Is there a function better than API SLEEP?

[leesing2k3]

I have read that from the internet that API sleep minimum delay is 10ms even though it is "sleep 1".

Is there a function that is almost like the API sleep but much more precise? Real 1millisecond delay?

I have seen some multimedia timer that is able to set the interval to 1ms and it really does. But I really need SLEEP function to do the job.

Thank you.

[Dmorley]

SleepEx??

Declare Function SleepEx Lib "kernel32.dll" (ByVal dwMilliseconds As Long, ByVal bAlertable As Long) As Long

[leesing2k3]

SleepEx isnt the one that I am looking for.

[wildfrog]

I have read that from the internet that API sleep minimum delay is 10ms even though it is "sleep 1".

A simple test shows me that Sleep(1) on my computer takes approx 1.9ms, but as far as I know thats really up to the hardware. Anyway, in a multithreading environment, calling Sleep(...) suspends the thread for atleast X milliiseconds, and yields the processor to other waiting threads/processes.

Is there a function that is almost like the API sleep but much more precise? Real 1millisecond delay?

There is a function in kernel32.dll, called ZwDelayExecution(...) which let you specify the delay in units of 100ns.
- petter

[WizBang]

It might be worth pointing out that vb isn't fast enough for one millisecond accuracy. That may be tricky for any language in fact, though I've not looked into it. Many times what seems like a need for this accuracy is really a need to measure the passage of time with precision, not control it. It would probably be worthwhile for you to give some details on what you are trying to accomplish. There are always different approaches, and someone is bound to know of at least one or two that can work for you.

[leesing2k3]

Omg, finding information about ZwDelayExecution is very hard.

Not much information can be found in google or yahoo.

[wildfrog]

It's not in kernel32, it's in ntdll, sorry for that.

The signature of the function is:

NTSYSAPI NTSTATUS NTAPI ZwDelayExecution(IN BOOLEAN Alertable, IN PLARGE_INTEGER Interval)

- or more readable -

DWORD __stdcall ZwDelayExecution(BOOLEAN Alertable, __int64* Interval)

The Alertable specified whether to "sleep" in an alertable state or not.
The Interval, a pointer to a 64 bit integer, is somewhat 2 sided. If it is negative it specifies the relative time to sleep (in units of 100ns), if not is specifies the absolute time to wake up.

With my limited knowlege I'm not sure if it's possible to call this function from VB at all.

But here's some non error-checking C code:

#include <windows.h> 
 
typedef  DWORD (__stdcall *pfZwDelayExecution)(BOOLEAN, __int64*); 
 
int _tmain(int argc, _TCHAR* argv[])
{
    HINSTANCE hinstLib; 
    pfZwDelayExecution ZwDelayExecution; 
 
    // Get a handle to the DLL module.
    hinstLib = LoadLibrary(TEXT("ntdll")); 
 
    // Get the pointer to the function
    ZwDelayExecution = (pfZwDelayExecution) GetProcAddress(hinstLib, "ZwDelayExecution"); 

    // sleep for 20 milliseconds
    __int64 x = -200000;
    ZwDelayExecution(FALSE, &x);
 
    // Free the DLL module.
     fFreeResult = FreeLibrary(hinstLib); 
}

- petter

[leesing2k3]

Public Declare Sub DelayExecution Lib "ntdll.dll" Alias "ZwDelayExecution" (ByVal Alertable As Boolean, ByVal Interval As Long)

I do this and I call this

DelayExecution False, 300000000
and
DelayExecution False, -300000000

and it doesnt seem to delay

[wildfrog]

Again, with no understanding of VB, the second argument, Interval is a pointer to an 64 bit integer (AFAIK long is a 32 bit integer).

If you got a 64 bit integer type (LONG LONG) in VB you could try something like this:

Public Declare Sub DelayExecution Lib "ntdll.dll" Alias "ZwDelayExecution" (ByVal Alertable As Boolean, ByRef Interval As Long Long)

Dim Interval as Long Long
Interval = -300000000
DelayExecution False, ByRef Interval

- petter

[leesing2k3]

According to wildfrog

The signature of the function is:
NTSYSAPI NTSTATUS NTAPI ZwDelayExecution(IN BOOLEAN Alertable, IN PLARGE_INTEGER Interval)
- or more readable -
DWORD __stdcall ZwDelayExecution(BOOLEAN Alertable, __int64* Interval)

This call is almost like the API Sleep but with a delay in units of 100ns.

[WizBang]

The Currency data type is 64 bits, but supports a decimal point. Still, the question is, why the need for such precision delay times? As stated, vb is just not fast enough even with such an API. You could end up banging you head against a wall on this one. If you can elaborate on what you're doing, we might have some simple alternative suggestions.