Return with an error message if pry is started inside signal handler (#2206)

Mutex#synchronize will throw an error if called from code passed to
Signal.trap. This makes it impossible to start a working Pry session
inside a signal handler.

Currently, calling binding.pry inside signal handling code raises an
exception because Pry uses mutexes to solve various thread-safety
issues.

This commit updates Pry.start to detect whether we'll have the ability
to use Mutex#synchronize. If not, we'll print an error message and
return instead of raising an error.

https://github.com/pry/pry/issues/2191

1 files changed, 25 insertions, 0 deletions

diff --git a/spec/pry_spec.rb b/spec/pry_spec.rb
index 1ea0210d..f5bb0713 100644
--- a/spec/pry_spec.rb
+++ b/spec/pry_spec.rb
@@ -184,6 +184,31 @@ describe Pry do
           .to raise_error SignalException
       end
 
+      describe "inside signal handler" do
+        before do
+          if Pry::Helpers::Platform.jruby?
+            skip "jruby allows mutex usage in signal handlers"
+          end
+
+          if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.0.0")
+            skip "pre-2.0 mri allows mutex usage in signal handlers"
+          end
+
+          trap("USR1") { @str_output = mock_pry }
+        end
+
+        after do
+          trap("USR1") do
+            # do nothing
+          end
+        end
+
+        it "should return with error message" do
+          Process.kill("USR1", Process.pid)
+          expect(@str_output).to match(/Unable to obtain mutex lock/)
+        end
+      end
+
       describe "multi-line input" do
         it "works" do
           expect(mock_pry('x = ', '1 + 4')).to match(/5/)