Crash when expedition port is destroyed while wares are unloaded

[wl-zocker]

This issue was found by dax831 in our forum [1] in build 18, but it still happens in r7237 (both on Win7).

To reproduce either use the savegame from the forum (build 18), it crashes after some seconds. The reason is that the port space north-west to the starting viewpoint is conquered by the red player and the construction site is destroyed.
You can also use the attached savegame (r7237) and start building a port. While there are still wares on the ship, destroy the construction site. The game crashes. This does not happen when all wares and the builder have been unloaded (and the ship drives away) before the construction site is destroyed.

In both cases, I am back on my desktop. There is no error message (or anything useful in stdout/stderr).

[1] https://wl.widelands.org/forum/topic/1570/

[Hans Joachim Desserud (hjd)]

Thanks for reporting this.

I was able to reproduce this issue based on the attached save game and your instructions in r7240. I got the attached backtrace on Ubuntu.

I guess the problem is that the ship is still trying to unload its cargo, but the wares have no where to go anymore. (I wonder whether this can potentially also be triggered if you destroy the target port while the ship is unloading when doing normal ware transportation.)

[TiborB (tiborb95)]

Well, I can imagine the change in code: if a port is not there, do not unload wares, but set itself to EXP_WAITING state and send a message 'Port is probably gone, waiting for new orders'.

But entire shipping stuff is quite complicated, I do not understand it fully....

Anyway, if nobody else, I will look at it....

[wl-zocker (wl-zocker)]

Some of the wares might have been unloaded, and with the remaining wares, no other port can be built. The ship would therefore have to return to the starting/nearest port (similar to "Cancel expedition"). There it could either
- be refilled so that the player can start another expedition
- be emptied.

I prefer option 1, because the player might want to build a port somewhere else. If he does not want that, cancelling the expedition is probably faster than emptying the ship first and then starting a new expedition.

[TiborB (tiborb95)]

I think no wares are unloaded at all. 'assert(baim)' throws an exemption before transferring of wares starts.

[wl-zocker (wl-zocker)]

Start building a port. Some wares will be unloaded because the game does not know what is going to happen. Destroy the in-construction port. The already unloaded wares are lost, the others remain on the ship. For example, you now have a builder, a quartz, a diamond and two gold on the ship, which is not enough to build another port. When the ship attemps to unload the *next* ware, the crash occurs.

[TiborB (tiborb95)]

I believed that all wares are unloaded at once, all right then...

[TiborB (tiborb95)]

I am getting crash on current trunk:

Game: Writing Preload Data ...
Program received signal SIGSEGV, Segmentation fault.
0x08b60a2d in Widelands::GamePreloadPacket::write (this=0xbfffd974, fs=..., game=...)
    at /var/widelands/trunk/src/game_io/game_preload_packet.cc:117
117 s.set_int("gametype", static_cast<int32_t>(game.game_controller()->get_game_type()));

is it known problem?

[Tino (tino79)]

Yes, i experience crashes at the same code point.
I've opened a bug report: https://bugs.launchpad.net/widelands/+bug/1388829

[TiborB (tiborb95)]

I achieved something. Ships returns to a port and unloads, but warehouse window gets into inconsistent state.

Other alternative is that ship stays where it was and user will have to manuali click "cancel expedition". If he instead continues with scouting and tries to build a port elsewhere, port is not finished and the ship is again in some inconsistent status.

[wl-zocker (wl-zocker)]

> Ships returns to a port and unloads, but warehouse window gets into inconsistent state.

There is bug 1191556. Maybe related?

> Other alternative is that ship stays where it was and user will have to manuali click "cancel expedition".

Since the ship cannot do anything else, I consider this micro-management. Better send a message that there were problems and the ship will return to a port.

> If he instead continues with scouting and tries to build a port elsewhere, port is not finished and the ship is again in some inconsistent status.

I think such a case (unfinished port) is very difficult to handle, therefore I did not mention this option.

[TiborB (tiborb95)]

wl-zocker, I think your description in https://bugs.launchpad.net/widelands/+bug/1191556/comments/4 fits.

Except this, I think I have it, a ship returns to port and unloads properly.

I have it in seafaring-ai as by now (not pushed up by now), because trunk is broken anyway so it would not be test-able in I created new branch from it.

[SirVer (sirver)]

There are already a bunch of tests for seafaring, this sounds like it is easily testable too. That should make fixing it easier.

[TiborB (tiborb95)]

should be merged as a part of seafaring-ai branch - revision 7399

[GunChleoc (gunchleoc)]

Fixed in build19-rc1.