c# - SoundPlayer.Play的实现是什么，它不允许播放多个声音异步声音？

Question

我正在尝试了解SoundPlayer.Play的实现中不允许播放多于1个声音异步声音的含义(例如，如here或here所述)。我调查了它的source code，但我不知道。

为了方便起见，这是SoundPlayer.Play和SoundPlayer.LoadAndPlay的代码，这是SoundPlayer.Play调用的方法:

public void Play() {
            LoadAndPlay(NativeMethods.SND_ASYNC);
        }    

private void LoadAndPlay(int flags) {
            // 
            if (String.IsNullOrEmpty(soundLocation) && stream == null) {
                SystemSounds.Beep.Play();
                return;
            }

            if (uri != null && uri.IsFile) {
                // VSW 580992: With more than one thread, someone could call SoundPlayer::set_Location
                // between the time LoadAndPlay demands FileIO and the time it calls PlaySound under elevation.
                // 
                // Another scenario is someone calling SoundPlayer::set_Location between the time
                // LoadAndPlay validates the sound file and the time it calls PlaySound.
                // The SoundPlayer will end up playing an un-validated sound file.
                // The solution is to store the uri.LocalPath on a local variable
                string localPath = uri.LocalPath;

                // request permission to read the file:
                // pass the full path to the FileIOPermission
                FileIOPermission perm = new FileIOPermission(FileIOPermissionAccess.Read, localPath);
                perm.Demand();

                // play the path
                isLoadCompleted = true;
                System.Media.SoundPlayer.IntSecurity.SafeSubWindows.Demand();

                System.ComponentModel.IntSecurity.UnmanagedCode.Assert();
                // ValidateSoundFile calls into the MMIO API so we need UnmanagedCode permissions to do that.
                // And of course we need UnmanagedCode permissions to all Win32::PlaySound method.
                try {
                    // don't use uri.AbsolutePath because that gives problems when there are whitespaces in file names
                    ValidateSoundFile(localPath);
                    UnsafeNativeMethods.PlaySound(localPath, IntPtr.Zero, NativeMethods.SND_NODEFAULT | flags);
                } finally {
                    System.Security.CodeAccessPermission.RevertAssert();
                }
            } else {
                LoadSync();
                ValidateSoundData(streamData);
                System.Media.SoundPlayer.IntSecurity.SafeSubWindows.Demand();

                System.ComponentModel.IntSecurity.UnmanagedCode.Assert();
                try {
                    UnsafeNativeMethods.PlaySound(streamData, IntPtr.Zero, NativeMethods.SND_MEMORY | NativeMethods.SND_NODEFAULT | flags);
                } finally {
                    System.Security.CodeAccessPermission.RevertAssert();
                }
            }
        }

Answer 1

UnsafeNativeMethods.PlaySound(winmm.dll)仅允许在每个过程的特定时间播放单个声音。