objects(&opt, &pathspec, &list);
        }
 
-       if (num_threads)
+       if (num_threads > 1)
                hit |= wait_all();
        if (hit && show_in_pager)
                run_pager(&opt, prefix);