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Emergeblocks: Fix occasional crash
Modification of the emergeblocks internal state was not protected
by a lock, causing a race condition.
This can be reproduced by repeatedly running emergeblocks for an
already-generated section of the map (with multiple emerge threads).
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Rogier-5 authored and paramat committed Oct 16, 2016
1 parent adad6e0 commit 4b17105dc45976e399dab68f85b3030fa27f0ae2
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Showing 2 changed files with 7 additions and 1 deletion.
@@ -212,11 +212,13 @@ void ScriptApiEnv::on_emerge_area_completion(
{
Server *server = getServer();

// This function should be executed with envlock held.
// The caller (LuaEmergeAreaCallback in src/script/lua_api/l_env.cpp)
// should have obtained the lock.
// Note that the order of these locks is important! Envlock must *ALWAYS*
// be acquired before attempting to acquire scriptlock, or else ServerThread
// will try to acquire scriptlock after it already owns envlock, thus
// deadlocking EmergeThread and ServerThread
MutexAutoLock envlock(server->m_env_mutex);

SCRIPTAPI_PRECHECKHEADER

@@ -137,6 +137,10 @@ void LuaEmergeAreaCallback(v3s16 blockpos, EmergeAction action, void *param)
assert(state->script != NULL);
assert(state->refcount > 0);

// state must be protected by envlock
Server *server = state->script->getServer();
MutexAutoLock envlock(server->m_env_mutex);

state->refcount--;

state->script->on_emerge_area_completion(blockpos, action, state);

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