[GR-40333] Add Process._fork

PullRequest: truffleruby/3691

Author: horakivo

CHANGELOG.md

@@ -89,6 +89,7 @@ Compatibility:
 * Add optional `Hash` argument to `Enumerable#tally` (#2733, @andrykonchin).
 * Update `$LOAD_PATH.resolve_feature_path` to return `nil` instead of raising `LoadError` when feature isn't found (#2733, @andrykonchin).
 * Add `objspace/trace` file (#2733, @andrykonchin).
+* Add `Process._fork` (#2733, @horakivo).
 
 Performance:
 

spec/tags/core/process/_fork_tags.txt

@@ -753,7 +753,7 @@ def self.popen(*args)
     pipe.set_encoding(external, internal)
 
     if cmd == '-'
-      Kernel.fork # will throw an error
+      Process._fork # will throw an error
       raise 'unreachable'
     else
       options = {}

src/main/ruby/truffleruby/core/io.rb

@@ -767,7 +767,7 @@ def at_exit(&block)
   module_function :at_exit
 
   def fork
-    raise NotImplementedError, 'fork is not available'
+    Process._fork
   end
   module_function :fork
   Primitive.method_unimplement method(:fork)

src/main/ruby/truffleruby/core/kernel.rb

@@ -241,10 +241,20 @@ def setsid
   end
 
   def self.fork
-    raise NotImplementedError, 'fork is not available'
+    _fork
   end
   Primitive.method_unimplement method(:fork)
 
+  # An internal API for fork. Do not call this method directly.
+  # Currently, this is called via Kernel.#fork, Process.fork, and IO.popen("-").
+  # This method is not for casual code but for application monitoring
+  # libraries. You can add custom code before and after fork events
+  # by overriding this method.
+  def self._fork
+    raise NotImplementedError, 'fork is not available'
+  end
+  Primitive.method_unimplement method(:_fork)
+
   def times
     Truffle::FFI::MemoryPointer.new(:double, 4) do |ptr|
       ret = Truffle::POSIX.truffleposix_getrusage(ptr)