Another way to create a process with attributes, maybe worse maybe better

Raymond Chen

Adam Rosenfield noted that “those sure are a lot of hoops you have to jump through to solve this unusual problem” of specifying which handles are inherited by a new process.

Well, first of all, what’s so wrong with that? You have to jump through a lot of hoops when you are in an unusual situation. But by definition, most people are not in an unusual situation, so it’s an instance of the Pay for Play principle: The simple case should be easy, and it’s okay for the complicated case to be hard. (It’s usually difficult to make the complicated case easy; that’s why it’s called the complicated case.)

The complexity mostly comes from managing the general-purpose PROC_THREAD_ATTRIBUTE_LIST, which is used for things other than just controlling inherited handles. It’s a generic way of passing up to N additional parameters to Create­Process without having to create 2ᴺ different variations of Create­Process.

The Create­Process­With­Explicit­Handles function was just one of the N special-purpose functions that the PROC_THREAD_ATTRIBUTE_LIST tried to avoid having to create. And the special-purpose function naturally takes the special-purpose case and applies the general solution to it. It’s complicated because you are now doing something complicated.

That said, here’s one attempt to make it less complicated: By putting all the complicated stuff closer to the complicated function:

typedef struct PROCTHREADATTRIBUTE {
 DWORD_PTR Attribute;
 PVOID lpValue;
 SIZE_T cbSize;
} PROCTHREADATTRIBUTE;

BOOL CreateProcessWithAttributes(
  __in_opt     LPCTSTR lpApplicationName,
  __inout_opt  LPTSTR lpCommandLine,
  __in_opt     LPSECURITY_ATTRIBUTES lpProcessAttributes,
  __in_opt     LPSECURITY_ATTRIBUTES lpThreadAttributes,
  __in         BOOL bInheritHandles,
  __in         DWORD dwCreationFlags,
  __in_opt     LPVOID lpEnvironment,
  __in_opt     LPCTSTR lpCurrentDirectory,
  __in         LPSTARTUPINFO lpStartupInfo,
  __out        LPPROCESS_INFORMATION lpProcessInformation,
    // here is the new stuff
    __in       DWORD cAttributes,
    __in_ecount(cAttributes) const PROCTHREADATTRIBUTE rgAttributes[])
{
 BOOL fSuccess;
 BOOL fInitialized = FALSE;
 SIZE_T size = 0;
 LPPROC_THREAD_ATTRIBUTE_LIST lpAttributeList = NULL;
 fSuccess = InitializeProcThreadAttributeList(NULL, cAttributes, 0, &size) ||
            GetLastError() == ERROR_INSUFFICIENT_BUFFER;
 if (fSuccess) {
  lpAttributeList = reinterpret_cast<LPPROC_THREAD_ATTRIBUTE_LIST>
                                (HeapAlloc(GetProcessHeap(), 0, size));
  fSuccess = lpAttributeList != NULL;
 }
 if (fSuccess) {
  fSuccess = InitializeProcThreadAttributeList(lpAttributeList,
                    cAttributes, 0, &size);
 }
 if (fSuccess) {
  fInitialized = TRUE;
  for (DWORD index = 0; index < cAttributes && fSuccess; index++) {
   fSuccess = UpdateProcThreadAttribute(lpAttributeList,
                     0, rgAttributes[index].Attribute,
                     rgAttributes[index].lpValue,
                     rgAttributes[index].cbSize, NULL, NULL);
  }
 }
 if (fSuccess) {
  STARTUPINFOEX info;
  ZeroMemory(&info, sizeof(info));
  info.StartupInfo = *lpStartupInfo;
  info.StartupInfo.cb = sizeof(info);
  info.lpAttributeList = lpAttributeList;
  fSuccess = CreateProcess(lpApplicationName,
                           lpCommandLine,
                           lpProcessAttributes,
                           lpThreadAttributes,
                           bInheritHandles,
                           dwCreationFlags | EXTENDED_STARTUPINFO_PRESENT,
                           lpEnvironment,
                           lpCurrentDirectory,
                           &info.StartupInfo,
                           lpProcessInformation);
 }
 if (fInitialized) DeleteProcThreadAttributeList(lpAttributeList);
 if (lpAttributeList) HeapFree(GetProcessHeap(), 0, lpAttributeList);
 return fSuccess;
}

There, now the complexity is there because you’re a generic complex function, so you have no reason to complain.

A caller of this function might go like this:

  HANDLE handles[2] = { handle1, handle2 };
  const PROCTHREADATTRIBUTE attributes[] = {
   {
    PROC_THREAD_ATTRIBUTE_HANDLE_LIST,
    handles,
    sizeof(handles),
   },
  };

  fSuccess = CreateProcessWithAttributes(
                           lpApplicationName,
                           lpCommandLine,
                           lpProcessAttributes,
                           lpThreadAttributes,
                           bInheritHandles,
                           dwCreationFlags,
                           lpEnvironment,
                           lpCurrentDirectory,
                           lpStartupInfo,
                           lpProcessInformation,
                           ARRAYSIZE(attributes),
                           attributes);

Adam hates the “chained success” style and prefers the “goto” style; on the other hand, other people hate gotos. So to be fair, I will choose a coding style that nobody likes. That way everybody is equally unhappy.

BOOL CreateProcessWithAttributes(
  __in_opt     LPCTSTR lpApplicationName,
  __inout_opt  LPTSTR lpCommandLine,
  __in_opt     LPSECURITY_ATTRIBUTES lpProcessAttributes,
  __in_opt     LPSECURITY_ATTRIBUTES lpThreadAttributes,
  __in         BOOL bInheritHandles,
  __in         DWORD dwCreationFlags,
  __in_opt     LPVOID lpEnvironment,
  __in_opt     LPCTSTR lpCurrentDirectory,
  __in         LPSTARTUPINFO lpStartupInfo,
  __out        LPPROCESS_INFORMATION lpProcessInformation,
    // here is the new stuff
    __in       DWORD cAttributes,
    __in_ecount(cAttributes) const PROCTHREADATTRIBUTE rgAttributes[])
{
 BOOL fSuccess = FALSE;
 SIZE_T size = 0;

 if (InitializeProcThreadAttributeList(NULL, cAttributes, 0, &size) ||
     GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
  LPPROC_THREAD_ATTRIBUTE_LIST lpAttributeList =
         reinterpret_cast<LPPROC_THREAD_ATTRIBUTE_LIST>
                                (HeapAlloc(GetProcessHeap(), 0, size));
  if (lpAttributeList != NULL) {
   if (InitializeProcThreadAttributeList(lpAttributeList,
                     cAttributes, 0, &size)) {
    DWORD index;
    for (index = 0;
         index < cAttributes &&
         UpdateProcThreadAttribute(lpAttributeList,
                       0, rgAttributes[index].Attribute,
                       rgAttributes[index].lpValue,
                       rgAttributes[index].cbSize, NULL, NULL);
         index++) {
    }
    if (index >= cAttributes) {
     STARTUPINFOEX info;
     ZeroMemory(&info, sizeof(info));
     info.StartupInfo = *lpStartupInfo;
     info.StartupInfo.cb = sizeof(info);
     info.lpAttributeList = lpAttributeList;
     fSuccess = CreateProcess(
                           lpApplicationName,
                           lpCommandLine,
                           lpProcessAttributes,
                           lpThreadAttributes,
                           bInheritHandles,
                           dwCreationFlags | EXTENDED_STARTUPINFO_PRESENT,
                           lpEnvironment,
                           lpCurrentDirectory,
                           &info.StartupInfo,
                           lpProcessInformation);
    }
    DeleteProcThreadAttributeList(lpAttributeList);
   }
   HeapFree(GetProcessHeap(), 0, lpAttributeList);
  }
 }
 return fSuccess;
}

Those who are really adventuresome could try a version of Create­Process­With­Attributes that uses varargs or std::initializer_list.

Raymond Chen

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