Wrap deps tasks in a lock

lib/mix/lib/mix/project.ex

@@ -899,6 +899,20 @@ defmodule Mix.Project do
     Mix.Lock.with_lock(build_path, fun, on_taken: on_taken)
   end
 
+  @doc false
+  def with_deps_lock(config \\ config(), fun) do
+    # We wrap operations on the deps directory and on mix.lock to
+    # avoid write conflicts.
+
+    deps_path = deps_path(config)
+
+    on_taken = fn os_pid ->
+      Mix.shell().info("Waiting for lock on the deps directory (held by process #{os_pid})")
+    end
+
+    Mix.Lock.with_lock(deps_path, fun, on_taken: on_taken)
+  end
+
   # Loads mix.exs in the current directory or loads the project from the
   # mixfile cache and pushes the project onto the project stack.
   defp load_project(app, post_config) do

lib/mix/lib/mix/tasks/clean.ex

@@ -30,6 +30,12 @@ defmodule Mix.Tasks.Clean do
 
     {opts, _, _} = OptionParser.parse(args, switches: @switches)
 
+    Mix.Project.with_build_lock(fn ->
+      do_run(opts)
+    end)
+  end
+
+  defp do_run(opts) do
     # First, we get the tasks. After that, we clean them.
     # This is to avoid a task cleaning a compiler module.
     tasks =

lib/mix/lib/mix/tasks/deps.clean.ex

@@ -29,6 +29,14 @@ defmodule Mix.Tasks.Deps.Clean do
     Mix.Project.get!()
     {opts, apps} = OptionParser.parse!(args, strict: @switches)
 
+    Mix.Project.with_build_lock(fn ->
+      Mix.Project.with_deps_lock(fn ->
+        do_run(args, opts, apps)
+      end)
+    end)
+  end
+
+  defp do_run(args, opts, apps) do
     build_path =
       Mix.Project.build_path()
       |> Path.dirname()

lib/mix/lib/mix/tasks/deps.get.ex

@@ -26,6 +26,12 @@ defmodule Mix.Tasks.Deps.Get do
     {opts, _, _} =
       OptionParser.parse(args, switches: [only: :string, target: :string, check_locked: :boolean])
 
+    Mix.Project.with_deps_lock(fn ->
+      do_run(opts)
+    end)
+  end
+
+  defp do_run(opts) do
     fetch_opts =
       for {switch, key} <- [only: :env, target: :target, check_locked: :check_locked],
           value = opts[switch],

lib/mix/lib/mix/tasks/deps.unlock.ex

@@ -27,6 +27,12 @@ defmodule Mix.Tasks.Deps.Unlock do
     Mix.Project.get!()
     {opts, apps, _} = OptionParser.parse(args, switches: @switches)
 
+    Mix.Project.with_deps_lock(fn ->
+      do_run(opts, apps)
+    end)
+  end
+
+  defp do_run(opts, apps) do
     cond do
       opts[:all] ->
         Mix.Dep.Lock.write(%{})

lib/mix/lib/mix/tasks/deps.update.ex

@@ -45,6 +45,12 @@ defmodule Mix.Tasks.Deps.Update do
     {opts, rest, _} =
       OptionParser.parse(args, switches: [all: :boolean, only: :string, target: :string])
 
+    Mix.Project.with_deps_lock(fn ->
+      do_run(opts, rest)
+    end)
+  end
+
+  defp do_run(opts, rest) do
     fetch_opts =
       for {switch, key} <- [only: :env, target: :target],
           value = opts[switch],