scalar: set the config write-lock timeout to 150ms

By default, Git fails immediately when locking a config file for writing
fails due to an existing lock. With this change, Scalar-registered
repositories will fall back to trying a couple times within a 150ms
timeout.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

Documentation/scalar.adoc

@@ -347,6 +347,9 @@ status.aheadBehind=false::
 	message that can be disabled by disabling the `advice.statusAheadBehind`
 	config.
 
+core.configWriteLockTimeoutMS::
+    Sets a timeout to work gracefully around Git config write contention.
+
 The following settings are different based on which platform is in use:
 
 core.untrackedCache=(true|false)::

scalar.c

@@ -141,6 +141,7 @@ static int set_recommended_config(int reconfigure)
 		{ "commitGraph.changedPaths", "true" },
 		{ "commitGraph.generationVersion", "1" },
 		{ "core.autoCRLF", "false" },
+		{ "core.configWriteLockTimeoutMS", "150" },
 		{ "core.logAllRefUpdates", "true" },
 		{ "core.safeCRLF", "false" },
 		{ "credential.https://dev.azure.com.useHttpPath", "true" },
@@ -228,6 +229,11 @@ static int set_recommended_config(int reconfigure)
  */
 static int toggle_maintenance(int enable)
 {
+	unsigned long ul;
+
+	if (repo_config_get_ulong(the_repository, "core.configWriteLockTimeoutMS", &ul))
+		git_config_push_parameter("core.configWriteLockTimeoutMS=150");
+
 	return run_git("maintenance",
 		       enable ? "start" : "unregister",
 		       enable ? NULL : "--force",
@@ -237,10 +243,14 @@ static int toggle_maintenance(int enable)
 static int add_or_remove_enlistment(int add)
 {
 	int res;
+	unsigned long ul;
 
 	if (!the_repository->worktree)
 		die(_("Scalar enlistments require a worktree"));
 
+	if (repo_config_get_ulong(the_repository, "core.configWriteLockTimeoutMS", &ul))
+		git_config_push_parameter("core.configWriteLockTimeoutMS=150");
+
 	res = run_git("config", "--global", "--get", "--fixed-value",
 		      "scalar.repo", the_repository->worktree, NULL);