tag: lock all accesses to tag_pool

The tag pool is a shared global resource that is infrequently
modified.  However, it can occasionally be modified by several
threads, especially by the metadata_pipe for streaming metadata
(both reading/writing).

The bulk tag_item pool is NOT locked as currently only the
update thread uses it.

3 files changed, 15 insertions, 6 deletions

diff --git a/src/tag.c b/src/tag.c
index 45a2687cb..35835f1a1 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -244,8 +244,9 @@ static void deleteItem(struct tag *tag, int idx)
 	assert(idx < tag->numOfItems);
 	tag->numOfItems--;
 
+	pthread_mutex_lock(&tag_pool_lock);
 	tag_pool_put_item(tag->items[idx]);
-	/* free(tag->items[idx].value); */
+	pthread_mutex_unlock(&tag_pool_lock);
 
 	if (tag->numOfItems - idx > 0) {
 		memmove(tag->items + idx, tag->items + idx + 1,
@@ -277,10 +278,10 @@ static void clearMpdTag(struct tag *tag)
 {
 	int i;
 
-	for (i = 0; i < tag->numOfItems; i++) {
-		/* free(tag->items[i].value); */
+	pthread_mutex_lock(&tag_pool_lock);
+	for (i = 0; i < tag->numOfItems; i++)
 		tag_pool_put_item(tag->items[i]);
-	}
+	pthread_mutex_unlock(&tag_pool_lock);
 
 	if (tag->items == bulk.items) {
 #ifndef NDEBUG
@@ -317,9 +318,10 @@ struct tag *tag_dup(const struct tag *tag)
 	ret->numOfItems = tag->numOfItems;
 	ret->items = ret->numOfItems > 0 ? xmalloc(items_size(tag)) : NULL;
 
-	for (i = 0; i < tag->numOfItems; i++) {
+	pthread_mutex_lock(&tag_pool_lock);
+	for (i = 0; i < tag->numOfItems; i++)
 		ret->items[i] = tag_pool_dup_item(tag->items[i]);
-	}
+	pthread_mutex_unlock(&tag_pool_lock);
 
 	return ret;
 }
@@ -428,7 +430,9 @@ static void appendToTagItems(struct tag *tag, enum tag_type type,
 		       items_size(tag) - sizeof(struct tag_item));
 	}
 
+	pthread_mutex_lock(&tag_pool_lock);
 	tag->items[i] = tag_pool_get_item(type, p, len);
+	pthread_mutex_unlock(&tag_pool_lock);
 
 	if (p != value)
 		xfree(p);
diff --git a/src/tag_pool.c b/src/tag_pool.c
index 89efef1fc..d227a2988 100644
--- a/src/tag_pool.c
+++ b/src/tag_pool.c
@@ -19,6 +19,8 @@
 #include "tag_pool.h"
 #include "utils.h"
 
+pthread_mutex_t tag_pool_lock = PTHREAD_MUTEX_INITIALIZER;
+
 #define NUM_SLOTS 4096
 
 struct slot {
diff --git a/src/tag_pool.h b/src/tag_pool.h
index e19b2f4b4..d837d4446 100644
--- a/src/tag_pool.h
+++ b/src/tag_pool.h
@@ -20,6 +20,9 @@
 #define TAG_POOL_H
 
 #include "tag.h"
+#include "os_compat.h"
+
+extern pthread_mutex_t tag_pool_lock;
 
 struct tag_item;