Update sandbox/linux from upstream

sandbox/linux/services/thread_helpers.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sandbox/linux/services/thread_helpers.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <sys/types.h>
@@ skipping 11 matching lines @@
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread.h"
 #include "sandbox/linux/services/proc_util.h"
 
 namespace sandbox {
 
 namespace {
 
 const char kAssertSingleThreadedError[] =
     "Current process is not mono-threaded!";
+const char kAssertThreadDoesNotAppearInProcFS[] =
+    "Started thread does not appear in /proc";
+const char kAssertThreadDoesNotDisappearInProcFS[] =
+    "Stopped thread does not disappear in /proc";
 
 bool IsSingleThreadedImpl(int proc_fd) {
   CHECK_LE(0, proc_fd);
   struct stat task_stat;
   int fstat_ret = fstatat(proc_fd, "self/task/", &task_stat, 0);
   PCHECK(0 == fstat_ret);
 
   // At least "..", "." and the current thread should be present.
   CHECK_LE(3UL, task_stat.st_nlink);
   // Counting threads via /proc/self/task could be racy. For the purpose of
   // determining if the current proces is monothreaded it works: if at any
   // time it becomes monothreaded, it'll stay so.
   return task_stat.st_nlink == 3;
 }
 
 bool IsThreadPresentInProcFS(int proc_fd,
                              const std::string& thread_id_dir_str) {
   struct stat task_stat;
   const int fstat_ret =
       fstatat(proc_fd, thread_id_dir_str.c_str(), &task_stat, 0);
   if (fstat_ret < 0) {
     PCHECK(ENOENT == errno);
     return false;
   }
   return true;
 }
 
+bool IsNotThreadPresentInProcFS(int proc_fd,
+                                const std::string& thread_id_dir_str) {
+  return !IsThreadPresentInProcFS(proc_fd, thread_id_dir_str);
+}
+
 // Run |cb| in a loop until it returns false. Every time |cb| runs, sleep
 // for an exponentially increasing amount of time. |cb| is expected to return
 // false very quickly and this will crash if it doesn't happen within ~64ms on
 // Debug builds (2s on Release builds).
 // This is guaranteed to not sleep more than twice as much as the bare minimum
 // amount of time.
-void RunWhileTrue(const base::Callback<bool(void)>& cb) {
+void RunWhileTrue(const base::Callback<bool(void)>& cb, const char* message) {
 #if defined(NDEBUG)
   // In Release mode, crash after 30 iterations, which means having spent
   // roughly 2s in
   // nanosleep(2) cumulatively.
   const unsigned int kMaxIterations = 30U;
 #else
   // In practice, this never goes through more than a couple iterations. In
   // debug mode, crash after 64ms (+ eventually 25 times the granularity of
   // the clock) in nanosleep(2). This ensures that this is not becoming too
   // slow.
   const unsigned int kMaxIterations = 25U;
 #endif
 
   // Run |cb| with an exponential back-off, sleeping 2^iterations nanoseconds
   // in nanosleep(2).
   // Note: the clock may not allow for nanosecond granularity, in this case the
   // first iterations would sleep a tiny bit more instead, which would not
   // change the calculations significantly.
   for (unsigned int i = 0; i < kMaxIterations; ++i) {
     if (!cb.Run()) {
       return;
     }
 
     // Increase the waiting time exponentially.
     struct timespec ts = {0, 1L << i /* nanoseconds */};
     PCHECK(0 == HANDLE_EINTR(nanosleep(&ts, &ts)));
   }
 
-  LOG(FATAL) << kAssertSingleThreadedError << " (iterations: " << kMaxIterations
-             << ")";
+  LOG(FATAL) << message << " (iterations: " << kMaxIterations << ")";
 
   NOTREACHED();
 }
 
 bool IsMultiThreaded(int proc_fd) {
   return !ThreadHelpers::IsSingleThreaded(proc_fd);
 }
 
+enum class ThreadAction { Start, Stop };
+
+bool ChangeThreadStateAndWatchProcFS(
+    int proc_fd, base::Thread* thread, ThreadAction action) {
+  DCHECK_LE(0, proc_fd);
+  DCHECK(thread);
+  DCHECK(action == ThreadAction::Start || action == ThreadAction::Stop);
+
+  base::Callback<bool(void)> cb;
+  const char* message;
+
+  if (action == ThreadAction::Start) {
+    // Should start the thread before calling thread_id().
+    if (!thread->Start())
+      return false;
+  }
+
+  const base::PlatformThreadId thread_id = thread->thread_id();
+  const std::string thread_id_dir_str =
+      "self/task/" + base::IntToString(thread_id) + "/";
+
+  if (action == ThreadAction::Stop) {
+    // The target thread should exist in /proc.
+    DCHECK(IsThreadPresentInProcFS(proc_fd, thread_id_dir_str));
+    thread->Stop();
+  }
+
+  // The kernel is at liberty to wake the thread id futex before updating
+  // /proc. Start() above or following Stop(), the thread is started or joined,
+  // but entries in /proc may not have been updated.
+  if (action == ThreadAction::Start) {
+    cb = base::Bind(&IsNotThreadPresentInProcFS, proc_fd, thread_id_dir_str);
+    message = kAssertThreadDoesNotAppearInProcFS;
+  } else {
+    cb = base::Bind(&IsThreadPresentInProcFS, proc_fd, thread_id_dir_str);
+    message = kAssertThreadDoesNotDisappearInProcFS;
+  }
+  RunWhileTrue(cb, message);
+
+  DCHECK_EQ(action == ThreadAction::Start,
+            IsThreadPresentInProcFS(proc_fd, thread_id_dir_str));
+
+  return true;
+}
+
 }  // namespace
 
 // static
 bool ThreadHelpers::IsSingleThreaded(int proc_fd) {
   DCHECK_LE(0, proc_fd);
   return IsSingleThreadedImpl(proc_fd);
 }
 
 // static
 bool ThreadHelpers::IsSingleThreaded() {
   base::ScopedFD task_fd(ProcUtil::OpenProc());
   return IsSingleThreaded(task_fd.get());
 }
 
 // static
 void ThreadHelpers::AssertSingleThreaded(int proc_fd) {
   DCHECK_LE(0, proc_fd);
   const base::Callback<bool(void)> cb = base::Bind(&IsMultiThreaded, proc_fd);
-  RunWhileTrue(cb);
+  RunWhileTrue(cb, kAssertSingleThreadedError);
 }
 
 void ThreadHelpers::AssertSingleThreaded() {
   base::ScopedFD task_fd(ProcUtil::OpenProc());
   AssertSingleThreaded(task_fd.get());
 }
 
 // static
+bool ThreadHelpers::StartThreadAndWatchProcFS(int proc_fd,
+                                              base::Thread* thread) {
+  return ChangeThreadStateAndWatchProcFS(proc_fd, thread, ThreadAction::Start);
+}
+
+// static
 bool ThreadHelpers::StopThreadAndWatchProcFS(int proc_fd,
                                              base::Thread* thread) {
-  DCHECK_LE(0, proc_fd);
-  DCHECK(thread);
-  const base::PlatformThreadId thread_id = thread->thread_id();
-  const std::string thread_id_dir_str =
-      "self/task/" + base::IntToString(thread_id) + "/";
-
-  // The kernel is at liberty to wake the thread id futex before updating
-  // /proc. Following Stop(), the thread is joined, but entries in /proc may
-  // not have been updated.
-  thread->Stop();
-
-  const base::Callback<bool(void)> cb =
-      base::Bind(&IsThreadPresentInProcFS, proc_fd, thread_id_dir_str);
-
-  RunWhileTrue(cb);
-
-  return true;
+  return ChangeThreadStateAndWatchProcFS(proc_fd, thread, ThreadAction::Stop);
 }
 
 // static
 const char* ThreadHelpers::GetAssertSingleThreadedErrorMessageForTests() {
   return kAssertSingleThreadedError;
 }
 
 }  // namespace sandbox