Example test for Frozen Bitmap fault when using Frozen Bitmaps as regular/mutable bitmaps with a read-only buffer #362
Conversation
| } | ||
|
|
||
| func getBytesAsMMap(t *testing.T, startingBytes []byte) []byte { | ||
| os.WriteFile("data", startingBytes, 0777) |
There was a problem hiding this comment.
Surely, there is some needed error handling here?
Note that os.WriteFile is go 1.16. I think you want ioutil.WriteFile for portability.
| primary := getBitmap(t, testCase, startingBitmap) | ||
| assert.True(t, startingBitmap.Equals(primary)) | ||
| clone := primary.Clone() | ||
| primary.Xor(clone) |
There was a problem hiding this comment.
You are modifying, in-place, the frozen view.
There was a problem hiding this comment.
Please consider doing
I would do
newprimary := Xor(primary, clone)
| if testCase.shouldPanic { | ||
| assert.Panics(t, func() { | ||
| debug.SetPanicOnFault(true) | ||
| primary.Xor(clone) |
There was a problem hiding this comment.
You are, again, modifying the frozen view.
There was a problem hiding this comment.
I would do
newprimary := Xor(primary, clone)
I am not sure why you want to mutate the frozen view.
| fileinfo, err := file.Stat() | ||
| require.NoError(t, err) | ||
|
|
||
| bytes, err := unix.Mmap(int(file.Fd()), 0, int(fileinfo.Size()), |
There was a problem hiding this comment.
There is a ressource leak around it, surely.
lemire
changed the title
|
@Oppen Could you take a look? Users are reminded that the frozen support in roaring is experimental. It has minimal testing, and there are no tests with mutation over frozen bitmaps. The frozen format was designed for immutable bitmaps (that you just access without modifying). Using frozen bitmaps as regular bitmaps is an extension. |
|
This PR cannot be merged. I converted it to a draft. |
| require.NoError(t, err) | ||
|
|
||
| bytes, err := unix.Mmap(int(file.Fd()), 0, int(fileinfo.Size()), | ||
| unix.PROT_READ, unix.MAP_PRIVATE) |
There was a problem hiding this comment.
PROT_READ means that the data can be read, it cannot be written to.
lemire
changed the title
|
@jacksonrnewhouse How sure are you that the byte array you get from the memory map is never written to when you mutate the bitmap? Your |
|
|
||
| func getBytesAsMMap(t *testing.T, startingBytes []byte) []byte { | ||
| os.WriteFile("data", startingBytes, 0777) | ||
| file, err := os.OpenFile("data", os.O_RDONLY, 0) |
| fileinfo, err := file.Stat() | ||
| require.NoError(t, err) | ||
|
|
||
| bytes, err := unix.Mmap(int(file.Fd()), 0, int(fileinfo.Size()), |
There was a problem hiding this comment.
bytes has to be immutable, it cannot be written to.
|
As @lemire pointed out, frozen bitmaps are not meant to be modified. The name attempts to make that clear. It could maybe handle that better or behave as CoW, but that's arguably a bad idea, as you'd potentially be duplicating memory use and inducing a leak. The idea of frozen bitmaps is to have an optimized version of read only bitmaps (in particular one that is compatible with CRoaring). I'll look into it with more detail at night. |
This is a test that should not pass but does, as it asserts a panic exactly when FrozenBitmaps and MMap is used. @a392n328 helped me diagnose these issues.