Add a persistent bazel server between builds

This feature is toggled on with USE_PERSISTENT_BAZEL, which is off by
default. Those that opt-in will have a bazel server running between
builds (with a 3hr default TTL) which will greatly improve analysis on
subsequent builds. (As Bazel maintains a cache of analysis results).

Bug: 266983462
Test: Manual `m nothing` runs (timing with and without the feature)
Test: New integration test
Test: Presubmits
Change-Id: I3af4948baa0c490e9b87c48ffdbe9f67732586c7

android/bazel_handler.go

@@ -607,7 +607,7 @@ func NewBazelContext(c *config) (BazelContext, error) {
 	dclaEnabledModules := map[string]bool{}
 	addToStringSet(dclaEnabledModules, dclaMixedBuildsEnabledList)
 	return &mixedBuildBazelContext{
-		bazelRunner:             &builtinBazelRunner{},
+		bazelRunner:             &builtinBazelRunner{c.UseBazelProxy, absolutePath(c.outDir)},
 		paths:                   &paths,
 		modulesDefaultToBazel:   c.BuildMode == BazelDevMode,
 		bazelEnabledModules:     enabledModules,
@@ -684,13 +684,35 @@ func (r *mockBazelRunner) issueBazelCommand(bazelCmd *exec.Cmd, _ *metrics.Event
 	return "", "", nil
 }
 
-type builtinBazelRunner struct{}
+type builtinBazelRunner struct {
+	useBazelProxy bool
+	outDir        string
+}
 
 // Issues the given bazel command with given build label and additional flags.
 // Returns (stdout, stderr, error). The first and second return values are strings
 // containing the stdout and stderr of the run command, and an error is returned if
 // the invocation returned an error code.
 func (r *builtinBazelRunner) issueBazelCommand(bazelCmd *exec.Cmd, eventHandler *metrics.EventHandler) (string, string, error) {
+	if r.useBazelProxy {
+		eventHandler.Begin("client_proxy")
+		defer eventHandler.End("client_proxy")
+		proxyClient := bazel.NewProxyClient(r.outDir)
+		// Omit the arg containing the Bazel binary, as that is handled by the proxy
+		// server.
+		bazelFlags := bazelCmd.Args[1:]
+		// TODO(b/270989498): Refactor these functions to not take exec.Cmd, as its
+		// not actually executed for client proxying.
+		resp, err := proxyClient.IssueCommand(bazel.CmdRequest{bazelFlags, bazelCmd.Env})
+
+		if err != nil {
+			return "", "", err
+		}
+		if len(resp.ErrorString) > 0 {
+			return "", "", fmt.Errorf(resp.ErrorString)
+		}
+		return resp.Stdout, resp.Stderr, nil
+	} else {
 		eventHandler.Begin("bazel command")
 		defer eventHandler.End("bazel command")
 		stderr := &bytes.Buffer{}
@@ -702,6 +724,7 @@ func (r *builtinBazelRunner) issueBazelCommand(bazelCmd *exec.Cmd, eventHandler
 		} else {
 			return string(output), string(stderr.Bytes()), nil
 		}
+	}
 }
 
 func (r *builtinBazelRunner) createBazelCommand(config Config, paths *bazelPaths, runName bazel.RunName, command bazelCommand,

android/config.go

@@ -87,6 +87,8 @@ type CmdArgs struct {
 	BazelModeDev             bool
 	BazelModeStaging         bool
 	BazelForceEnabledModules string
+
+	UseBazelProxy bool
 }
 
 // Build modes that soong_build can run as.
@@ -251,6 +253,10 @@ type config struct {
 	// specified modules. They are passed via the command-line flag
 	// "--bazel-force-enabled-modules"
 	bazelForceEnabledModules map[string]struct{}
+
+	// If true, for any requests to Bazel, communicate with a Bazel proxy using
+	// unix sockets, instead of spawning Bazel as a subprocess.
+	UseBazelProxy bool
 }
 
 type deviceConfig struct {
@@ -442,6 +448,8 @@ func NewConfig(cmdArgs CmdArgs, availableEnv map[string]string) (Config, error)
 		mixedBuildDisabledModules: make(map[string]struct{}),
 		mixedBuildEnabledModules:  make(map[string]struct{}),
 		bazelForceEnabledModules:  make(map[string]struct{}),
+
+		UseBazelProxy: cmdArgs.UseBazelProxy,
 	}
 
 	config.deviceConfig = &deviceConfig{

bazel/Android.bp

@@ -7,6 +7,7 @@ bootstrap_go_package {
     pkgPath: "android/soong/bazel",
     srcs: [
         "aquery.go",
+        "bazel_proxy.go",
         "configurability.go",
         "constants.go",
         "properties.go",

bazel/bazel_proxy.go

@@ -0,0 +1,219 @@
+// Copyright 2023 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 bazel
+
+import (
+	"bytes"
+	"encoding/gob"
+	"fmt"
+	"net"
+	os_lib "os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+// Logs fatal events of ProxyServer.
+type ServerLogger interface {
+	Fatal(v ...interface{})
+	Fatalf(format string, v ...interface{})
+}
+
+// CmdRequest is a request to the Bazel Proxy server.
+type CmdRequest struct {
+	// Args to the Bazel command.
+	Argv []string
+	// Environment variables to pass to the Bazel invocation. Strings should be of
+	// the form "KEY=VALUE".
+	Env []string
+}
+
+// CmdResponse is a response from the Bazel Proxy server.
+type CmdResponse struct {
+	Stdout      string
+	Stderr      string
+	ErrorString string
+}
+
+// ProxyClient is a client which can issue Bazel commands to the Bazel
+// proxy server. Requests are issued (and responses received) via a unix socket.
+// See ProxyServer for more details.
+type ProxyClient struct {
+	outDir string
+}
+
+// ProxyServer is a server which runs as a background goroutine. Each
+// request to the server describes a Bazel command which the server should run.
+// The server then issues the Bazel command, and returns a response describing
+// the stdout/stderr of the command.
+// Client-server communication is done via a unix socket under the output
+// directory.
+// The server is intended to circumvent sandboxing for subprocesses of the
+// build. The build orchestrator (soong_ui) can launch a server to exist outside
+// of sandboxing, and sandboxed processes (such as soong_build) can issue
+// bazel commands through this socket tunnel. This allows a sandboxed process
+// to issue bazel requests to a bazel that resides outside of sandbox. This
+// is particularly useful to maintain a persistent Bazel server which lives
+// past the duration of a single build.
+// The ProxyServer will only live as long as soong_ui does; the
+// underlying Bazel server will live past the duration of the build.
+type ProxyServer struct {
+	logger       ServerLogger
+	outDir       string
+	workspaceDir string
+	// The server goroutine will listen on this channel and stop handling requests
+	// once it is written to.
+	done chan struct{}
+}
+
+// NewProxyClient is a constructor for a ProxyClient.
+func NewProxyClient(outDir string) *ProxyClient {
+	return &ProxyClient{
+		outDir: outDir,
+	}
+}
+
+func unixSocketPath(outDir string) string {
+	return filepath.Join(outDir, "bazelsocket.sock")
+}
+
+// IssueCommand issues a request to the Bazel Proxy Server to issue a Bazel
+// request. Returns a response describing the output from the Bazel process
+// (if the Bazel process had an error, then the response will include an error).
+// Returns an error if there was an issue with the connection to the Bazel Proxy
+// server.
+func (b *ProxyClient) IssueCommand(req CmdRequest) (CmdResponse, error) {
+	var resp CmdResponse
+	var err error
+	// Check for connections every 1 second. This is chosen to be a relatively
+	// short timeout, because the proxy server should accept requests quite
+	// quickly.
+	d := net.Dialer{Timeout: 1 * time.Second}
+	var conn net.Conn
+	conn, err = d.Dial("unix", unixSocketPath(b.outDir))
+	if err != nil {
+		return resp, err
+	}
+	defer conn.Close()
+
+	enc := gob.NewEncoder(conn)
+	if err = enc.Encode(req); err != nil {
+		return resp, err
+	}
+	dec := gob.NewDecoder(conn)
+	err = dec.Decode(&resp)
+	return resp, err
+}
+
+// NewProxyServer is a constructor for a ProxyServer.
+func NewProxyServer(logger ServerLogger, outDir string, workspaceDir string) *ProxyServer {
+	return &ProxyServer{
+		logger:       logger,
+		outDir:       outDir,
+		workspaceDir: workspaceDir,
+		done:         make(chan struct{}),
+	}
+}
+
+func (b *ProxyServer) handleRequest(conn net.Conn) error {
+	defer conn.Close()
+
+	dec := gob.NewDecoder(conn)
+	var req CmdRequest
+	if err := dec.Decode(&req); err != nil {
+		return fmt.Errorf("Error decoding request: %s", err)
+	}
+
+	bazelCmd := exec.Command("./build/bazel/bin/bazel", req.Argv...)
+	bazelCmd.Dir = b.workspaceDir
+	bazelCmd.Env = req.Env
+
+	stderr := &bytes.Buffer{}
+	bazelCmd.Stderr = stderr
+	var stdout string
+	var bazelErrString string
+
+	if output, err := bazelCmd.Output(); err != nil {
+		bazelErrString = fmt.Sprintf("bazel command failed: %s\n---command---\n%s\n---env---\n%s\n---stderr---\n%s---",
+			err, bazelCmd, strings.Join(bazelCmd.Env, "\n"), stderr)
+	} else {
+		stdout = string(output)
+	}
+
+	resp := CmdResponse{stdout, string(stderr.Bytes()), bazelErrString}
+	enc := gob.NewEncoder(conn)
+	if err := enc.Encode(&resp); err != nil {
+		return fmt.Errorf("Error encoding response: %s", err)
+	}
+	return nil
+}
+
+func (b *ProxyServer) listenUntilClosed(listener net.Listener) error {
+	for {
+		// Check for connections every 1 second. This is a blocking operation, so
+		// if the server is closed, the goroutine will not fully close until this
+		// deadline is reached. Thus, this deadline is short (but not too short
+		// so that the routine churns).
+		listener.(*net.UnixListener).SetDeadline(time.Now().Add(time.Second))
+		conn, err := listener.Accept()
+
+		select {
+		case <-b.done:
+			return nil
+		default:
+		}
+
+		if err != nil {
+			if opErr, ok := err.(*net.OpError); ok && opErr.Timeout() {
+				// Timeout is normal and expected while waiting for client to establish
+				// a connection.
+				continue
+			} else {
+				b.logger.Fatalf("Listener error: %s", err)
+			}
+		}
+
+		err = b.handleRequest(conn)
+		if err != nil {
+			b.logger.Fatal(err)
+		}
+	}
+}
+
+// Start initializes the server unix socket and (in a separate goroutine)
+// handles requests on the socket until the server is closed. Returns an error
+// if a failure occurs during initialization. Will log any post-initialization
+// errors to the server's logger.
+func (b *ProxyServer) Start() error {
+	unixSocketAddr := unixSocketPath(b.outDir)
+	if err := os_lib.RemoveAll(unixSocketAddr); err != nil {
+		return fmt.Errorf("couldn't remove socket '%s': %s", unixSocketAddr, err)
+	}
+	listener, err := net.Listen("unix", unixSocketAddr)
+
+	if err != nil {
+		return fmt.Errorf("error listening on socket '%s': %s", unixSocketAddr, err)
+	}
+
+	go b.listenUntilClosed(listener)
+	return nil
+}
+
+// Close shuts down the server. This will stop the server from listening for
+// additional requests.
+func (b *ProxyServer) Close() {
+	b.done <- struct{}{}
+}

cmd/soong_build/main.go

@@ -81,6 +81,7 @@ func init() {
 	flag.BoolVar(&cmdlineArgs.BazelMode, "bazel-mode", false, "use bazel for analysis of certain modules")
 	flag.BoolVar(&cmdlineArgs.BazelModeStaging, "bazel-mode-staging", false, "use bazel for analysis of certain near-ready modules")
 	flag.BoolVar(&cmdlineArgs.BazelModeDev, "bazel-mode-dev", false, "use bazel for analysis of a large number of modules (less stable)")
+	flag.BoolVar(&cmdlineArgs.UseBazelProxy, "use-bazel-proxy", false, "communicate with bazel using unix socket proxy instead of spawning subprocesses")
 
 	// Flags that probably shouldn't be flags of soong_build, but we haven't found
 	// the time to remove them yet

tests/persistent_bazel_test.sh

@@ -0,0 +1,83 @@
+#!/bin/bash -eu
+
+# Copyright (C) 2023 The Android Open Source Project
+#
+# 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.
+
+set -o pipefail
+
+source "$(dirname "$0")/lib.sh"
+
+# This test verifies that adding USE_PERSISTENT_BAZEL creates a Bazel process
+# that outlasts the build process.
+# This test should only be run in sandboxed environments (because this test
+# verifies a Bazel process using global process list, and may spawn lingering
+# Bazel processes).
+function test_persistent_bazel {
+  setup
+
+  # Ensure no existing Bazel process.
+  if [[ -e out/bazel/output/server/server.pid.txt ]]; then
+    kill $(cat out/bazel/output/server/server.pid.txt) 2>/dev/null || true
+    if kill -0 $(cat out/bazel/output/server/server.pid.txt) 2>/dev/null ; then
+      fail "Error killing pre-setup bazel"
+    fi
+  fi
+
+  USE_PERSISTENT_BAZEL=1 run_soong nothing
+
+  if ! kill -0 $(cat out/bazel/output/server/server.pid.txt) 2>/dev/null ; then
+    fail "Persistent bazel process expected, but not found after first build"
+  fi
+  BAZEL_PID=$(cat out/bazel/output/server/server.pid.txt)
+
+  USE_PERSISTENT_BAZEL=1 run_soong nothing
+
+  if ! kill -0 $BAZEL_PID 2>/dev/null ; then
+    fail "Bazel pid $BAZEL_PID was killed after second build"
+  fi
+
+  kill $BAZEL_PID 2>/dev/null
+  if ! kill -0 $BAZEL_PID 2>/dev/null ; then
+    fail "Error killing bazel on shutdown"
+  fi
+}
+
+# Verifies that USE_PERSISTENT_BAZEL mode operates as expected in the event
+# that there are Bazel failures.
+function test_bazel_failure {
+  setup
+
+  # Ensure no existing Bazel process.
+  if [[ -e out/bazel/output/server/server.pid.txt ]]; then
+    kill $(cat out/bazel/output/server/server.pid.txt) 2>/dev/null || true
+    if kill -0 $(cat out/bazel/output/server/server.pid.txt) 2>/dev/null ; then
+      fail "Error killing pre-setup bazel"
+    fi
+  fi
+
+  # Introduce a syntax error in a BUILD file which is used in every build
+  # (Note this is a BUILD file which is copied as part of test setup, so this
+  # has no effect on sources outside of this test.
+  rm -rf  build/bazel/rules
+
+  USE_PERSISTENT_BAZEL=1 run_soong nothing 1>out/failurelog.txt 2>&1 && fail "Expected build failure" || true
+
+  if ! grep -sq "'build/bazel/rules' is not a package" out/failurelog.txt ; then
+    fail "Expected error to contain 'build/bazel/rules' is not a package, instead got:\n$(cat out/failurelog.txt)"
+  fi
+
+  kill $(cat out/bazel/output/server/server.pid.txt) 2>/dev/null || true
+}
+
+scan_and_run_tests

tests/run_integration_tests.sh

@@ -7,6 +7,7 @@ TOP="$(readlink -f "$(dirname "$0")"/../../..)"
 "$TOP/build/soong/tests/bootstrap_test.sh"
 "$TOP/build/soong/tests/mixed_mode_test.sh"
 "$TOP/build/soong/tests/bp2build_bazel_test.sh"
+"$TOP/build/soong/tests/persistent_bazel_test.sh"
 "$TOP/build/soong/tests/soong_test.sh"
 "$TOP/build/bazel/ci/rbc_regression_test.sh" aosp_arm64-userdebug
 

ui/build/config.go

@@ -1568,6 +1568,10 @@ func (c *configImpl) IsBazelMixedBuildForceDisabled() bool {
 	return c.Environment().IsEnvTrue("BUILD_BROKEN_DISABLE_BAZEL")
 }
 
+func (c *configImpl) IsPersistentBazelEnabled() bool {
+	return c.Environment().IsEnvTrue("USE_PERSISTENT_BAZEL")
+}
+
 func (c *configImpl) BazelModulesForceEnabledByFlag() string {
 	return c.bazelForceEnabledModules
 }

ui/build/soong.go

@@ -21,6 +21,7 @@ import (
 	"strconv"
 	"strings"
 
+	"android/soong/bazel"
 	"android/soong/ui/metrics"
 	"android/soong/ui/status"
 
@@ -268,6 +269,9 @@ func bootstrapBlueprint(ctx Context, config Config) {
 	if config.bazelStagingMode {
 		mainSoongBuildExtraArgs = append(mainSoongBuildExtraArgs, "--bazel-mode-staging")
 	}
+	if config.IsPersistentBazelEnabled() {
+		mainSoongBuildExtraArgs = append(mainSoongBuildExtraArgs, "--use-bazel-proxy")
+	}
 	if len(config.bazelForceEnabledModules) > 0 {
 		mainSoongBuildExtraArgs = append(mainSoongBuildExtraArgs, "--bazel-force-enabled-modules="+config.bazelForceEnabledModules)
 	}
@@ -497,6 +501,12 @@ func runSoong(ctx Context, config Config) {
 		ctx.BeginTrace(metrics.RunSoong, name)
 		defer ctx.EndTrace()
 
+		if config.IsPersistentBazelEnabled() {
+			bazelProxy := bazel.NewProxyServer(ctx.Logger, config.OutDir(), filepath.Join(config.SoongOutDir(), "workspace"))
+			bazelProxy.Start()
+			defer bazelProxy.Close()
+		}
+
 		fifo := filepath.Join(config.OutDir(), ".ninja_fifo")
 		nr := status.NewNinjaReader(ctx, ctx.Status.StartTool(), fifo)
 		defer nr.Close()