From 3fbde346ad04a557d519239d8d4f88bc6c8a7333 Mon Sep 17 00:00:00 2001
From: Andreas Gampe <agampe@google.com>
Date: Wed, 12 Jul 2017 19:17:52 -0700
Subject: [PATCH] Zygote: Poll with timeout for pid

Do not use a blocking readInt. Poll for available bytes with a timeout.

(cherry picked from commit cbc421406193308667a38b0bebc16c4064a19e83)

Bug: 63638768
Test: m
Test: cts-tradefed run commandAndExit cts-dev -m CtsWrapWrapDebugTestCases
Change-Id: Ib2131c00aa47dd10bb940d8678bbbfb5a0346ad5
---
 .../android/internal/os/ZygoteConnection.java | 66 ++++++++++++++++---
 1 file changed, 57 insertions(+), 9 deletions(-)

diff --git a/core/java/com/android/internal/os/ZygoteConnection.java b/core/java/com/android/internal/os/ZygoteConnection.java
index 91429a6092885..941ded3af8fe5 100644
--- a/core/java/com/android/internal/os/ZygoteConnection.java
+++ b/core/java/com/android/internal/os/ZygoteConnection.java
@@ -18,6 +18,7 @@ package com.android.internal.os;
 
 import static android.system.OsConstants.F_SETFD;
 import static android.system.OsConstants.O_CLOEXEC;
+import static android.system.OsConstants.POLLIN;
 import static android.system.OsConstants.STDERR_FILENO;
 import static android.system.OsConstants.STDIN_FILENO;
 import static android.system.OsConstants.STDOUT_FILENO;
@@ -31,13 +32,14 @@ import android.os.SystemProperties;
 import android.os.Trace;
 import android.system.ErrnoException;
 import android.system.Os;
+import android.system.StructPollfd;
 import android.util.Log;
 import dalvik.system.VMRuntime;
 import java.io.BufferedReader;
+import java.io.ByteArrayInputStream;
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
 import java.io.FileDescriptor;
-import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
@@ -807,17 +809,63 @@ class ZygoteConnection {
 
         boolean usingWrapper = false;
         if (pipeFd != null && pid > 0) {
-            DataInputStream is = new DataInputStream(new FileInputStream(pipeFd));
             int innerPid = -1;
             try {
-                innerPid = is.readInt();
-            } catch (IOException ex) {
-                Log.w(TAG, "Error reading pid from wrapped process, child may have died", ex);
-            } finally {
-                try {
-                    is.close();
-                } catch (IOException ex) {
+                // Do a busy loop here. We can't guarantee that a failure (and thus an exception
+                // bail) happens in a timely manner.
+                //
+                // We'll wait up to five seconds. This should give enough time for the fork to go
+                // through, but not to trigger the watchdog in the system server.
+                final int SLEEP_IN_MS = 5000;
+                final int BYTES_REQUIRED = 4;  // Bytes in an int.
+
+                StructPollfd fds[] = new StructPollfd[] {
+                        new StructPollfd()
+                };
+
+                byte data[] = new byte[BYTES_REQUIRED];
+
+                int remainingSleepTime = SLEEP_IN_MS;
+                int dataIndex = 0;
+                long startTime = System.nanoTime();
+
+                while (dataIndex < data.length && remainingSleepTime > 0) {
+                    fds[0].fd = pipeFd;
+                    fds[0].events = (short) POLLIN;
+                    fds[0].revents = 0;
+                    fds[0].userData = null;
+
+                    int res = android.system.Os.poll(fds, remainingSleepTime);
+                    long endTime = System.nanoTime();
+                    remainingSleepTime = SLEEP_IN_MS - (int)((endTime - startTime) / 1000000l);
+
+                    if (res > 0) {
+                        if ((fds[0].revents & POLLIN) != 0) {
+                            // Only read one byte, so as not to block.
+                            int readBytes = android.system.Os.read(pipeFd, data, dataIndex, 1);
+                            if (readBytes < 0) {
+                                throw new RuntimeException("Some error");
+                            }
+                            dataIndex += readBytes;
+                        } else {
+                            // Error case. revents should contain one of the error bits.
+                            break;
+                        }
+                    } else if (res == 0) {
+                        Log.w(TAG, "Timed out waiting for child.");
+                    }
                 }
+
+                if (dataIndex == data.length) {
+                    DataInputStream is = new DataInputStream(new ByteArrayInputStream(data));
+                    innerPid = is.readInt();
+                }
+
+                if (innerPid == -1) {
+                    Log.w(TAG, "Error reading pid from wrapped process, child may have died");
+                }
+            } catch (Exception ex) {
+                Log.w(TAG, "Error reading pid from wrapped process, child may have died", ex);
             }
 
             // Ensure that the pid reported by the wrapped process is either the