perf machine: Introduce number of threads member

To be used, for instance, for pre-allocating an rb_tree array for
sorting by other keys besides the current pid one.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ja0ifkwue7ttjhbwijn6g6eu@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/machine.c

@@ -32,6 +32,7 @@ int machine__init(struct machine *machine, const char *root_dir, pid_t pid)
 
 	machine->threads = RB_ROOT;
 	pthread_rwlock_init(&machine->threads_lock, NULL);
+	machine->nr_threads = 0;
 	INIT_LIST_HEAD(&machine->dead_threads);
 	machine->last_match = NULL;
 
@@ -430,6 +431,7 @@ static struct thread *____machine__findnew_thread(struct machine *machine,
 		 */
 		thread__get(th);
 		machine->last_match = th;
+		++machine->nr_threads;
 	}
 
 	return th;
@@ -681,11 +683,13 @@ size_t machine__fprintf_vmlinux_path(struct machine *machine, FILE *fp)
 
 size_t machine__fprintf(struct machine *machine, FILE *fp)
 {
-	size_t ret = 0;
+	size_t ret;
 	struct rb_node *nd;
 
 	pthread_rwlock_rdlock(&machine->threads_lock);
 
+	ret = fprintf(fp, "Threads: %u\n", machine->nr_threads);
+
 	for (nd = rb_first(&machine->threads); nd; nd = rb_next(nd)) {
 		struct thread *pos = rb_entry(nd, struct thread, rb_node);
 
@@ -1419,6 +1423,7 @@ static void __machine__remove_thread(struct machine *machine, struct thread *th,
 		pthread_rwlock_wrlock(&machine->threads_lock);
 	rb_erase_init(&th->rb_node, &machine->threads);
 	RB_CLEAR_NODE(&th->rb_node);
+	--machine->nr_threads;
 	/*
 	 * Move it first to the dead_threads list, then drop the reference,
 	 * if this is the last reference, then the thread__delete destructor

tools/perf/util/machine.h

@@ -31,6 +31,7 @@ struct machine {
 	char		  *root_dir;
 	struct rb_root	  threads;
 	pthread_rwlock_t  threads_lock;
+	unsigned int	  nr_threads;
 	struct list_head  dead_threads;
 	struct thread	  *last_match;
 	struct vdso_info  *vdso_info;