Add TotalRAM detection

Colin originally wrote this for the highmem pool:

https://android-review.googlesource.com/c/platform/build/soong/+/1168271

But while that's a larger change, this is useful to just be in the logs,
and for use in multiproduct_kati to better limit the number of
concurrent jobs.

Test: check soong.log on linux and mac
Change-Id: I0518d303a220d775f8d78dba9f660b2954e68e3e

ui/build/Android.bp

@@ -66,11 +66,13 @@ bootstrap_go_package {
     ],
     darwin: {
         srcs: [
+            "config_darwin.go",
             "sandbox_darwin.go",
         ],
     },
     linux: {
         srcs: [
+            "config_linux.go",
             "sandbox_linux.go",
         ],
     },

ui/build/build.go

@@ -137,6 +137,7 @@ func help(ctx Context, config Config, what int) {
 func Build(ctx Context, config Config, what int) {
 	ctx.Verboseln("Starting build with args:", config.Arguments())
 	ctx.Verboseln("Environment:", config.Environment().Environ())
+	ctx.Verbosef("Total RAM: %dGB", config.TotalRAM()/1024/1024/1024)
 
 	if config.SkipMake() {
 		ctx.Verboseln("Skipping Make/Kati as requested")

ui/build/config.go

@@ -50,6 +50,9 @@ type configImpl struct {
 	targetDevice    string
 	targetDeviceDir string
 
+	// Autodetected
+	totalRAM uint64
+
 	pdkBuild bool
 
 	brokenDupRules    bool
@@ -96,6 +99,8 @@ func NewConfig(ctx Context, args ...string) Config {
 	ret.parallel = runtime.NumCPU() + 2
 	ret.keepGoing = 1
 
+	ret.totalRAM = detectTotalRAM(ctx)
+
 	ret.parseArgs(ctx, args)
 
 	// Make sure OUT_DIR is set appropriately
@@ -716,6 +721,10 @@ func (c *configImpl) Parallel() int {
 	return c.parallel
 }
 
+func (c *configImpl) TotalRAM() uint64 {
+	return c.totalRAM
+}
+
 func (c *configImpl) UseGoma() bool {
 	if v, ok := c.environ.Get("USE_GOMA"); ok {
 		v = strings.TrimSpace(v)

ui/build/config_darwin.go

@@ -0,0 +1,40 @@
+// Copyright 2019 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package build
+
+import (
+	"encoding/binary"
+	"syscall"
+)
+
+func detectTotalRAM(ctx Context) uint64 {
+	s, err := syscall.Sysctl("hw.memsize")
+	if err != nil {
+		ctx.Printf("Failed to get system memory size: %s")
+		return 0
+	}
+
+	// syscall.Sysctl assumes that the return value is a string and trims the last byte if it is 0.
+	if len(s) == 7 {
+		s += "\x00"
+	}
+
+	if len(s) != 8 {
+		ctx.Printf("Failed to get system memory size, returned %d bytes, 8", len(s))
+		return 0
+	}
+
+	return binary.LittleEndian.Uint64([]byte(s))
+}

ui/build/config_linux.go

@@ -0,0 +1,28 @@
+// Copyright 2019 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package build
+
+import "syscall"
+
+func detectTotalRAM(ctx Context) uint64 {
+	var info syscall.Sysinfo_t
+	err := syscall.Sysinfo(&info)
+	if err != nil {
+		ctx.Printf("Failed to get system memory size: %s")
+		return 0
+	}
+	memBytes := uint64(info.Totalram) * uint64(info.Unit)
+	return memBytes
+}