Move platform_thread to base/threading and put in the base namespace. I left a

stub and "using" declarations in the old location to avoid having to change the
entire project at once.

TEST=it compiles
BUG=none
Review URL: http://codereview.chromium.org/6001010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70342 0039d316-1c4b-4281-b951-d872f2087c98

16 files changed, 896 insertions, 8 deletions

diff --git a/base/threading/platform_thread.h b/base/threading/platform_thread.h
new file mode 100644
index 0000000..0a3c75d7
--- /dev/null
+++ b/base/threading/platform_thread.h
@@ -0,0 +1,99 @@
+// Copyright (c) 2010 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.
+
+// WARNING: You should *NOT* be using this class directly.  PlatformThread is
+// the low-level platform-specific abstraction to the OS's threading interface.
+// You should instead be using a message-loop driven Thread, see thread.h.
+
+#ifndef BASE_THREADING_PLATFORM_THREAD_H_
+#define BASE_THREADING_PLATFORM_THREAD_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include <windows.h>
+#elif defined(OS_POSIX)
+#include <pthread.h>
+#if defined(OS_MACOSX)
+#include <mach/mach.h>
+#else  // OS_POSIX && !OS_MACOSX
+#include <unistd.h>
+#endif
+#endif
+
+namespace base {
+
+// PlatformThreadHandle should not be assumed to be a numeric type, since the
+// standard intends to allow pthread_t to be a structure.  This means you
+// should not initialize it to a value, like 0.  If it's a member variable, the
+// constructor can safely "value initialize" using () in the initializer list.
+#if defined(OS_WIN)
+typedef DWORD PlatformThreadId;
+typedef void* PlatformThreadHandle;  // HANDLE
+const PlatformThreadHandle kNullThreadHandle = NULL;
+#elif defined(OS_POSIX)
+typedef pthread_t PlatformThreadHandle;
+const PlatformThreadHandle kNullThreadHandle = 0;
+#if defined(OS_MACOSX)
+typedef mach_port_t PlatformThreadId;
+#else  // OS_POSIX && !OS_MACOSX
+typedef pid_t PlatformThreadId;
+#endif
+#endif
+
+const PlatformThreadId kInvalidThreadId = 0;
+
+// A namespace for low-level thread functions.
+class PlatformThread {
+ public:
+  // Implement this interface to run code on a background thread.  Your
+  // ThreadMain method will be called on the newly created thread.
+  class Delegate {
+   public:
+    virtual ~Delegate() {}
+    virtual void ThreadMain() = 0;
+  };
+
+  // Gets the current thread id, which may be useful for logging purposes.
+  static PlatformThreadId CurrentId();
+
+  // Yield the current thread so another thread can be scheduled.
+  static void YieldCurrentThread();
+
+  // Sleeps for the specified duration (units are milliseconds).
+  static void Sleep(int duration_ms);
+
+  // Sets the thread name visible to a debugger.  This has no effect otherwise.
+  static void SetName(const char* name);
+
+  // Creates a new thread.  The |stack_size| parameter can be 0 to indicate
+  // that the default stack size should be used.  Upon success,
+  // |*thread_handle| will be assigned a handle to the newly created thread,
+  // and |delegate|'s ThreadMain method will be executed on the newly created
+  // thread.
+  // NOTE: When you are done with the thread handle, you must call Join to
+  // release system resources associated with the thread.  You must ensure that
+  // the Delegate object outlives the thread.
+  static bool Create(size_t stack_size, Delegate* delegate,
+                     PlatformThreadHandle* thread_handle);
+
+  // CreateNonJoinable() does the same thing as Create() except the thread
+  // cannot be Join()'d.  Therefore, it also does not output a
+  // PlatformThreadHandle.
+  static bool CreateNonJoinable(size_t stack_size, Delegate* delegate);
+
+  // Joins with a thread created via the Create function.  This function blocks
+  // the caller until the designated thread exits.  This will invalidate
+  // |thread_handle|.
+  static void Join(PlatformThreadHandle thread_handle);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
+};
+
+}  // namespace base
+
+#endif  // BASE_THREADING_PLATFORM_THREAD_H_
diff --git a/base/threading/platform_thread_mac.mm b/base/threading/platform_thread_mac.mm
new file mode 100644
index 0000000..d77307c5
--- /dev/null
+++ b/base/threading/platform_thread_mac.mm
@@ -0,0 +1,54 @@
+// Copyright (c) 2010 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 "base/threading/platform_thread.h"
+
+#import <Foundation/Foundation.h>
+#include <dlfcn.h>
+
+#include "base/logging.h"
+
+namespace base {
+
+// If Cocoa is to be used on more than one thread, it must know that the
+// application is multithreaded.  Since it's possible to enter Cocoa code
+// from threads created by pthread_thread_create, Cocoa won't necessarily
+// be aware that the application is multithreaded.  Spawning an NSThread is
+// enough to get Cocoa to set up for multithreaded operation, so this is done
+// if necessary before pthread_thread_create spawns any threads.
+//
+// http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/chapter_4_section_4.html
+void InitThreading() {
+  static BOOL multithreaded = [NSThread isMultiThreaded];
+  if (!multithreaded) {
+    // +[NSObject class] is idempotent.
+    [NSThread detachNewThreadSelector:@selector(class)
+                             toTarget:[NSObject class]
+                           withObject:nil];
+    multithreaded = YES;
+
+    DCHECK([NSThread isMultiThreaded]);
+  }
+}
+
+// static
+void PlatformThread::SetName(const char* name) {
+  // pthread_setname_np is only available in 10.6 or later, so test
+  // for it at runtime.
+  int (*dynamic_pthread_setname_np)(const char*);
+  *reinterpret_cast<void**>(&dynamic_pthread_setname_np) =
+      dlsym(RTLD_DEFAULT, "pthread_setname_np");
+  if (!dynamic_pthread_setname_np)
+    return;
+
+  // Mac OS X does not expose the length limit of the name, so
+  // hardcode it.
+  const int kMaxNameLength = 63;
+  std::string shortened_name = std::string(name).substr(0, kMaxNameLength);
+  // pthread_setname() fails (harmlessly) in the sandbox, ignore when it does.
+  // See http://crbug.com/47058
+  dynamic_pthread_setname_np(shortened_name.c_str());
+}
+
+}  // namespace base
diff --git a/base/threading/platform_thread_posix.cc b/base/threading/platform_thread_posix.cc
new file mode 100644
index 0000000..0ef4990
--- /dev/null
+++ b/base/threading/platform_thread_posix.cc
@@ -0,0 +1,225 @@
+// Copyright (c) 2010 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 "base/threading/platform_thread.h"
+
+#include <errno.h>
+#include <sched.h>
+
+#include "base/logging.h"
+#include "base/safe_strerror_posix.h"
+#include "base/scoped_ptr.h"
+#include "base/thread_restrictions.h"
+
+#if defined(OS_MACOSX)
+#include <mach/mach.h>
+#include <sys/resource.h>
+#include <algorithm>
+#endif
+
+#if defined(OS_LINUX)
+#include <dlfcn.h>
+#include <sys/prctl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#endif
+
+#if defined(OS_NACL)
+#include <sys/nacl_syscalls.h>
+#endif
+
+namespace base {
+
+#if defined(OS_MACOSX)
+void InitThreading();
+#endif
+
+namespace {
+
+struct ThreadParams {
+  PlatformThread::Delegate* delegate;
+  bool joinable;
+};
+
+void* ThreadFunc(void* params) {
+  ThreadParams* thread_params = static_cast<ThreadParams*>(params);
+  PlatformThread::Delegate* delegate = thread_params->delegate;
+  if (!thread_params->joinable)
+    base::ThreadRestrictions::SetSingletonAllowed(false);
+  delete thread_params;
+  delegate->ThreadMain();
+  return NULL;
+}
+
+bool CreateThread(size_t stack_size, bool joinable,
+                  PlatformThread::Delegate* delegate,
+                  PlatformThreadHandle* thread_handle) {
+#if defined(OS_MACOSX)
+  base::InitThreading();
+#endif  // OS_MACOSX
+
+  bool success = false;
+  pthread_attr_t attributes;
+  pthread_attr_init(&attributes);
+
+  // Pthreads are joinable by default, so only specify the detached attribute if
+  // the thread should be non-joinable.
+  if (!joinable) {
+    pthread_attr_setdetachstate(&attributes, PTHREAD_CREATE_DETACHED);
+  }
+
+#if defined(OS_MACOSX)
+  // The Mac OS X default for a pthread stack size is 512kB.
+  // Libc-594.1.4/pthreads/pthread.c's pthread_attr_init uses
+  // DEFAULT_STACK_SIZE for this purpose.
+  //
+  // 512kB isn't quite generous enough for some deeply recursive threads that
+  // otherwise request the default stack size by specifying 0. Here, adopt
+  // glibc's behavior as on Linux, which is to use the current stack size
+  // limit (ulimit -s) as the default stack size. See
+  // glibc-2.11.1/nptl/nptl-init.c's __pthread_initialize_minimal_internal. To
+  // avoid setting the limit below the Mac OS X default or the minimum usable
+  // stack size, these values are also considered. If any of these values
+  // can't be determined, or if stack size is unlimited (ulimit -s unlimited),
+  // stack_size is left at 0 to get the system default.
+  //
+  // Mac OS X normally only applies ulimit -s to the main thread stack. On
+  // contemporary OS X and Linux systems alike, this value is generally 8MB
+  // or in that neighborhood.
+  if (stack_size == 0) {
+    size_t default_stack_size;
+    struct rlimit stack_rlimit;
+    if (pthread_attr_getstacksize(&attributes, &default_stack_size) == 0 &&
+        getrlimit(RLIMIT_STACK, &stack_rlimit) == 0 &&
+        stack_rlimit.rlim_cur != RLIM_INFINITY) {
+      stack_size = std::max(std::max(default_stack_size,
+                                     static_cast<size_t>(PTHREAD_STACK_MIN)),
+                            static_cast<size_t>(stack_rlimit.rlim_cur));
+    }
+  }
+#endif  // OS_MACOSX
+
+  if (stack_size > 0)
+    pthread_attr_setstacksize(&attributes, stack_size);
+
+  ThreadParams* params = new ThreadParams;
+  params->delegate = delegate;
+  params->joinable = joinable;
+  success = !pthread_create(thread_handle, &attributes, ThreadFunc, params);
+
+  pthread_attr_destroy(&attributes);
+  if (!success)
+    delete params;
+  return success;
+}
+
+}  // namespace
+
+// static
+PlatformThreadId PlatformThread::CurrentId() {
+  // Pthreads doesn't have the concept of a thread ID, so we have to reach down
+  // into the kernel.
+#if defined(OS_MACOSX)
+  return mach_thread_self();
+#elif defined(OS_LINUX)
+  return syscall(__NR_gettid);
+#elif defined(OS_FREEBSD)
+  // TODO(BSD): find a better thread ID
+  return reinterpret_cast<int64>(pthread_self());
+#elif defined(OS_NACL)
+  return pthread_self();
+#endif
+}
+
+// static
+void PlatformThread::YieldCurrentThread() {
+  sched_yield();
+}
+
+// static
+void PlatformThread::Sleep(int duration_ms) {
+  struct timespec sleep_time, remaining;
+
+  // Contains the portion of duration_ms >= 1 sec.
+  sleep_time.tv_sec = duration_ms / 1000;
+  duration_ms -= sleep_time.tv_sec * 1000;
+
+  // Contains the portion of duration_ms < 1 sec.
+  sleep_time.tv_nsec = duration_ms * 1000 * 1000;  // nanoseconds.
+
+  while (nanosleep(&sleep_time, &remaining) == -1 && errno == EINTR)
+    sleep_time = remaining;
+}
+
+// Linux SetName is currently disabled, as we need to distinguish between
+// helper threads (where it's ok to make this call) and the main thread
+// (where making this call renames our process, causing tools like killall
+// to stop working).
+#if 0 && defined(OS_LINUX)
+// static
+void PlatformThread::SetName(const char* name) {
+  // http://0pointer.de/blog/projects/name-your-threads.html
+
+  // glibc recently added support for pthread_setname_np, but it's not
+  // commonly available yet.  So test for it at runtime.
+  int (*dynamic_pthread_setname_np)(pthread_t, const char*);
+  *reinterpret_cast<void**>(&dynamic_pthread_setname_np) =
+      dlsym(RTLD_DEFAULT, "pthread_setname_np");
+
+  if (dynamic_pthread_setname_np) {
+    // This limit comes from glibc, which gets it from the kernel
+    // (TASK_COMM_LEN).
+    const int kMaxNameLength = 15;
+    std::string shortened_name = std::string(name).substr(0, kMaxNameLength);
+    int err = dynamic_pthread_setname_np(pthread_self(),
+                                         shortened_name.c_str());
+    if (err < 0)
+      LOG(ERROR) << "pthread_setname_np: " << safe_strerror(err);
+  } else {
+    // Implementing this function without glibc is simple enough.  (We
+    // don't do the name length clipping as above because it will be
+    // truncated by the callee (see TASK_COMM_LEN above).)
+    int err = prctl(PR_SET_NAME, name);
+    if (err < 0)
+      PLOG(ERROR) << "prctl(PR_SET_NAME)";
+  }
+}
+#elif defined(OS_MACOSX)
+// Mac is implemented in platform_thread_mac.mm.
+#else
+// static
+void PlatformThread::SetName(const char* name) {
+  // Leave it unimplemented.
+
+  // (This should be relatively simple to implement for the BSDs; I
+  // just don't have one handy to test the code on.)
+}
+#endif  // defined(OS_LINUX)
+
+// static
+bool PlatformThread::Create(size_t stack_size, Delegate* delegate,
+                            PlatformThreadHandle* thread_handle) {
+  return CreateThread(stack_size, true /* joinable thread */,
+                      delegate, thread_handle);
+}
+
+// static
+bool PlatformThread::CreateNonJoinable(size_t stack_size, Delegate* delegate) {
+  PlatformThreadHandle unused;
+
+  bool result = CreateThread(stack_size, false /* non-joinable thread */,
+                             delegate, &unused);
+  return result;
+}
+
+// static
+void PlatformThread::Join(PlatformThreadHandle thread_handle) {
+  // Joining another thread may block the current thread for a long time, since
+  // the thread referred to by |thread_handle| may still be running long-lived /
+  // blocking tasks.
+  base::ThreadRestrictions::AssertIOAllowed();
+  pthread_join(thread_handle, NULL);
+}
+
+}  // namespace base
diff --git a/base/threading/platform_thread_unittest.cc b/base/threading/platform_thread_unittest.cc
new file mode 100644
index 0000000..4b49450
--- /dev/null
+++ b/base/threading/platform_thread_unittest.cc
@@ -0,0 +1,106 @@
+// Copyright (c) 2010 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 "base/threading/platform_thread.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+// Trivial tests that thread runs and doesn't crash on create and join ---------
+
+class TrivialThread : public PlatformThread::Delegate {
+ public:
+  TrivialThread() : did_run_(false) {}
+
+  virtual void ThreadMain() {
+    did_run_ = true;
+  }
+
+  bool did_run() const { return did_run_; }
+
+ private:
+  bool did_run_;
+
+  DISALLOW_COPY_AND_ASSIGN(TrivialThread);
+};
+
+TEST(PlatformThreadTest, Trivial) {
+  TrivialThread thread;
+  PlatformThreadHandle handle = kNullThreadHandle;
+
+  ASSERT_FALSE(thread.did_run());
+  ASSERT_TRUE(PlatformThread::Create(0, &thread, &handle));
+  PlatformThread::Join(handle);
+  ASSERT_TRUE(thread.did_run());
+}
+
+TEST(PlatformThreadTest, TrivialTimesTen) {
+  TrivialThread thread[10];
+  PlatformThreadHandle handle[arraysize(thread)];
+
+  for (size_t n = 0; n < arraysize(thread); n++)
+    ASSERT_FALSE(thread[n].did_run());
+  for (size_t n = 0; n < arraysize(thread); n++)
+    ASSERT_TRUE(PlatformThread::Create(0, &thread[n], &handle[n]));
+  for (size_t n = 0; n < arraysize(thread); n++)
+    PlatformThread::Join(handle[n]);
+  for (size_t n = 0; n < arraysize(thread); n++)
+    ASSERT_TRUE(thread[n].did_run());
+}
+
+// Tests of basic thread functions ---------------------------------------------
+
+class FunctionTestThread : public TrivialThread {
+ public:
+  FunctionTestThread() : thread_id_(0) {}
+
+  virtual void ThreadMain() {
+    thread_id_ = PlatformThread::CurrentId();
+    PlatformThread::YieldCurrentThread();
+    PlatformThread::Sleep(50);
+
+    TrivialThread::ThreadMain();
+  }
+
+  PlatformThreadId thread_id() const { return thread_id_; }
+
+ private:
+  PlatformThreadId thread_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(FunctionTestThread);
+};
+
+TEST(PlatformThreadTest, Function) {
+  PlatformThreadId main_thread_id = PlatformThread::CurrentId();
+
+  FunctionTestThread thread;
+  PlatformThreadHandle handle = kNullThreadHandle;
+
+  ASSERT_FALSE(thread.did_run());
+  ASSERT_TRUE(PlatformThread::Create(0, &thread, &handle));
+  PlatformThread::Join(handle);
+  ASSERT_TRUE(thread.did_run());
+  EXPECT_NE(thread.thread_id(), main_thread_id);
+}
+
+TEST(PlatformThreadTest, FunctionTimesTen) {
+  PlatformThreadId main_thread_id = PlatformThread::CurrentId();
+
+  FunctionTestThread thread[10];
+  PlatformThreadHandle handle[arraysize(thread)];
+
+  for (size_t n = 0; n < arraysize(thread); n++)
+    ASSERT_FALSE(thread[n].did_run());
+  for (size_t n = 0; n < arraysize(thread); n++)
+    ASSERT_TRUE(PlatformThread::Create(0, &thread[n], &handle[n]));
+  for (size_t n = 0; n < arraysize(thread); n++)
+    PlatformThread::Join(handle[n]);
+  for (size_t n = 0; n < arraysize(thread); n++) {
+    ASSERT_TRUE(thread[n].did_run());
+    EXPECT_NE(thread[n].thread_id(), main_thread_id);
+  }
+}
+
+}  // namespace base
diff --git a/base/threading/platform_thread_win.cc b/base/threading/platform_thread_win.cc
new file mode 100644
index 0000000..10f3011
--- /dev/null
+++ b/base/threading/platform_thread_win.cc
@@ -0,0 +1,147 @@
+// Copyright (c) 2010 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 "base/threading/platform_thread.h"
+
+#include "base/logging.h"
+#include "base/thread_restrictions.h"
+#include "base/win/windows_version.h"
+
+namespace base {
+
+namespace {
+
+// The information on how to set the thread name comes from
+// a MSDN article: http://msdn2.microsoft.com/en-us/library/xcb2z8hs.aspx
+const DWORD kVCThreadNameException = 0x406D1388;
+
+typedef struct tagTHREADNAME_INFO {
+  DWORD dwType;  // Must be 0x1000.
+  LPCSTR szName;  // Pointer to name (in user addr space).
+  DWORD dwThreadID;  // Thread ID (-1=caller thread).
+  DWORD dwFlags;  // Reserved for future use, must be zero.
+} THREADNAME_INFO;
+
+struct ThreadParams {
+  PlatformThread::Delegate* delegate;
+  bool joinable;
+};
+
+DWORD __stdcall ThreadFunc(void* params) {
+  ThreadParams* thread_params = static_cast<ThreadParams*>(params);
+  PlatformThread::Delegate* delegate = thread_params->delegate;
+  if (!thread_params->joinable)
+    base::ThreadRestrictions::SetSingletonAllowed(false);
+  delete thread_params;
+  delegate->ThreadMain();
+  return NULL;
+}
+
+// CreateThreadInternal() matches PlatformThread::Create(), except that
+// |out_thread_handle| may be NULL, in which case a non-joinable thread is
+// created.
+bool CreateThreadInternal(size_t stack_size,
+                          PlatformThread::Delegate* delegate,
+                          PlatformThreadHandle* out_thread_handle) {
+  PlatformThreadHandle thread_handle;
+  unsigned int flags = 0;
+  if (stack_size > 0 && base::win::GetVersion() >= base::win::VERSION_XP) {
+    flags = STACK_SIZE_PARAM_IS_A_RESERVATION;
+  } else {
+    stack_size = 0;
+  }
+
+  ThreadParams* params = new ThreadParams;
+  params->delegate = delegate;
+  params->joinable = out_thread_handle != NULL;
+
+  // Using CreateThread here vs _beginthreadex makes thread creation a bit
+  // faster and doesn't require the loader lock to be available.  Our code will
+  // have to work running on CreateThread() threads anyway, since we run code
+  // on the Windows thread pool, etc.  For some background on the difference:
+  //   http://www.microsoft.com/msj/1099/win32/win321099.aspx
+  thread_handle = CreateThread(
+      NULL, stack_size, ThreadFunc, params, flags, NULL);
+  if (!thread_handle) {
+    delete params;
+    return false;
+  }
+
+  if (out_thread_handle)
+    *out_thread_handle = thread_handle;
+  else
+    CloseHandle(thread_handle);
+  return true;
+}
+
+}  // namespace
+
+// static
+PlatformThreadId PlatformThread::CurrentId() {
+  return GetCurrentThreadId();
+}
+
+// static
+void PlatformThread::YieldCurrentThread() {
+  ::Sleep(0);
+}
+
+// static
+void PlatformThread::Sleep(int duration_ms) {
+  ::Sleep(duration_ms);
+}
+
+// static
+void PlatformThread::SetName(const char* name) {
+  // The debugger needs to be around to catch the name in the exception.  If
+  // there isn't a debugger, we are just needlessly throwing an exception.
+  if (!::IsDebuggerPresent())
+    return;
+
+  THREADNAME_INFO info;
+  info.dwType = 0x1000;
+  info.szName = name;
+  info.dwThreadID = CurrentId();
+  info.dwFlags = 0;
+
+  __try {
+    RaiseException(kVCThreadNameException, 0, sizeof(info)/sizeof(DWORD),
+                   reinterpret_cast<DWORD_PTR*>(&info));
+  } __except(EXCEPTION_CONTINUE_EXECUTION) {
+  }
+}
+
+// static
+bool PlatformThread::Create(size_t stack_size, Delegate* delegate,
+                            PlatformThreadHandle* thread_handle) {
+  DCHECK(thread_handle);
+  return CreateThreadInternal(stack_size, delegate, thread_handle);
+}
+
+// static
+bool PlatformThread::CreateNonJoinable(size_t stack_size, Delegate* delegate) {
+  return CreateThreadInternal(stack_size, delegate, NULL);
+}
+
+// static
+void PlatformThread::Join(PlatformThreadHandle thread_handle) {
+  DCHECK(thread_handle);
+  // TODO(willchan): Enable this check once I can get it to work for Windows
+  // shutdown.
+  // Joining another thread may block the current thread for a long time, since
+  // the thread referred to by |thread_handle| may still be running long-lived /
+  // blocking tasks.
+#if 0
+  base::ThreadRestrictions::AssertIOAllowed();
+#endif
+
+  // Wait for the thread to exit.  It should already have terminated but make
+  // sure this assumption is valid.
+  DWORD result = WaitForSingleObject(thread_handle, INFINITE);
+  DCHECK_EQ(WAIT_OBJECT_0, result);
+
+  CloseHandle(thread_handle);
+}
+
+}  // namespace base
diff --git a/base/threading/simple_thread.cc b/base/threading/simple_thread.cc
index df1953f..2b030f6 100644
--- a/base/threading/simple_thread.cc
+++ b/base/threading/simple_thread.cc
@@ -5,7 +5,7 @@
 #include "base/threading/simple_thread.h"
 
 #include "base/logging.h"
-#include "base/platform_thread.h"
+#include "base/threading/platform_thread.h"
 #include "base/string_number_conversions.h"
 
 namespace base {
diff --git a/base/threading/simple_thread.h b/base/threading/simple_thread.h
index dbff3ae..c401e01 100644
--- a/base/threading/simple_thread.h
+++ b/base/threading/simple_thread.h
@@ -47,8 +47,8 @@
 
 #include "base/basictypes.h"
 #include "base/lock.h"
+#include "base/threading/platform_thread.h"
 #include "base/waitable_event.h"
-#include "base/platform_thread.h"
 
 namespace base {
 
diff --git a/base/threading/thread_checker.cc b/base/threading/thread_checker.cc
new file mode 100644
index 0000000..28ba400
--- /dev/null
+++ b/base/threading/thread_checker.cc
@@ -0,0 +1,38 @@
+// Copyright (c) 2010 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 "base/threading/thread_checker.h"
+
+// This code is only done in debug builds.
+#ifndef NDEBUG
+
+namespace base {
+
+ThreadChecker::ThreadChecker() : valid_thread_id_(kInvalidThreadId) {
+  EnsureThreadIdAssigned();
+}
+
+ThreadChecker::~ThreadChecker() {}
+
+bool ThreadChecker::CalledOnValidThread() const {
+  EnsureThreadIdAssigned();
+  AutoLock auto_lock(lock_);
+  return valid_thread_id_ == PlatformThread::CurrentId();
+}
+
+void ThreadChecker::DetachFromThread() {
+  AutoLock auto_lock(lock_);
+  valid_thread_id_ = kInvalidThreadId;
+}
+
+void ThreadChecker::EnsureThreadIdAssigned() const {
+  AutoLock auto_lock(lock_);
+  if (valid_thread_id_ != kInvalidThreadId)
+    return;
+  valid_thread_id_ = PlatformThread::CurrentId();
+}
+
+}  // namespace base
+
+#endif  // NDEBUG
diff --git a/base/threading/thread_checker.h b/base/threading/thread_checker.h
new file mode 100644
index 0000000..c0010fb
--- /dev/null
+++ b/base/threading/thread_checker.h
@@ -0,0 +1,73 @@
+// Copyright (c) 2010 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.
+
+#ifndef BASE_THREADING_THREAD_CHECKER_H_
+#define BASE_THREADING_THREAD_CHECKER_H_
+#pragma once
+
+#ifndef NDEBUG
+#include "base/lock.h"
+#include "base/threading/platform_thread.h"
+#endif // NDEBUG
+
+namespace base {
+
+// Before using this class, please consider using NonThreadSafe as it
+// makes it much easier to determine the nature of your class.
+//
+// A helper class used to help verify that some methods of a class are
+// called from the same thread.  One can inherit from this class and use
+// CalledOnValidThread() to verify.
+//
+// Inheriting from class indicates that one must be careful when using the class
+// with multiple threads. However, it is up to the class document to indicate
+// how it can be used with threads.
+//
+// Example:
+// class MyClass : public ThreadChecker {
+//  public:
+//   void Foo() {
+//     DCHECK(CalledOnValidThread());
+//     ... (do stuff) ...
+//   }
+// }
+//
+// In Release mode, CalledOnValidThread will always return true.
+//
+#ifndef NDEBUG
+class ThreadChecker {
+ public:
+  ThreadChecker();
+  ~ThreadChecker();
+
+  bool CalledOnValidThread() const;
+
+  // Changes the thread that is checked for in CalledOnValidThread.  This may
+  // be useful when an object may be created on one thread and then used
+  // exclusively on another thread.
+  void DetachFromThread();
+
+ private:
+  void EnsureThreadIdAssigned() const;
+
+  mutable Lock lock_;
+  // This is mutable so that CalledOnValidThread can set it.
+  // It's guarded by |lock_|.
+  mutable PlatformThreadId valid_thread_id_;
+};
+#else
+// Do nothing in release mode.
+class ThreadChecker {
+ public:
+  bool CalledOnValidThread() const {
+    return true;
+  }
+
+  void DetachFromThread() {}
+};
+#endif  // NDEBUG
+
+}  // namespace base
+
+#endif  // BASE_THREADING_THREAD_CHECKER_H_
diff --git a/base/threading/thread_checker_unittest.cc b/base/threading/thread_checker_unittest.cc
new file mode 100644
index 0000000..6ce5bf1
--- /dev/null
+++ b/base/threading/thread_checker_unittest.cc
@@ -0,0 +1,146 @@
+// Copyright (c) 2010 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 "base/basictypes.h"
+#include "base/logging.h"
+#include "base/scoped_ptr.h"
+#include "base/threading/thread_checker.h"
+#include "base/threading/simple_thread.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+#ifndef NDEBUG
+
+namespace base {
+
+// Simple class to exersice the basics of ThreadChecker.
+// Both the destructor and DoStuff should verify that they were
+// called on the same thread as the constructor.
+class ThreadCheckerClass : public ThreadChecker {
+ public:
+  ThreadCheckerClass() {}
+
+  // Verifies that it was called on the same thread as the constructor.
+  void DoStuff() {
+    DCHECK(CalledOnValidThread());
+  }
+
+  void DetachFromThread() {
+    ThreadChecker::DetachFromThread();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ThreadCheckerClass);
+};
+
+// Calls ThreadCheckerClass::DoStuff on another thread.
+class CallDoStuffOnThread : public base::SimpleThread {
+ public:
+  CallDoStuffOnThread(ThreadCheckerClass* thread_checker_class)
+      : SimpleThread("call_do_stuff_on_thread"),
+        thread_checker_class_(thread_checker_class) {
+  }
+
+  virtual void Run() {
+    thread_checker_class_->DoStuff();
+  }
+
+ private:
+  ThreadCheckerClass* thread_checker_class_;
+
+  DISALLOW_COPY_AND_ASSIGN(CallDoStuffOnThread);
+};
+
+// Deletes ThreadCheckerClass on a different thread.
+class DeleteThreadCheckerClassOnThread : public base::SimpleThread {
+ public:
+  DeleteThreadCheckerClassOnThread(ThreadCheckerClass* thread_checker_class)
+      : SimpleThread("delete_thread_checker_class_on_thread"),
+        thread_checker_class_(thread_checker_class) {
+  }
+
+  virtual void Run() {
+    thread_checker_class_.reset();
+  }
+
+ private:
+  scoped_ptr<ThreadCheckerClass> thread_checker_class_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeleteThreadCheckerClassOnThread);
+};
+
+TEST(ThreadCheckerTest, CallsAllowedOnSameThread) {
+  scoped_ptr<ThreadCheckerClass> thread_checker_class(
+      new ThreadCheckerClass);
+
+  // Verify that DoStuff doesn't assert.
+  thread_checker_class->DoStuff();
+
+  // Verify that the destructor doesn't assert.
+  thread_checker_class.reset();
+}
+
+TEST(ThreadCheckerTest, DestructorAllowedOnDifferentThread) {
+  scoped_ptr<ThreadCheckerClass> thread_checker_class(
+      new ThreadCheckerClass);
+
+  // Verify that the destructor doesn't assert
+  // when called on a different thread.
+  DeleteThreadCheckerClassOnThread delete_on_thread(
+      thread_checker_class.release());
+
+  delete_on_thread.Start();
+  delete_on_thread.Join();
+}
+
+TEST(ThreadCheckerTest, DetachFromThread) {
+  scoped_ptr<ThreadCheckerClass> thread_checker_class(
+      new ThreadCheckerClass);
+
+  // Verify that DoStuff doesn't assert when called on a different thread after
+  // a call to DetachFromThread.
+  thread_checker_class->DetachFromThread();
+  CallDoStuffOnThread call_on_thread(thread_checker_class.get());
+
+  call_on_thread.Start();
+  call_on_thread.Join();
+}
+
+#if GTEST_HAS_DEATH_TEST
+
+TEST(ThreadCheckerDeathTest, MethodNotAllowedOnDifferentThread) {
+  ASSERT_DEBUG_DEATH({
+      scoped_ptr<ThreadCheckerClass> thread_checker_class(
+          new ThreadCheckerClass);
+
+      // Verify that DoStuff asserts when called on a different thread.
+      CallDoStuffOnThread call_on_thread(thread_checker_class.get());
+
+      call_on_thread.Start();
+      call_on_thread.Join();
+    }, "");
+}
+
+TEST(ThreadCheckerDeathTest, DetachFromThread) {
+  ASSERT_DEBUG_DEATH({
+      scoped_ptr<ThreadCheckerClass> thread_checker_class(
+          new ThreadCheckerClass);
+
+      // Verify that DoStuff doesn't assert when called on a different thread
+      // after a call to DetachFromThread.
+      thread_checker_class->DetachFromThread();
+      CallDoStuffOnThread call_on_thread(thread_checker_class.get());
+
+      call_on_thread.Start();
+      call_on_thread.Join();
+
+      // Verify that DoStuff asserts after moving to another thread.
+      thread_checker_class->DoStuff();
+    }, "");
+}
+
+#endif  // GTEST_HAS_DEATH_TEST
+
+}  // namespace base
+
+#endif  // NDEBUG
diff --git a/base/threading/watchdog.cc b/base/threading/watchdog.cc
index 8474744..cd21578 100644
--- a/base/threading/watchdog.cc
+++ b/base/threading/watchdog.cc
@@ -6,7 +6,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
-#include "base/platform_thread.h"
+#include "base/threading/platform_thread.h"
 
 namespace base {
 
diff --git a/base/threading/watchdog.h b/base/threading/watchdog.h
index 025fe09..8641f04 100644
--- a/base/threading/watchdog.h
+++ b/base/threading/watchdog.h
@@ -23,7 +23,7 @@
 
 #include "base/condition_variable.h"
 #include "base/lock.h"
-#include "base/platform_thread.h"
+#include "base/threading/platform_thread.h"
 #include "base/time.h"
 
 namespace base {
diff --git a/base/threading/watchdog_unittest.cc b/base/threading/watchdog_unittest.cc
index 347781e..f96487b 100644
--- a/base/threading/watchdog_unittest.cc
+++ b/base/threading/watchdog_unittest.cc
@@ -5,8 +5,8 @@
 #include "base/threading/watchdog.h"
 
 #include "base/logging.h"
-#include "base/platform_thread.h"
 #include "base/spin_wait.h"
+#include "base/threading/platform_thread.h"
 #include "base/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
diff --git a/base/threading/worker_pool_posix.cc b/base/threading/worker_pool_posix.cc
index 2facc01..8466403 100644
--- a/base/threading/worker_pool_posix.cc
+++ b/base/threading/worker_pool_posix.cc
@@ -6,10 +6,10 @@
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
-#include "base/platform_thread.h"
 #include "base/ref_counted.h"
 #include "base/stringprintf.h"
 #include "base/task.h"
+#include "base/threading/platform_thread.h"
 #include "base/threading/worker_pool.h"
 
 namespace base {
diff --git a/base/threading/worker_pool_posix.h b/base/threading/worker_pool_posix.h
index 6c99e76..44f0208 100644
--- a/base/threading/worker_pool_posix.h
+++ b/base/threading/worker_pool_posix.h
@@ -31,9 +31,9 @@
 #include "base/basictypes.h"
 #include "base/condition_variable.h"
 #include "base/lock.h"
-#include "base/platform_thread.h"
 #include "base/ref_counted.h"
 #include "base/scoped_ptr.h"
+#include "base/threading/platform_thread.h"
 
 class Task;
 
diff --git a/base/threading/worker_pool_posix_unittest.cc b/base/threading/worker_pool_posix_unittest.cc
index 48df16e..25509bf 100644
--- a/base/threading/worker_pool_posix_unittest.cc
+++ b/base/threading/worker_pool_posix_unittest.cc
@@ -8,8 +8,8 @@
 
 #include "base/condition_variable.h"
 #include "base/lock.h"
-#include "base/platform_thread.h"
 #include "base/task.h"
+#include "base/threading/platform_thread.h"
 #include "base/waitable_event.h"
 #include "testing/gtest/include/gtest/gtest.h"