Checkpoint.

- Fix a couple of edge cases while switching between collections.
  - Raise error if attempting to switch collections mid-transaction.
  - Add logic for re-entrancy with long-running transactions.
  - Revert to the prior collection if passing a block to #collection.
  - Add a predicate to tell if you're currently within a long-running transaction.
  - Add separate commit/rollback to long-running transactions.

FossilOrigin-Name: 711239e6fc2f25479a26fb54805da1e5db792f97f28a8b5724e0b38eb11cdb07

spec/mdbx/database_spec.rb

@@ -1,4 +1,5 @@
 #!/usr/bin/env rspec -cfd
+# vim: set nosta noet ts=4 sw=4 ft=ruby:
 
 require_relative '../lib/helper'
 
@@ -113,6 +114,12 @@ RSpec.describe( MDBX::Database ) do
 			expect( db['key'] ).to be_truthy
 		end
 
+		it "revert back to the previous collection when used in a block" do
+			expect( db.collection ).to be_nil
+			db.collection( 'bucket' ) { 'no-op' }
+			expect( db.collection ).to be_nil
+		end
+
 		it "can be cleared of contents" do
 			db.collection( 'bucket' )
 			10.times {|i| db[i] = true }

spec/mdbx/stats_spec.rb

@@ -0,0 +1,57 @@
+#!/usr/bin/env rspec -cfd
+# vim: set nosta noet ts=4 sw=4 ft=ruby:
+
+require_relative '../lib/helper'
+
+
+RSpec.fdescribe( MDBX::Database ) do
+
+	let!( :db ) { described_class.open( TEST_DATABASE.to_s, max_readers: 500 ) }
+
+	let( :stats ) { db.statistics }
+
+	after( :each ) do
+		db.close
+	end
+
+	it "returns the configured max_readers" do
+		expect( stats.dig(:environment, :max_readers) ).to be >= 500
+	end
+
+	it "returns compile time flags and options" do
+		build = stats[ :build ]
+		expect( build.keys.size ).to be( 4 )
+		expect( build.keys ).to include( :compiler, :flags, :options, :target )
+		expect( build[:compiler] ).to be_a( String )
+		expect( build[:flags] ).to be_a( String )
+		expect( build[:target] ).to be_a( String )
+		expect( build[:options] ).to be_a( Hash )
+	end
+
+end
+
+
+__END__
+{:environment=>
+  {:pagesize=>4096,
+     :last_txnid=>125,
+     :last_reader_txnid=>125,
+     :maximum_readers=>122,
+     :readers_in_use=>1,
+     :datafile=>
+      {:size_current=>65536,
+	       :pages=>16,
+	       :type=>"dynamic",
+	       :size_lower=>12288,
+	       :size_upper=>1048576,
+	       :growth_step=>65536,
+	       :shrink_threshold=>131072}},
+ :readers=>
+  [{:slot=>0,
+      :pid=>45436,
+      :thread=>34374651904,
+      :txnid=>0,
+      :lag=>0,
+      :bytes_used=>0,
+      :bytes_retired=>0}]}
+}