Make links and nodes thread-safe + add a getter for links

src/main/kotlin/dev/arbjerg/lavalink/client/LavalinkClient.kt

@@ -11,21 +11,26 @@ import reactor.core.publisher.Flux
 import reactor.core.publisher.Sinks
 import java.io.Closeable
 import java.net.URI
+import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.CopyOnWriteArrayList
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
 
 /**
  * @param userId ID of the bot for authenticating with Discord
  */
 class LavalinkClient(val userId: Long) : Closeable, Disposable {
-    private val internalNodes = mutableListOf<LavalinkNode>()
-    private val links = mutableMapOf<Long, Link>()
+    private val internalNodes = CopyOnWriteArrayList<LavalinkNode>()
+    private val linkMap = ConcurrentHashMap<Long, Link>()
     private var clientOpen = true
 
     // Immutable public list
     val nodes: List<LavalinkNode>
         get() = internalNodes.toList()
 
+    val links: List<Link>
+        get() = linkMap.values.toList()
+
     // Events forwarded from all nodes.
     private val sink: Sinks.Many<ClientEvent<*>> = Sinks.many().multicast().onBackpressureBuffer()
     val flux: Flux<ClientEvent<*>> = sink.asFlux()
@@ -70,6 +75,9 @@ class LavalinkClient(val userId: Long) : Closeable, Disposable {
         return node
     }
 
+    /**
+     * Remove a node by its [name].
+     */
     fun removeNode(name: String): Boolean {
         val node = nodes.firstOrNull { it.name == name }
 
@@ -80,6 +88,9 @@ class LavalinkClient(val userId: Long) : Closeable, Disposable {
         return removeNode(node)
     }
 
+    /**
+     * Disconnect and remove a node the client.
+     */
     fun removeNode(node: LavalinkNode): Boolean {
         if (node !in internalNodes) {
             return false
@@ -100,19 +111,19 @@ class LavalinkClient(val userId: Long) : Closeable, Disposable {
      */
     @JvmOverloads
     fun getLink(guildId: Long, region: VoiceRegion? = null): Link {
-        if (guildId !in links) {
+        if (!linkMap.containsKey(guildId)) {
             val bestNode = loadBalancer.selectNode(region)
-            links[guildId] = Link(guildId, bestNode)
+            linkMap[guildId] = Link(guildId, bestNode)
         }
 
-        return links[guildId]!!
+        return linkMap[guildId]!!
     }
 
     /**
      * Returns a [Link] if it exists in the cache.
      * If we select a link for voice updates, we don't know the region yet.
      */
-    fun getLinkIfCached(guildId: Long): Link? = links[guildId]
+    fun getLinkIfCached(guildId: Long): Link? = linkMap[guildId]
 
     internal fun onNodeDisconnected(node: LavalinkNode) {
         // Don't do anything if we are shutting down.
@@ -121,13 +132,13 @@ class LavalinkClient(val userId: Long) : Closeable, Disposable {
         }
 
         if (nodes.size == 1) {
-            links.forEach { (_, link) ->
+            linkMap.forEach { (_, link) ->
                 link.state = LinkState.DISCONNECTED
             }
             return
         }
 
-        links.forEach { (_, link) ->
+        linkMap.forEach { (_, link) ->
             if (link.node == node)  {
                 link.transferNode(loadBalancer.selectNode(region = null))
             }