From bde64a13e24f1bfc6d9319b916b304ad434cd027 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Thu, 5 Aug 2021 14:30:07 +0200
Subject: [PATCH] tag/Builder: do not acquire tag_pool_lock if TagItem list is
empty
---
src/tag/Builder.cxx | 41 +++++++++++++++++++++++++++--------------
1 file changed, 27 insertions(+), 14 deletions(-)
diff --git a/src/tag/Builder.cxx b/src/tag/Builder.cxx
index e5e380399..b2887c903 100644
--- a/src/tag/Builder.cxx
+++ b/src/tag/Builder.cxx
@@ -36,10 +36,12 @@ TagBuilder::TagBuilder(const Tag &other) noexcept
{
items.reserve(other.num_items);
- const std::lock_guard<Mutex> protect(tag_pool_lock);
-
- for (unsigned i = 0, n = other.num_items; i != n; ++i)
- items.push_back(tag_pool_dup_item(other.items[i]));
+ const std::size_t n = other.num_items;
+ if (n > 0) {
+ const std::lock_guard<Mutex> protect(tag_pool_lock);
+ for (std::size_t i = 0; i != n; ++i)
+ items.push_back(tag_pool_dup_item(other.items[i]));
+ }
}
TagBuilder::TagBuilder(Tag &&other) noexcept
@@ -65,12 +67,15 @@ TagBuilder::operator=(const TagBuilder &other) noexcept
has_playlist = other.has_playlist;
RemoveAll();
- items = other.items;
- /* increment the tag pool refcounters */
- const std::lock_guard<Mutex> protect(tag_pool_lock);
- for (auto &i : items)
- i = tag_pool_dup_item(i);
+ if (!other.items.empty()) {
+ items = other.items;
+
+ /* increment the tag pool refcounters */
+ const std::lock_guard<Mutex> protect(tag_pool_lock);
+ for (auto &i : items)
+ i = tag_pool_dup_item(i);
+ }
return *this;
}
@@ -181,11 +186,14 @@ TagBuilder::Complement(const Tag &other) noexcept
items.reserve(items.size() + other.num_items);
- const std::lock_guard<Mutex> protect(tag_pool_lock);
- for (unsigned i = 0, n = other.num_items; i != n; ++i) {
- TagItem *item = other.items[i];
- if (!present[item->type])
- items.push_back(tag_pool_dup_item(item));
+ const std::size_t n = other.num_items;
+ if (n > 0) {
+ const std::lock_guard<Mutex> protect(tag_pool_lock);
+ for (std::size_t i = 0; i != n; ++i) {
+ TagItem *item = other.items[i];
+ if (!present[item->type])
+ items.push_back(tag_pool_dup_item(item));
+ }
}
}
@@ -245,6 +253,11 @@ TagBuilder::AddEmptyItem(TagType type) noexcept
void
TagBuilder::RemoveAll() noexcept
{
+ if (items.empty())
+ /* don't acquire the tag_pool_lock if we're not going
+ to call tag_pool_put_item() anyway */
+ return;
+
{
const std::lock_guard<Mutex> protect(tag_pool_lock);
for (auto i : items)