github.com/shogo82148/std@v1.22.1-0.20240327122250-4e474527810c/internal/trace/v2/oldtrace.go

// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This file implements conversion from old (Go 1.11–Go 1.21) traces to the Go
// 1.22 format.
//
// Most events have direct equivalents in 1.22, at worst requiring arguments to
// be reordered. Some events, such as GoWaiting need to look ahead for follow-up
// events to determine the correct translation. GoSyscall, which is an
// instantaneous event, gets turned into a 1 ns long pair of
// GoSyscallStart+GoSyscallEnd, unless we observe a GoSysBlock, in which case we
// emit a GoSyscallStart+GoSyscallEndBlocked pair with the correct duration
// (i.e. starting at the original GoSyscall).
//
// The resulting trace treats the old trace as a single, large generation,
// sharing a single evTable for all events.
//
// We use a new (compared to what was used for 'go tool trace' in earlier
// versions of Go) parser for old traces that is optimized for speed, low memory
// usage, and minimal GC pressure. It allocates events in batches so that even
// though we have to load the entire trace into memory, the conversion process
// shouldn't result in a doubling of memory usage, even if all converted events
// are kept alive, as we free batches once we're done with them.
//
// The conversion process is lossless.

package trace