go/common: Make DefaultSink thread-safe #12485
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Changelog[uncommitted] (2023-03-24)Bug Fixes
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This was referenced Mar 23, 2023
Frassle
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diag.DefaultSink is not safe for concurrent use. Whether we use it with os.File or with a bytes.Buffer, both targets do not synchronize their writes, so this leaves room for interleaving of messages. Making diag.DefaultSink thread-safe is generally desirable, but is also a requirement for #12438 so that it can run upgrades concurrently and print warnings as tasks fail. This makes the result of DefaultSink thread-safe by adding a mutex around the targeted stdout and stderr. Note: As a special case, when stdout and stderr are the same we want to use the same mutex for them. This matches the behavior of [os/exec.Cmd][1] // If Stdout and Stderr are the same writer, and have a type that can // be compared with ==, at most one goroutine at a time will call Write. Stdout io.Writer Stderr io.Writer [1]: https://pkg.go.dev/os/exec#Cmd A writer implementation can be anything, and is not guaranteed to be comparable with `==`. When that happens, the `==` will panic. To prevent regressions, we have to handle that case and treat uncomparable writers as different. This is also similar to how os/exec does it: https://cs.opensource.google/go/go/+/refs/tags/go1.20.2:src/os/exec/exec.go;l=475
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12485: go/common: Make DefaultSink thread-safe r=abhinav a=abhinav diag.DefaultSink is not safe for concurrent use. Whether we use it with os.File or with a bytes.Buffer, both targets do not synchronize their writes, so this leaves room for interleaving of messages. Making diag.DefaultSink thread-safe is generally desirable, but is also a requirement for #12438 so that it can run upgrades concurrently and print warnings as tasks fail. This makes the result of DefaultSink thread-safe by adding a mutex around the targeted stdout and stderr. Note: As a special case, when stdout and stderr are the same we want to use the same mutex for them. This matches the behavior of [os/exec.Cmd][1] // If Stdout and Stderr are the same writer, and have a type that can // be compared with ==, at most one goroutine at a time will call Write. Stdout io.Writer Stderr io.Writer [1]: https://pkg.go.dev/os/exec#Cmd A writer implementation can be anything, and is not guaranteed to be comparable with `==`. When that happens, the `==` will panic. To prevent regressions, we have to handle that case and treat uncomparable writers as different. This is also similar to how os/exec does it: https://cs.opensource.google/go/go/+/refs/tags/go1.20.2:src/os/exec/exec.go;l=475 Co-authored-by: Abhinav Gupta <abhinav@pulumi.com>
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12485: go/common: Make DefaultSink thread-safe r=abhinav a=abhinav diag.DefaultSink is not safe for concurrent use. Whether we use it with os.File or with a bytes.Buffer, both targets do not synchronize their writes, so this leaves room for interleaving of messages. Making diag.DefaultSink thread-safe is generally desirable, but is also a requirement for #12438 so that it can run upgrades concurrently and print warnings as tasks fail. This makes the result of DefaultSink thread-safe by adding a mutex around the targeted stdout and stderr. Note: As a special case, when stdout and stderr are the same we want to use the same mutex for them. This matches the behavior of [os/exec.Cmd][1] // If Stdout and Stderr are the same writer, and have a type that can // be compared with ==, at most one goroutine at a time will call Write. Stdout io.Writer Stderr io.Writer [1]: https://pkg.go.dev/os/exec#Cmd A writer implementation can be anything, and is not guaranteed to be comparable with `==`. When that happens, the `==` will panic. To prevent regressions, we have to handle that case and treat uncomparable writers as different. This is also similar to how os/exec does it: https://cs.opensource.google/go/go/+/refs/tags/go1.20.2:src/os/exec/exec.go;l=475 Co-authored-by: Abhinav Gupta <abhinav@pulumi.com>
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diag.DefaultSink is not safe for concurrent use.
Whether we use it with os.File or with a bytes.Buffer,
both targets do not synchronize their writes,
so this leaves room for interleaving of messages.
Making diag.DefaultSink thread-safe is generally desirable,
but is also a requirement for #12438
so that it can run upgrades concurrently
and print warnings as tasks fail.
This makes the result of DefaultSink thread-safe
by adding a mutex around the targeted stdout and stderr.
Note:
As a special case, when stdout and stderr are the same
we want to use the same mutex for them.
This matches the behavior of os/exec.Cmd
A writer implementation can be anything,
and is not guaranteed to be comparable with
==.When that happens, the
==will panic.To prevent regressions, we have to handle that case
and treat uncomparable writers as different.
This is also similar to how os/exec does it:
https://cs.opensource.google/go/go/+/refs/tags/go1.20.2:src/os/exec/exec.go;l=475