5 files changed, 43 insertions, 57 deletions
diff --git a/lib/rubygems/ext/builder.rb b/lib/rubygems/ext/builder.rb
index afc8cb0ee4..f6de6a50d7 100644
--- a/lib/rubygems/ext/builder.rb
+++ b/lib/rubygems/ext/builder.rb
@@ -10,14 +10,6 @@ require_relative '../user_interaction'
 class Gem::Ext::Builder
   include Gem::UserInteraction
 
-  ##
-  # The builder shells-out to run various commands after changing the
-  # directory.  This means multiple installations cannot be allowed to build
-  # extensions in parallel as they may change each other's directories leading
-  # to broken extensions or failed installations.
-
-  CHDIR_MUTEX = Mutex.new # :nodoc:
-
   attr_accessor :build_args # :nodoc:
 
   def self.class_name
@@ -25,8 +17,8 @@ class Gem::Ext::Builder
     $1.downcase
   end
 
-  def self.make(dest_path, results)
-    unless File.exist? 'Makefile'
+  def self.make(dest_path, results, make_dir = Dir.pwd)
+    unless File.exist? File.join(make_dir, 'Makefile')
       raise Gem::InstallError, 'Makefile not found'
     end
 
@@ -44,32 +36,32 @@ class Gem::Ext::Builder
       cmd = [
         make_program,
         destdir,
-        target
+        target,
       ].join(' ').rstrip
       begin
-        run(cmd, results, "make #{target}".rstrip)
+        run(cmd, results, "make #{target}".rstrip, make_dir)
       rescue Gem::InstallError
         raise unless target == 'clean' # ignore clean failure
       end
     end
   end
 
-  def self.run(command, results, command_name = nil)
+  def self.run(command, results, command_name = nil, dir = Dir.pwd)
     verbose = Gem.configuration.really_verbose
 
     begin
       rubygems_gemdeps, ENV['RUBYGEMS_GEMDEPS'] = ENV['RUBYGEMS_GEMDEPS'], nil
       if verbose
-        puts("current directory: #{Dir.pwd}")
+        puts("current directory: #{dir}")
         p(command)
       end
-      results << "current directory: #{Dir.pwd}"
+      results << "current directory: #{dir}"
       results << (command.respond_to?(:shelljoin) ? command.shelljoin : command)
 
       require "open3"
       # Set $SOURCE_DATE_EPOCH for the subprocess.
       env = {'SOURCE_DATE_EPOCH' => Gem.source_date_epoch_string}
-      output, status = Open3.capture2e(env, *command)
+      output, status = Open3.capture2e(env, *command, :chdir => dir)
       if verbose
         puts output
       else
@@ -161,22 +153,10 @@ EOF
     begin
       FileUtils.mkdir_p dest_path
 
-      CHDIR_MUTEX.synchronize do
-        pwd = Dir.getwd
-        Dir.chdir extension_dir
-        begin
-          results = builder.build(extension, dest_path,
-                                  results, @build_args, lib_dir)
-
-          verbose { results.join("\n") }
-        ensure
-          begin
-            Dir.chdir pwd
-          rescue SystemCallError
-            Dir.chdir dest_path
-          end
-        end
-      end
+      results = builder.build(extension, dest_path,
+                              results, @build_args, lib_dir, extension_dir)
+
+      verbose { results.join("\n") }
 
       write_gem_make_out results.join "\n"
     rescue => e
@@ -201,6 +181,7 @@ EOF
 
     dest_path = @spec.extension_dir
 
+    require "fileutils"
     FileUtils.rm_f @spec.gem_build_complete_path
 
     @spec.extensions.each do |extension|
diff --git a/lib/rubygems/ext/cmake_builder.rb b/lib/rubygems/ext/cmake_builder.rb
index 519372e742..2efec91f15 100644
--- a/lib/rubygems/ext/cmake_builder.rb
+++ b/lib/rubygems/ext/cmake_builder.rb
@@ -2,15 +2,15 @@
 require_relative '../command'
 
 class Gem::Ext::CmakeBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
-    unless File.exist?('Makefile')
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, cmake_dir=Dir.pwd)
+    unless File.exist?(File.join(cmake_dir, 'Makefile'))
       cmd = "cmake . -DCMAKE_INSTALL_PREFIX=#{dest_path}"
       cmd << " #{Gem::Command.build_args.join ' '}" unless Gem::Command.build_args.empty?
 
-      run cmd, results
+      run cmd, results, class_name, cmake_dir
     end
 
-    make dest_path, results
+    make dest_path, results, cmake_dir
 
     results
   end
diff --git a/lib/rubygems/ext/configure_builder.rb b/lib/rubygems/ext/configure_builder.rb
index 209e75fe8e..36a758989b 100644
--- a/lib/rubygems/ext/configure_builder.rb
+++ b/lib/rubygems/ext/configure_builder.rb
@@ -6,15 +6,15 @@
 #++
 
 class Gem::Ext::ConfigureBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
-    unless File.exist?('Makefile')
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, configure_dir=Dir.pwd)
+    unless File.exist?(File.join(configure_dir, 'Makefile'))
       cmd = "sh ./configure --prefix=#{dest_path}"
       cmd << " #{args.join ' '}" unless args.empty?
 
-      run cmd, results
+      run cmd, results, class_name, configure_dir
     end
 
-    make dest_path, results
+    make dest_path, results, configure_dir
 
     results
   end
diff --git a/lib/rubygems/ext/ext_conf_builder.rb b/lib/rubygems/ext/ext_conf_builder.rb
index 305e1dcfb1..fede270417 100644
--- a/lib/rubygems/ext/ext_conf_builder.rb
+++ b/lib/rubygems/ext/ext_conf_builder.rb
@@ -8,11 +8,11 @@
 require 'shellwords'
 
 class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, extension_dir=Dir.pwd)
     require 'fileutils'
     require 'tempfile'
 
-    tmp_dest = Dir.mktmpdir(".gem.", ".")
+    tmp_dest = Dir.mktmpdir(".gem.", extension_dir)
 
     # Some versions of `mktmpdir` return absolute paths, which will break make
     # if the paths contain spaces. However, on Ruby 1.9.x on Windows, relative
@@ -23,9 +23,9 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
     # spaces do not work.
     #
     # Details: https://github.com/rubygems/rubygems/issues/977#issuecomment-171544940
-    tmp_dest = get_relative_path(tmp_dest)
+    tmp_dest = get_relative_path(tmp_dest, extension_dir)
 
-    Tempfile.open %w[siteconf .rb], "." do |siteconf|
+    Tempfile.open %w[siteconf .rb], extension_dir do |siteconf|
       siteconf.puts "require 'rbconfig'"
       siteconf.puts "dest_path = #{tmp_dest.dump}"
       %w[sitearchdir sitelibdir].each do |dir|
@@ -38,19 +38,22 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
       destdir = ENV["DESTDIR"]
 
       begin
+        # workaround for https://github.com/oracle/truffleruby/issues/2115
+        siteconf_path = RUBY_ENGINE == "truffleruby" ? siteconf.path.dup : siteconf.path
         cmd = Gem.ruby.shellsplit << "-I" << File.expand_path("../../..", __FILE__) <<
-              "-r" << get_relative_path(siteconf.path) << File.basename(extension)
+              "-r" << get_relative_path(siteconf_path, extension_dir) << File.basename(extension)
         cmd.push(*args)
 
         begin
-          run(cmd, results) do |s, r|
-            if File.exist? 'mkmf.log'
+          run(cmd, results, class_name, extension_dir) do |s, r|
+            mkmf_log = File.join(extension_dir, 'mkmf.log')
+            if File.exist? mkmf_log
               unless s.success?
                 r << "To see why this extension failed to compile, please check" \
                   " the mkmf.log which can be found here:\n"
                 r << "  " + File.join(dest_path, 'mkmf.log') + "\n"
               end
-              FileUtils.mv 'mkmf.log', dest_path
+              FileUtils.mv mkmf_log, dest_path
             end
           end
           siteconf.unlink
@@ -58,18 +61,20 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
 
         ENV["DESTDIR"] = nil
 
-        make dest_path, results
+        make dest_path, results, extension_dir
 
         if tmp_dest
+          full_tmp_dest = File.join(extension_dir, tmp_dest)
+
           # TODO remove in RubyGems 3
           if Gem.install_extension_in_lib and lib_dir
             FileUtils.mkdir_p lib_dir
-            entries = Dir.entries(tmp_dest) - %w[. ..]
-            entries = entries.map {|entry| File.join tmp_dest, entry }
+            entries = Dir.entries(full_tmp_dest) - %w[. ..]
+            entries = entries.map {|entry| File.join full_tmp_dest, entry }
             FileUtils.cp_r entries, lib_dir, :remove_destination => true
           end
 
-          FileUtils::Entry_.new(tmp_dest).traverse do |ent|
+          FileUtils::Entry_.new(full_tmp_dest).traverse do |ent|
             destent = ent.class.new(dest_path, ent.rel)
             destent.exist? or FileUtils.mv(ent.path, destent.path)
           end
@@ -87,8 +92,8 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
 
   private
 
-  def self.get_relative_path(path)
-    path[0..Dir.pwd.length - 1] = '.' if path.start_with?(Dir.pwd)
+  def self.get_relative_path(path, base)
+    path[0..base.length - 1] = '.' if path.start_with?(base)
     path
   end
 end
diff --git a/lib/rubygems/ext/rake_builder.rb b/lib/rubygems/ext/rake_builder.rb
index 53507090fe..34c3922f2f 100644
--- a/lib/rubygems/ext/rake_builder.rb
+++ b/lib/rubygems/ext/rake_builder.rb
@@ -8,9 +8,9 @@
 require "shellwords"
 
 class Gem::Ext::RakeBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, extension_dir=Dir.pwd)
     if File.basename(extension) =~ /mkrf_conf/i
-      run([Gem.ruby, File.basename(extension), *args], results)
+      run([Gem.ruby, File.basename(extension), *args], results, class_name, extension_dir)
     end
 
     rake = ENV['rake']
@@ -26,7 +26,7 @@ class Gem::Ext::RakeBuilder < Gem::Ext::Builder
     end
 
     rake_args = ["RUBYARCHDIR=#{dest_path}", "RUBYLIBDIR=#{dest_path}", *args]
-    run(rake + rake_args, results)
+    run(rake + rake_args, results, class_name, extension_dir)
 
     results
   end