Add //pkg/sync:generic_atomicptrmap.

AtomicPtrMap is a generic concurrent map from arbitrary keys to arbitrary
pointer values.

Benchmarks:
name                                                            time/op
StoreDelete/RWMutexMap-12                                        335ns ± 1%
StoreDelete/SyncMap-12                                           705ns ± 3%
StoreDelete/AtomicPtrMap-12                                      287ns ± 4%
StoreDelete/AtomicPtrMapSharded-12                               289ns ± 1%
LoadOrStoreDelete/RWMutexMap-12                                  342ns ± 2%
LoadOrStoreDelete/SyncMap-12                                     662ns ± 2%
LoadOrStoreDelete/AtomicPtrMap-12                                290ns ± 7%
LoadOrStoreDelete/AtomicPtrMapSharded-12                         293ns ± 2%
LookupPositive/RWMutexMap-12                                     101ns ±26%
LookupPositive/SyncMap-12                                        202ns ± 2%
LookupPositive/AtomicPtrMap-12                                  71.1ns ± 2%
LookupPositive/AtomicPtrMapSharded-12                           73.2ns ± 1%
LookupNegative/RWMutexMap-12                                     119ns ± 1%
LookupNegative/SyncMap-12                                        154ns ± 1%
LookupNegative/AtomicPtrMap-12                                  84.7ns ± 3%
LookupNegative/AtomicPtrMapSharded-12                           86.8ns ± 1%
Concurrent/FixedKeys_1PercentWrites_RWMutexMap-12               1.32µs ± 2%
Concurrent/FixedKeys_1PercentWrites_SyncMap-12                  52.7ns ±10%
Concurrent/FixedKeys_1PercentWrites_AtomicPtrMap-12             31.8ns ±20%
Concurrent/FixedKeys_1PercentWrites_AtomicPtrMapSharded-12      24.0ns ±15%
Concurrent/FixedKeys_10PercentWrites_RWMutexMap-12               860ns ± 3%
Concurrent/FixedKeys_10PercentWrites_SyncMap-12                 68.8ns ±20%
Concurrent/FixedKeys_10PercentWrites_AtomicPtrMap-12            98.6ns ± 7%
Concurrent/FixedKeys_10PercentWrites_AtomicPtrMapSharded-12     42.0ns ±25%
Concurrent/FixedKeys_50PercentWrites_RWMutexMap-12              1.17µs ± 3%
Concurrent/FixedKeys_50PercentWrites_SyncMap-12                  136ns ±34%
Concurrent/FixedKeys_50PercentWrites_AtomicPtrMap-12             286ns ± 3%
Concurrent/FixedKeys_50PercentWrites_AtomicPtrMapSharded-12      115ns ±35%
Concurrent/ChangingKeys_1PercentWrites_RWMutexMap-12            1.27µs ± 2%
Concurrent/ChangingKeys_1PercentWrites_SyncMap-12               5.01µs ± 3%
Concurrent/ChangingKeys_1PercentWrites_AtomicPtrMap-12          38.1ns ± 3%
Concurrent/ChangingKeys_1PercentWrites_AtomicPtrMapSharded-12   22.6ns ± 2%
Concurrent/ChangingKeys_10PercentWrites_RWMutexMap-12           1.08µs ± 2%
Concurrent/ChangingKeys_10PercentWrites_SyncMap-12              5.97µs ± 1%
Concurrent/ChangingKeys_10PercentWrites_AtomicPtrMap-12          390ns ± 2%
Concurrent/ChangingKeys_10PercentWrites_AtomicPtrMapSharded-12  93.6ns ± 1%
Concurrent/ChangingKeys_50PercentWrites_RWMutexMap-12           1.77µs ± 2%
Concurrent/ChangingKeys_50PercentWrites_SyncMap-12              8.07µs ± 2%
Concurrent/ChangingKeys_50PercentWrites_AtomicPtrMap-12         1.61µs ± 2%
Concurrent/ChangingKeys_50PercentWrites_AtomicPtrMapSharded-12   386ns ± 1%

Updates #231

PiperOrigin-RevId: 346614776

1 files changed, 49 insertions, 0 deletions

diff --git a/pkg/sync/generic_seqatomic_unsafe.go b/pkg/sync/generic_seqatomic_unsafe.go
new file mode 100644
index 000000000..82b676abf
--- /dev/null
+++ b/pkg/sync/generic_seqatomic_unsafe.go
@@ -0,0 +1,49 @@
+// 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/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.
+		sync.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
+}