Initial in-process implementation of some Mojo primitives.

mojo/system/waiter.cc

+// Copyright 2013 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 "mojo/system/waiter.h"
+
+#include <limits>
+
+#include "base/logging.h"
+#include "base/time/time.h"
+
+namespace mojo {
+namespace system {
+
+Waiter::Waiter()
+    : cv_(&lock_),
+      awoken_(false),
+      wait_result_(MOJO_RESULT_INTERNAL) {
+}
+
+Waiter::~Waiter() {
+}
+
+void Waiter::Init() {
+  awoken_ = false;
+  // NOTE(vtl): If performance ever becomes an issue, we can disable the setting
+  // of |wait_result_| (except the first one in |Awake()|) in Release builds.
+  wait_result_ = MOJO_RESULT_INTERNAL;
+}
+
+// TODO(vtl): Fast-path the |deadline == 0| case?
+MojoResult Waiter::Wait(MojoDeadline deadline) {
+  base::AutoLock locker(lock_);
+
+  // Fast-path the already-awoken case:
+  if (awoken_) {
+    DCHECK_NE(wait_result_, MOJO_RESULT_INTERNAL);
+    return wait_result_;
+  }
+
+  // |MojoDeadline| is actually a |uint64_t|, but we need a signed quantity.
+  // Treat any out-of-range deadline as "forever" (which is wrong, but okay
+  // since 2^63 microseconds is ~300000 years). Note that this also takes care
+  // of the |MOJO_DEADLINE_INDEFINITE| (= 2^64 - 1) case.
+  if (deadline > static_cast<uint64_t>(std::numeric_limits<int64_t>::max())) {
+    do {
+      cv_.Wait();
+    } while (!awoken_);
+  } else {
+    // NOTE(vtl): This is very inefficient on POSIX, since pthreads condition
+    // variables take an absolute deadline.
+    const base::TimeTicks end_time = base::TimeTicks::HighResNow() +
+        base::TimeDelta::FromMicroseconds(static_cast<int64_t>(deadline));
+    do {
+      base::TimeTicks now_time = base::TimeTicks::HighResNow();
+      if (now_time >= end_time)
+        return MOJO_RESULT_DEADLINE_EXCEEDED;
+
+      cv_.TimedWait(end_time - now_time);
+    } while (!awoken_);
+  }
+
+  DCHECK_NE(wait_result_, MOJO_RESULT_INTERNAL);
+  return wait_result_;
+}
+
+void Waiter::Awake(MojoResult wait_result) {
+  base::AutoLock locker(lock_);
+
+  if (awoken_)
+    return;
+
+  awoken_ = true;
+  wait_result_ = wait_result;
+  cv_.Signal();
+  // |cv_.Wait()|/|cv_.TimedWait()| will return after |lock_| is released.
+}
+
+}  // namespace system
+}  // namespace mojo