b25eb8f596
This code represents an attempt at providing reliable tracking of whether any bitmaps still in use have access to a given block of mmapped data, allowing us to unmap the data when nothing is using it anymore. The basic approach is as follows: Each mmap is associated with a new object, called a "generation". A generation reflects a particular instance of a given file being mapped. When a bitmap is built from an mmapped data source, the bitmap is given a pointer to the generation as its Source. When bitmap operations combine containers from other bitmaps, they produce new bitmaps that are tagged with the combined set of sources. When we snapshot a file, or for some other reason wish to remap it, the corresponding bitmap has all its containers updated to use the new storage, and the bitmap's source is changed. However, previously-handed-out containers might still have references to the old storage. Those containers would be in bitmaps with the old source. After a bunch of study of trying to reference-count and track this, I realized: We don't actually need to do that, because we already have something suitable for determining whether anything can reach a given object. It's the garbage collector. So we set a finalizer on the generation object, which handles unmapping. There's additional sanity-checks here to confirm things like "we thought this generation should be expiring", and we track timestamps. We could also have things check whether a given bitmap's source was marked as obsolete "a while ago", but that isn't implemented yet. There's a debug version of this which tracks finalization, creation, and ending timestamps, and has a call to provide diagnostics for this. Identical generation IDs get separated out with random suffixes in this case -- there's sometimes a second or third instance of the same name due to a holder closing and reopening, but this basically only happens in testing. Note that generations are still used even when there's no mmapping, but unless debugging is turned on, they shouldn't propagate much -- we don't consider a generation to be the source of a bitmap unless the bitmap actually mapped things from that generation's mmapped storage, or debugging is on. There's a couple of other, possibly more subtle, changes and bug fixes that got caught by the testing on this: * If a fragment is partially opened and then opening some later part fails, we close the earlier parts before returning the error so we aren't leaving it partially open. * Several operations on segments which were requesting that a frozen copy of a bitmap be created are now actually *replacing* their bitmap with the frozen bitmap, rather than discarding it. * intersectRunRun, if it decides to create an array or bitmap, will yield that container instead of discarding it. And why all of this? Why, so we can actually implement the thing where when a fragment has a valid roaring bitmap, but the ops log is corrupt, we can truncate the corrupt part of the ops log and reopen it. Which I did. When the generationdebug build tag is in use, every generation has a finalizer all the time. When it's not, they only get finalizers when we expect them to be done -- say, when closing a fragment. This is because finalizers appear to be possibly-expensive. There's some logical cleanup to openStorage here, dividing part of its work into applyStorage and importStorage, which have a common case for handling "there's no data in this file". |
||
|---|---|---|
| .. | ||
| testdata | ||
| btree.go | ||
| btree_test.go | ||
| container_stash.go | ||
| containers_btree.go | ||
| containers_slice.go | ||
| containers_test.go | ||
| fuzz_test.go | ||
| fuzzer.go | ||
| generation_debug.go | ||
| generation_nodebug.go | ||
| inst.go | ||
| naive.go | ||
| naive_test.go | ||
| nop_inst.go | ||
| README.md | ||
| roaring.go | ||
| roaring_helpers_test.go | ||
| roaring_internal_test.go | ||
| roaring_nop_paranoia.go | ||
| roaring_nop_sentinel.go | ||
| roaring_nop_stats.go | ||
| roaring_paranoia.go | ||
| roaring_sentinel.go | ||
| roaring_stats.go | ||
| roaring_test.go | ||
| source.go | ||
| unmarshal_binary.go | ||
The Fuzzer
For complete documentation on go-fuzz, please see: https://github.com/dvyukov/go-fuzz
The fuzzer in relation to the roaring package checks the Bitmap.UnmarshalBinary function found in roaring.go. In order to use the fuzzer, you can follow these steps:
cd $GOPATH/src/github.com/pilosa/pilosa/roaring
go-fuzz-build ./
You must now make the workdir/corpus directory. This is achieved by:
mkdir workdir/corpus
The fuzzer needs some input to start the fuzzing with. Copy some sample Pilosa fragments into the workdir/corpus folder. For example:
cp ~/.pilosa/my-index/my-field/views/standard/fragments/0 workdir/corpus
Once you have copied your sample inputs, you are ready to run the fuzzer:
go-fuzz -bin=roaring-fuzz.zip -workdir=workdir -func=FuzzBitmapUnmarshalBinary
Understanding the Fuzzer Output
The fuzzer will output something similar to the follwoing:
2015/04/25 12:39:53 workers: 8, corpus: 124 (12s ago), crashers: 37, restarts: 1/15, execs: 35342 (2941/sec), cover: 403, uptime: 12s
The most important part of the output is the crashers and cover. The crashers records how many combinations were discovered that fail and the cover tells you how much code is being accessed.
For a complete explanation of the output, please see: https://github.com/dvyukov/go-fuzz.
The fuzzer will document the crashers in a folder labeled "crashers." It will record the fragment and the error that was produced in two separate files within this folder. This is the final product.
Happy Fuzzing!