/// <summary>
/// Creates a pipe in which the specified ends are inheritable by child processes.
/// In order for the pipe to be closable by the child, the inherited end should be closed after process creation.
/// </summary>
/// <remarks>
/// This implementation creates a named pipe instance and immediately connects it. This is effectively the same implementation
/// as <c>CreatePipe</c> (see %SDXROOT%\minkernel\kernelbase\pipe.c), but we compute a random pipe named rather than using the special
/// 'anonymous' naming case of opening \\.\pipe or \Device\NamedPipe\ (without a subsequent path).
/// We choose to not use <c>CreatePipe</c> since it opens both sides for synchronous I/O. Instead, for running build tools we want the
/// BuildXL side opened for overlapped I/O and the build tool side opened for synchronous I/O (if the build tool side acts as a redirected
/// console handle; recall that synchronous read and write attempts will fail on an async handle, which motivates the <c>CreatePipe</c> defaults
/// in the first place). This is significant since many build tool console pipes are forever silent, and with sync handles we'd need N * 3 threads
/// (stdin, stdout, stderr for N concurrent processes) to pessimistically drain them.
/// </remarks>
public static void CreateInheritablePipe(PipeInheritance inheritance, PipeFlags flags, out SafeFileHandle readHandle, out SafeFileHandle writeHandle)
{
string pipeName = @"\\.\pipe\BuildXL-" + Guid.NewGuid().ToString("N");
writeHandle = ProcessUtilities.CreateNamedPipe(
pipeName,
PipeOpenMode.PipeAccessOutbound | (((flags & PipeFlags.WriteSideAsync) != 0) ? PipeOpenMode.FileFlagOverlapped : 0),
PipeMode.PipeTypeByte | PipeMode.PipeRejectRemoteClients,
nMaxInstances: 1,
nOutBufferSize: PipeBufferSize,
nInBufferSize: PipeBufferSize,
nDefaultTimeout: 0,
lpSecurityAttributes: IntPtr.Zero);
if (writeHandle.IsInvalid)
{
throw new NativeWin32Exception(Marshal.GetLastWin32Error(), "CreateNamedPipeW failed");
}
var readSideFlags = FileFlagsAndAttributes.SecurityAnonymous;
if ((flags & PipeFlags.ReadSideAsync) != 0)
{
readSideFlags |= FileFlagsAndAttributes.FileFlagOverlapped;
}
OpenFileResult openReadSideResult = FileUtilities.TryCreateOrOpenFile(
pipeName,
FileDesiredAccess.GenericRead,
FileShare.None,
FileMode.Open,
readSideFlags,
out readHandle);
if (!openReadSideResult.Succeeded)
{
throw openReadSideResult.CreateExceptionForError();
}
if ((inheritance & PipeInheritance.InheritRead) != 0)
{
SetInheritable(readHandle);
}
if ((inheritance & PipeInheritance.InheritWrite) != 0)
{
SetInheritable(writeHandle);
}
}
/// <summary>
/// Creates a pipe in which the specified ends are inheritable by child processes.
/// In order for the pipe to be closable by the child, the inherited end should be closed after process creation.
/// </summary>
/// <remarks>
/// This implementation creates a named pipe instance and immediately connects it. This is effectively the same implementation
/// as <c>CreatePipe</c> (see %SDXROOT%\minkernel\kernelbase\pipe.c), but we compute a random pipe named rather than using the special
/// 'anonymous' naming case of opening \\.\pipe or \Device\NamedPipe\ (without a subsequent path).
/// We choose to not use <c>CreatePipe</c> since it opens both sides for synchronous I/O. Instead, for running build tools we want the
/// BuildXL side opened for overlapped I/O and the build tool side opened for synchronous I/O (if the build tool side acts as a redirected
/// console handle; recall that synchronous read and write attempts will fail on an async handle, which motivates the <c>CreatePipe</c> defaults
/// in the first place). This is significant since many build tool console pipes are forever silent, and with sync handles we'd need N * 3 threads
/// (stdin, stdout, stderr for N concurrent processes) to pessimistically drain them.
/// </remarks>
public static void CreateInheritablePipe(PipeInheritance inheritance, PipeFlags flags, out SafeFileHandle readHandle, out SafeFileHandle writeHandle)
{
string pipeName = @"\\.\pipe\BuildXL-" + Guid.NewGuid().ToString("N");
writeHandle = ProcessUtilities.CreateNamedPipe(
pipeName,
PipeOpenMode.PipeAccessOutbound | (((flags & PipeFlags.WriteSideAsync) != 0) ? PipeOpenMode.FileFlagOverlapped : 0),
PipeMode.PipeTypeByte | PipeMode.PipeRejectRemoteClients,
nMaxInstances: 1,
nOutBufferSize: PipeBufferSize,
nInBufferSize: PipeBufferSize,
nDefaultTimeout: 0,
lpSecurityAttributes: IntPtr.Zero);
if (writeHandle.IsInvalid)
{
throw new NativeWin32Exception(Marshal.GetLastWin32Error(), "CreateNamedPipeW failed");
}
var readSideFlags = FileFlagsAndAttributes.SecurityAnonymous;
if ((flags & PipeFlags.ReadSideAsync) != 0)
{
readSideFlags |= FileFlagsAndAttributes.FileFlagOverlapped;
}
int maxRetry = 3;
while (true)
{
OpenFileResult openReadSideResult = FileUtilities.TryCreateOrOpenFile(
pipeName,
FileDesiredAccess.GenericRead,
FileShare.None,
FileMode.Open,
readSideFlags,
out readHandle);
if (openReadSideResult.Succeeded)
{
break;
}
if (openReadSideResult.NativeErrorCode != NativeIOConstants.ErrorPipeBusy ||
maxRetry == 0)
{
throw openReadSideResult.CreateExceptionForError();
}
bool success = false;
// Wait for at most 5s.
for (int i = 0; i < 10; ++i)
{
success = ProcessUtilities.WaitNamedPipe(pipeName, 500);
if (success)
{
break;
}
}
if (!success)
{
// After waiting for 5s, pipe is still not ready.
throw new NativeWin32Exception(Marshal.GetLastWin32Error(), "WaitNamedPipe");
}
--maxRetry;
}
if ((inheritance & PipeInheritance.InheritRead) != 0)
{
SetInheritable(readHandle);
}
if ((inheritance & PipeInheritance.InheritWrite) != 0)
{
SetInheritable(writeHandle);
}
}