Use Process.spawn, it is enough to implement ChildProcess

* Process.spawn requires only very minimal variants between platforms.
* Remove all other backends, Process.spawn is enough.

.github/workflows/ci.yml

@@ -6,9 +6,11 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu, macos, windows ]
-        ruby: [ 2.6, jruby, truffleruby ]
+        ruby: [ '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', jruby, truffleruby ]
         exclude:
-          - { os: windows, ruby: truffleruby }
+        - { os: windows, ruby: truffleruby }
+        # fails to load rspec: RuntimeError: CRITICAL: RUBYGEMS_ACTIVATION_MONITOR.owned?: before false -> after true
+        - { os: windows, ruby: jruby }
     runs-on: ${{ matrix.os }}-latest
     env:
       CHILDPROCESS_UNSET: should-be-unset

CHANGELOG.md

@@ -1,3 +1,7 @@
+### Version 5.0.0 / TODO
+
+* [#175](https://github.com/enkessler/childprocess/pull/175): Replace all backends by `Process.spawn` for portability, reliability and simplicity.
+
 ### Version 4.1.0 / 2021-06-08
 
 * [#170](https://github.com/enkessler/childprocess/pull/170): Update gem homepage to use `https://`

Gemfile

@@ -5,5 +5,3 @@ gemspec
 
 # Used for local development/testing only
 gem 'rake'
-
-gem 'ffi' if ENV['CHILDPROCESS_POSIX_SPAWN'] == 'true' || Gem.win_platform?

README.md

@@ -73,9 +73,9 @@ begin
   process = ChildProcess.build("sh" , "-c",
                                "for i in {1..3}; do echo $i; sleep 1; done")
   process.io.stdout = w
-  process.start # This results in a fork, inheriting the write end of the pipe.
+  process.start # This results in a subprocess inheriting the write end of the pipe.
 
-  # Close parent's copy of the write end of the pipe so when the (forked) child
+  # Close parent's copy of the write end of the pipe so when the child
   # process closes its write end of the pipe the parent receives EOF when
   # attempting to read from it. If the parent leaves its write end open, it
   # will not detect EOF.
@@ -138,17 +138,6 @@ search.io.stdin.close
 search.wait
 ```
 
-#### Prefer posix_spawn on *nix
-
-If the parent process is using a lot of memory, `fork+exec` can be very expensive. The `posix_spawn()` API removes this overhead.
-
-```ruby
-ChildProcess.posix_spawn = true
-process = ChildProcess.build(*args)
-```
-
-To be able to use this, please make sure that you have the `ffi` gem installed.
-
 ### Ensure entire process tree dies
 
 By default, the child process does not create a new process group. This means there's no guarantee that the entire process tree will die when the child process is killed. To solve this:
@@ -159,6 +148,8 @@ process.leader = true
 process.start
 ```
 
+Note this does not work on Windows.
+
 #### Detach from parent
 
 ```ruby
@@ -195,11 +186,7 @@ ChildProcess.logger = logger
 
 # Implementation
 
-How the process is launched and killed depends on the platform:
-
-* Unix     : `fork + exec` (or `posix_spawn` if enabled)
-* Windows  : `CreateProcess()` and friends
-* JRuby    : `java.lang.{Process,ProcessBuilder}`
+ChildProcess 5+ uses `Process.spawn` from the Ruby core library for maximum portability.
 
 # Note on Patches/Pull Requests
 

lib/childprocess.rb

@@ -2,6 +2,7 @@
 require 'childprocess/errors'
 require 'childprocess/abstract_process'
 require 'childprocess/abstract_io'
+require 'childprocess/process_spawn_process'
 require "fcntl"
 require 'logger'
 
@@ -15,13 +16,7 @@ class << self
     def new(*args)
       case os
       when :macosx, :linux, :solaris, :bsd, :cygwin, :aix
-        if jruby? && !posix_spawn_chosen_explicitly?
-          JRuby::Process.new(args)
-        elsif posix_spawn?
-          Unix::PosixSpawnProcess.new(args)
-        else
-          Unix::ForkExecProcess.new(*args)
-        end
+        Unix::Process.new(*args)
       when :windows
         Windows::Process.new(*args)
       else
@@ -40,13 +35,7 @@ def logger
     end
 
     def platform
-      if RUBY_PLATFORM == "java"
-        :jruby
-      elsif defined?(RUBY_ENGINE) && RUBY_ENGINE == "ironruby"
-        :ironruby
-      else
-        os
-      end
+      os
     end
 
     def platform_name
@@ -62,7 +51,7 @@ def linux?
     end
 
     def jruby?
-      platform == :jruby
+      RUBY_ENGINE == 'jruby'
     end
 
     def windows?
@@ -74,27 +63,6 @@ def posix_spawn_chosen_explicitly?
     end
 
     def posix_spawn?
-      enabled = posix_spawn_chosen_explicitly? || !Process.respond_to?(:fork)
-      return false unless enabled
-
-      begin
-        require 'ffi'
-      rescue LoadError
-        raise ChildProcess::MissingFFIError
-      end
-
-      begin
-        require "childprocess/unix/platform/#{ChildProcess.platform_name}"
-      rescue LoadError
-        raise ChildProcess::MissingPlatformError
-      end
-
-      require "childprocess/unix/lib"
-      require 'childprocess/unix/posix_spawn_process'
-
-      true
-    rescue ChildProcess::MissingPlatformError => ex
-      warn_once ex.message
       false
     end
 
@@ -107,6 +75,8 @@ def posix_spawn=(bool)
     end
 
     def os
+      return :windows if ENV['FAKE_WINDOWS'] == 'true'
+
       @os ||= (
         require "rbconfig"
         host_os = RbConfig::CONFIG['host_os'].downcase
@@ -162,17 +132,6 @@ def arch
     def close_on_exec(file)
       if file.respond_to?(:close_on_exec=)
         file.close_on_exec = true
-      elsif file.respond_to?(:fcntl) && defined?(Fcntl::FD_CLOEXEC)
-        file.fcntl Fcntl::F_SETFD, Fcntl::FD_CLOEXEC
-
-        if jruby? && posix_spawn?
-          # on JRuby, the fcntl call above apparently isn't enough when
-          # we're launching the process through posix_spawn.
-          fileno = JRuby.posix_fileno_for(file)
-          Unix::Lib.fcntl fileno, Fcntl::F_SETFD, Fcntl::FD_CLOEXEC
-        end
-      elsif windows?
-        Windows::Lib.dont_inherit file
       else
         raise Error, "not sure how to set close-on-exec for #{file.inspect} on #{platform_name.inspect}"
       end
@@ -207,8 +166,8 @@ def is_64_bit?
   end # class << self
 end # ChildProcess
 
-require 'jruby' if ChildProcess.jruby?
-
-require 'childprocess/unix'    if ChildProcess.unix?
-require 'childprocess/windows' if ChildProcess.windows?
-require 'childprocess/jruby'   if ChildProcess.jruby?
+if ChildProcess.windows?
+  require 'childprocess/windows'
+else
+  require 'childprocess/unix'
+end

lib/childprocess/abstract_process.rb

@@ -28,7 +28,9 @@ class AbstractProcess
     # Set this to true to make the child process the leader of a new process group
     #
     # This can be used to make sure that all grandchildren are killed
-    # when the child process dies.
+    # when the child process dies on non-Windows.
+    #
+    # Note that grandchildren are not killed on Windows even when the process is the leader of a new process group.
     #
     attr_accessor :leader
 

lib/childprocess/errors.rb

@@ -13,25 +13,4 @@ class InvalidEnvironmentVariable < Error
 
   class LaunchError < Error
   end
-
-  class MissingFFIError < Error
-    def initialize
-      message = "FFI is a required pre-requisite for Windows or posix_spawn support in the ChildProcess gem. " +
-                "Ensure the `ffi` gem is installed. " +
-                "If you believe this is an error, please file a bug at http://github.com/enkessler/childprocess/issues"
-
-      super(message)
-    end
-
-  end
-
-  class MissingPlatformError < Error
-    def initialize
-      message = "posix_spawn is not yet supported on #{ChildProcess.platform_name} (#{RUBY_PLATFORM}), falling back to default implementation. " +
-                "If you believe this is an error, please file a bug at http://github.com/enkessler/childprocess/issues"
-
-      super(message)
-    end
-
-  end
 end