[Solved] More than one AsyncServer at the same time?

me-no-dev / ESPAsyncTCP

Async TCP Library for ESP8266

GNU Lesser General Public License v3.0

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[Solved] More than one AsyncServer at the same time? #164

Closed Miq1 closed 3 years ago

Miq1 commented 3 years ago

I have an application here that needs to serve three separate TCP ports - 23 (Telnet), 80 (HTTP) and 502 (Modbus). I have set up three AsyncServer instances in parallel. While this seemed to work at the beginning, I am experiencing crashes now, if I get a Modbus request while a Telnet output is done.

Is it valid at all to run more than one AsyncServer at the same time?

Miq1 commented 3 years ago

I can narrow it down now to a situation, where the Modbus AsyncServer is trying to send a log line to the Telnet AsyncServer. So from within a onData() Modbus callback I am trying to have the Telnet server do a client.write().

Could this provoke a race condition between the two AsyncServers that is 'solved' by the WDT?

Miq1 commented 3 years ago

The reason was:

one server (Modbus) was calling a callback function
the callback function did a write to another server (Telnet)
since we already ran in SYSTEM context, no yield() etc. could have any effect.
this in combination took too long for the WDT watchdog, so the system was reset.

The solution was to write in the callback function into a buffer and have the Telnet server work on the buffer later, after the callback had returned.