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Diffstat (limited to 'ChangeLog')
| -rw-r--r-- | ChangeLog | 56 |
1 files changed, 56 insertions, 0 deletions
@@ -1,3 +1,59 @@ +Fri Aug 26 19:12:08 2011 Hiroshi Nakamura <nahi@ruby-lang.org> + + * variable.c: Make autoload thread-safe. See #921. + + What's the problem? + autoload is thread unsafe. When we define a constant to be + autoloaded, we expect the constant construction is invariant. But + current autoload implementation allows other threads to access the + constant while the first thread is loading a file. + + What's happening inside? + The current implementation uses Qundef as a marker of autoload in + Constant table. Once the first thread find Qundef as a value at + constant lookup, it starts loading a defined feature. Generally a + loaded file overrides the Qundef in Constant table by module/class + declaration at very beginning lines of the file, so other threads + can see the new Module/Class object before feature loading is + finished. It breaks invariant construction. + + How to solve? + To ensure invariant constant construction, we need to override + Qundef with defined Object after the feature loading. For keeping + Qundef in Constant table, I expanded autoload_data struct in + Module to have a slot for keeping the defined object while feature + loading. And changed Module's constant lookup/update logic a + little so that the slot is only visible from the thread which + invokes feature loading. (== the first thread which accessed the + autoload constant) + + Evaluation? + All test passes (bootstrap test, test-all and RubySpec) and added + 8 tests for threading behavior. Extra logics are executed only + when Qundef is found, so no perf drop should happen except + autoloading. + + * variable.c (rb_autoload): Prepare new autoload_data struct. + + * variable.c (rb_autoload_load): Load feature and update Constant + table after feature loading is finished. + + * variable.c (rb_const_get_0): When the fetched constant is under + autoloading, it returns the object only for the thread which starts + autoloading. + + * variable.c (rb_const_defined_0): Ditto. + + * variable.c (rb_const_set): When the specified constant is under + autoloading, it sets the object only for the thread which starts + autoloading. Otherwise, simply overrides Qundef with constant + override warning. + + * vm_insnhelper.c (vm_get_ev_const): Apply same change as + rb_const_get_0 in variable.c. + + * test/ruby/test_autoload.rb: Added tests for threading behavior. + Fri Aug 26 10:10:37 2011 Eric Hodel <drbrain@segment7.net> * lib/rubygems: Update to RubyGems 1.8.10. Fixes security issue in |