Any reason why execute() delays?

[Steven Schveighoffer]

On 7/27/20 3:13 PM, bauss wrote:
> On Monday, 27 July 2020 at 17:33:23 UTC, Dukc wrote:
>> I know this is probably abusing D, but I wrote this:
>>
>> ```
>> enum bridgePath = <path to bridge.exe>;
>>
>> int main(string[] args)
>> {  import std.process, std.stdio;
>>    auto result = execute(["wine", bridgePath] ~ args[1 .. $]);
>>    result.output.write;
>>    return result.status;
>> }
>> ```
>>
>> However, for some strange reason this one adds up to around 3 seconds 
>> of delay when invoked, compared to invoking `wine bridge.exe <args>` 
>> directly. If I instead write
>>
>> ```
>> int main(string[] args)
>> {  import std.process;
>>    return spawnProcess(["wine", bridgePath] ~ args[1 .. $]).wait;
>> }
>> ```
>>
>> the delay disappears. Does anybody know why?
> 
> Probably because execute() will also collect output etc. so maybe 
> initializing that adds the delay whereas spawnProcess will just spawn 
> the process and nothing else.

3 seconds of delay seems heavy for processing output from the child 
process. Indeed, the difference between execute and spawnProcess is that 
pipes are set up to read the output/error, and those are stored into a 
string before it returns.

But he is also waiting for the process to finish. So I can't see an 
explanation for an *extra* delay.

But what "3 seconds of delay" means could quite depend on what the 
perception is.

spawnProcess is going to inherit the standard handles, and so there is 
no intermediate collecting of output -- you will see output come out 
immediately to the same place as your parent process (probably the 
terminal) as it happens.

I'll give an example, and maybe this is what is happening:

Let's say you have a process that takes 3 seconds to run, and it is 
frequently outputting data to stdout.

If you run it with spawnProcess, you will see these outputs appear as 
they naturally come in.

If you run it with execute, you will see the outputs ONLY after the 
process has ended (3 seconds later).

Is this possibly what is happening?

-Steve