tree d70a048d9d155d3cd41827e9f29f07c8857ca1e3
parent 6497b74122ead111777e0d0de052e9a638b0b8da
author Mike Burrows <m3b@google.com> 1466111558 -0700
committer Mike Burrows <m3b@google.com> 1466111558 -0700

v.io/v23/context: add optional SetFinalizer to find context.CancelFunc leaks.

The change adds a layer of indirection between v.io/v23/context's
CancelFunc functions, and the cancelState calls, and uses
runtime.SetFinalizer() on them to find leaks in which someone
created a cancellable/deadline context, but drops the CancelFunc
on the floor without calling it.

To use, set the environment variable VCONTEXT_LEAK_CHECK to
a file name, and run the Vanadium programme.
Stack traces are appended to the file.

For example:
        VCONTEXT_LEAK_CHECK=/tmp/leak.output jiri test run vanadium-go-test > /tmp/test.output 2>&1

If the environment variable is not set, the level of indirection is not used,
so performance should not be greatly affected in that case.
The change adds a set of benchmarks to verify this.

Before:
BenchmarkWithCancel-12   2000000               739 ns/op             280 B/op          6 allocs/op
BenchmarkWithTimeout-12  1000000              1684 ns/op             496 B/op         11 allocs/op
BenchmarkWithValue-12    5000000               267 ns/op             112 B/op          3 allocs/op

After, without leak detection:
BenchmarkWithCancel-12   2000000               695 ns/op             280 B/op          5 allocs/op
BenchmarkWithTimeout-12  1000000              1803 ns/op             512 B/op         10 allocs/op
BenchmarkWithValue-12   10000000               261 ns/op             112 B/op          3 allocs/op

After, with leak detection:
BenchmarkWithCancel-12    500000              2237 ns/op             488 B/op          7 allocs/op
BenchmarkWithTimeout-12  1000000              3373 ns/op             720 B/op         12 allocs/op
BenchmarkWithValue-12    5000000               272 ns/op             112 B/op          3 allocs/op

Change-Id: Ia24c671ac8996916197fb693c928cbc8dac6ae86