Default concurrent download count to #CPUS-1.

CHANGELOG.md

@@ -8,6 +8,9 @@
 * When a custom JVM is installed, old JVM files will be deleted prior to unpacking the new JVM. Via
   PR#170.
 
+* Number of concurrent downloads now defaults to num-cores minus one. Though downloads are I/O
+  bound rather than CPU bound, this still turns out to be a decent default.
+
 ## 1.8.2 - Nov 27, 2018
 
 * Fixed a data corruption bug introduced at last minute into 1.8.1 release. Oops.

core/src/main/java/com/threerings/getdown/data/Application.java

@@ -717,7 +717,8 @@ public class Application
         _codeCacheRetentionDays = config.getInt("code_cache_retention_days", 7);
 
         // maximum simultaneous downloads
-        _maxConcDownloads = Math.max(1, config.getInt("max_concurrent_downloads", 2));
+        _maxConcDownloads = Math.max(1, config.getInt("max_concurrent_downloads",
+                                                      SysProps.threadPoolSize()));
 
         // parse and return our application config
         UpdateInterface ui = new UpdateInterface(config);