adb: retry connecting disconnected emulators instead of always looping.

Previously we loop through local ports every second, this patch improves
the strategy by retrying only just disconnected emulators.

Bug: 26468076
Bug: 19974213
Bug: 22920867

Change-Id: I43ccb746922d104202b0f81a3d163d850bbc890e
diff --git a/adb/sysdeps/condition_variable.h b/adb/sysdeps/condition_variable.h
new file mode 100644
index 0000000..117cd40
--- /dev/null
+++ b/adb/sysdeps/condition_variable.h
@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2016 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.
+ */
+
+#pragma once
+
+#include <condition_variable>
+
+#include "sysdeps/mutex.h"
+
+#if defined(_WIN32)
+
+#include <windows.h>
+
+#include <android-base/macros.h>
+
+// The prebuilt version of mingw we use doesn't support condition_variable.
+// Therefore, implement our own using the Windows primitives.
+// Put them directly into the std namespace, so that when they're actually available, the build
+// breaks until they're removed.
+
+namespace std {
+
+class condition_variable {
+  public:
+    condition_variable() {
+        InitializeConditionVariable(&cond_);
+    }
+
+    void wait(std::unique_lock<std::mutex>& lock) {
+        std::mutex *m = lock.mutex();
+        m->lock_count_--;
+        SleepConditionVariableCS(&cond_, m->native_handle(), INFINITE);
+        m->lock_count_++;
+    }
+
+    void notify_one() {
+        WakeConditionVariable(&cond_);
+    }
+
+  private:
+    CONDITION_VARIABLE cond_;
+
+    DISALLOW_COPY_AND_ASSIGN(condition_variable);
+};
+
+}
+
+#endif  // defined(_WIN32)
diff --git a/adb/sysdeps/mutex.h b/adb/sysdeps/mutex.h
index 73c9e6e..226f7f1 100644
--- a/adb/sysdeps/mutex.h
+++ b/adb/sysdeps/mutex.h
@@ -1,5 +1,3 @@
-#pragma once
-
 /*
  * Copyright (C) 2016 The Android Open Source Project
  *
@@ -16,6 +14,7 @@
  * limitations under the License.
  */
 
+#pragma once
 #if defined(_WIN32)
 
 #include <windows.h>
@@ -35,34 +34,42 @@
 // CRITICAL_SECTION is recursive, so just wrap it in a Mutex-compatible class.
 class recursive_mutex {
   public:
+    typedef CRITICAL_SECTION* native_handle_type;
+
     recursive_mutex() {
-        InitializeCriticalSection(&mutex_);
+        InitializeCriticalSection(&cs_);
     }
 
     ~recursive_mutex() {
-        DeleteCriticalSection(&mutex_);
+        DeleteCriticalSection(&cs_);
     }
 
     void lock() {
-        EnterCriticalSection(&mutex_);
+        EnterCriticalSection(&cs_);
     }
 
     bool try_lock() {
-        return TryEnterCriticalSection(&mutex_);
+        return TryEnterCriticalSection(&cs_);
     }
 
     void unlock() {
-        LeaveCriticalSection(&mutex_);
+        LeaveCriticalSection(&cs_);
+    }
+
+    native_handle_type native_handle() {
+        return &cs_;
     }
 
   private:
-    CRITICAL_SECTION mutex_;
+    CRITICAL_SECTION cs_;
 
     DISALLOW_COPY_AND_ASSIGN(recursive_mutex);
 };
 
 class mutex {
   public:
+    typedef CRITICAL_SECTION* native_handle_type;
+
     mutex() {
     }
 
@@ -97,11 +104,17 @@
         return true;
     }
 
+    native_handle_type native_handle() {
+        return mutex_.native_handle();
+    }
+
   private:
     recursive_mutex mutex_;
     size_t lock_count_ = 0;
+
+    friend class condition_variable;
 };
 
 }
 
-#endif
+#endif  // defined(_WIN32)