| commit | 88e2d1c7f9a20e3476dd2cca5112e374c8911eed | [log] [tgz] |
|---|---|---|
| author | Peter Weinberger <pjw@google.com> | Sat Dec 23 07:59:06 2023 -0500 |
| committer | Peter Weinberger <pjw@google.com> | Tue Jan 16 21:27:45 2024 +0000 |
| tree | 44d5585cfff081925d261432efc4e9e82717719a | |
| parent | 76c6b0d9169aaf3a6498afb4ce977524786e15e6 [diff] |
internal/counter: fix file rotation panics
Weekly, the memory-mapped counter file is replaced by a new one.
If this fails, using counters may panic.
This CL fixes the code to avoid the above panics by
setting the counter's file's mapping to nil while there is a danger
that an existing mapping is no longer valid.
The reader can understand the changes using the new TestRotateCounters
at line 99 to see what happens when remapping fails.
1. In the existing code, the current.Lookup at existing line 308 will fault
2. Commenting out that code delays the fault to the c.Inc() at line 106
of rotate_test.go.
3. So the counters have dangling pointers. These have to be reset.
This is done by f.current.Store(nil), and running a cleanup
function at line 313 in the new code. The cleanup function resets
all the counter pointers, and then cleans up the old mapping, if
there is one. (The code to reset the counters cannot be run while
f.mu is locked.)
4. But there is the same problem with counter pointers pointing to the
old mapping even after the file points to the new mapping. The same
solution works, resetting the counter pointer, and then closing
the old mapping. (The old code freed the mapping too soon.)
In both cases (3 and 4), if a counter pointer is used, it will point
to a valid mapping (nil is fine; the increment goes into the
counter's state)
Summary: an old mapping cannot be removed until all the file's
counters point to a new mapping.
The CL also
Fixes some internal documentation,
Fixes a time-related test error that only showed up in Eastern
time evening,
Adds a test showing the life of a counter and testing mapping
failure in file rotation.
Fixes: golang/go#64577
Change-Id: I3e4775fb527e94d8a32505c8d77a131659b0a82a
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/552276
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Peter Weinberger <pjw@google.com>
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