From 12f4118437584c4a0e4738b9dde3e1885cef3de8 Mon Sep 17 00:00:00 2001 From: Tamir Duberstein Date: Tue, 1 Jun 2021 17:45:10 -0700 Subject: Move sync generics to their own packages The presence of multiple packages in a single directory sometimes confuses `go mod`, producing output like: go: downloading gvisor.dev/gvisor v0.0.0-20210601174640-77dc0f5bc94d $GOMODCACHE/gvisor.dev/gvisor@v0.0.0-20210601174640-77dc0f5bc94d/pkg/linewriter/linewriter.go:21:2: found packages sync (aliases.go) and seqatomic (generic_atomicptr_unsafe.go) in $GOMODCACHE/gvisor.dev/gvisor@v0.0.0-20210601174640-77dc0f5bc94d/pkg/sync imports.go:67:2: found packages tcp (accept.go) and rcv (rcv_test.go) in $GOMODCACHE/gvisor.dev/gvisor@v0.0.0-20210601174640-77dc0f5bc94d/pkg/tcpip/transport/tcp PiperOrigin-RevId: 376956213 --- pkg/sync/seqatomic/generic_seqatomic_unsafe.go | 50 ++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 pkg/sync/seqatomic/generic_seqatomic_unsafe.go (limited to 'pkg/sync/seqatomic/generic_seqatomic_unsafe.go') diff --git a/pkg/sync/seqatomic/generic_seqatomic_unsafe.go b/pkg/sync/seqatomic/generic_seqatomic_unsafe.go new file mode 100644 index 000000000..9578c9c52 --- /dev/null +++ b/pkg/sync/seqatomic/generic_seqatomic_unsafe.go @@ -0,0 +1,50 @@ +// Copyright 2019 The gVisor Authors. +// +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Package seqatomic doesn't exist. This file must be instantiated using the +// go_template_instance rule in tools/go_generics/defs.bzl. +package seqatomic + +import ( + "unsafe" + + "gvisor.dev/gvisor/pkg/gohacks" + "gvisor.dev/gvisor/pkg/sync" +) + +// Value is a required type parameter. +type Value struct{} + +// SeqAtomicLoad returns a copy of *ptr, ensuring that the read does not race +// with any writer critical sections in seq. +// +//go:nosplit +func SeqAtomicLoad(seq *sync.SeqCount, ptr *Value) Value { + for { + if val, ok := SeqAtomicTryLoad(seq, seq.BeginRead(), ptr); ok { + return val + } + } +} + +// SeqAtomicTryLoad returns a copy of *ptr while in a reader critical section +// in seq initiated by a call to seq.BeginRead() that returned epoch. If the +// read would race with a writer critical section, SeqAtomicTryLoad returns +// (unspecified, false). +// +//go:nosplit +func SeqAtomicTryLoad(seq *sync.SeqCount, epoch sync.SeqCountEpoch, ptr *Value) (val Value, ok bool) { + if sync.RaceEnabled { + // runtime.RaceDisable() doesn't actually stop the race detector, so it + // can't help us here. Instead, call runtime.memmove directly, which is + // not instrumented by the race detector. + gohacks.Memmove(unsafe.Pointer(&val), unsafe.Pointer(ptr), unsafe.Sizeof(val)) + } else { + // This is ~40% faster for short reads than going through memmove. + val = *ptr + } + ok = seq.ReadOk(epoch) + return +} -- cgit v1.2.3