[R-pkg-devel] socketConnection, delay when reading from

[Ben Engbers]

Op 08-12-2021 om 12:40 schreef Tomas Kalibera:
> On 12/8/21 12:20 PM, Ben Engbers wrote:
>> Op 07-12-2021 om 23:49 schreef Ben Engbers:


>> The new code, which now uses a non-blocking socket, takes less than 4 
>> seconds to execute the 53 tests. Compared to the 120 seconds when 
>> using a blocking socket, this was worth the effort.
> 
> Ok, this confirms there is a race condition, but the next step should be 
> removing it, so that it works reliably. Actually, one way to test that 
> such programs are race-free is to actually on purpose insert sleeps at 
> various locations - the programs then should still work.
> 
> I am not able to give more specific advice based on the code snippet you 
> sent yesterday, but in principle, you can use socketSelect() to wait for 
> the connection to become ready to be read from. In either case, there 
> needs to be some way to tell whether the received data is complete. 
> Either you know the length, or there is some special mark in the data, 
> there has to be something.

writeBin(auth, private$conn)
Sys.sleep(.1)
Accepted <- readBin(conn, what = "raw", n = 1) == 0

I checked in the debugger that auth has the correct length. And 
readBin(conn, what = "raw", n = 1) should return exactly 1 byte (either 
0x00 or 0x01.

You say that socketSelect() can be used to wait for the connection to 
become ready.
How? The only option I see is a "no-delay". Should I set this to FALSE? 
I tried adding 'options = getOption(c("no-delay = <value>"))' when 
creating the socketConnection. In the tesfile (see below) value TRUE or 
FALSE were both accepted. In the package, createSocket still failed.

> If you need more help from people on the list, it might be better to 
> send a small, but full complete example, so also with a server, so that 
> it is something people could run and reproduce.

The server can be downloaded from https://basex.org/download/. After 
unzipping it can be started with 'basexserver &'.

I have attached a testfile.

Ben
> 
> Best
> Tomas