Random freezes in Mineclone 2 0.77

[x2048]

Minetest version

Minetest 5.6.0-dev-debug-a2bf3a2aa (Linux)
Using Irrlicht 1.9.0mt7
Using LuaJIT 2.1.0-beta3
BUILD_TYPE=Debug
RUN_IN_PLACE=1
USE_CURL=1
USE_GETTEXT=0
USE_SOUND=1
STATIC_SHAREDIR="."

OS / Hardware

Operating system: KDE Neon / Ubuntu 20.04
CPU: AMD Ryzen 7

GPU model: AMD Renoir
OpenGL version: 4.5

Summary

When running Mineclone 2 version 0.77, the rendering thread randomly freezes.

Steps to reproduce

1. Install Mineclone 2 version 0.77
2. Start a new survival world, mapgen v7
3. Hold AUX1 (Run) and keep pressing and releasing forward
4. At some point the game will freeze for a few seconds.
   Notice Time-non-rendering below:
   

[x2048]

Narrowed down to ParticleManager::step():

Patch:

diff --git a/src/client/game.cpp b/src/client/game.cpp
index c34e3a415..93a10d308 100644
--- a/src/client/game.cpp
+++ b/src/client/game.cpp
@@ -3837,7 +3837,10 @@ void Game::updateFrame(ProfilerGraph *graph, RunStats *stats, f32 dtime,
 	/*
 		Update particles
 	*/
-	client->getParticleManager()->step(dtime);
+	{
+		ScopeProfiler particles(g_profiler, "Particles step", SPT_ADD);
+		client->getParticleManager()->step(dtime);
+	}
 
 	/*
 		Fog

To trigger, hold AUX1 and keep pressing and releasing forward - Mineclone2 will generate 'drift dust' particles at the player's feet.

[x2048]

Collected logs of collisionMoveSimple:

2022-08-02 22:17:21: INFO[Main]:   A_PARTICLES::# collision_infos nodes  . . .   2148x  536.497
2022-08-02 22:17:21: INFO[Main]:   A_PARTICLES::# collision_infos total  . . .   2148x  536.497
2022-08-02 22:17:21: INFO[Main]:   A_PARTICLES::collision [ms]  . . . . . . . .    1x  981
2022-08-02 22:17:21: INFO[Main]:   A_PARTICLES::step [ms]  . . . . . . . . . .     1x  982
2022-08-02 22:17:27: INFO[Main]:   A_PARTICLES::# collision_infos nodes  . . .   137x  117392
2022-08-02 22:17:27: INFO[Main]:   A_PARTICLES::# collision_infos total  . . .   137x  117392
2022-08-02 22:17:27: INFO[Main]:   A_PARTICLES::collision [ms]  . . . . . . . .    1x  6049
2022-08-02 22:17:27: INFO[Main]:   A_PARTICLES::step [ms]  . . . . . . . . . .     1x  6049
2022-08-02 22:17:28: INFO[Main]:   A_PARTICLES::# collision_infos nodes  . . .   100x  22.08
2022-08-02 22:17:28: INFO[Main]:   A_PARTICLES::# collision_infos total  . . .   100x  22.08
2022-08-02 22:17:28: INFO[Main]:   A_PARTICLES::collision [ms] 
2022-08-02 22:17:28: INFO[Main]:   A_PARTICLES::step [ms] 
2022-08-02 22:17:30: INFO[Main]:   A_PARTICLES::# collision_infos nodes  . . .   2352x  21.0357
2022-08-02 22:17:30: INFO[Main]:   A_PARTICLES::# collision_infos total  . . .   2352x  21.0357
2022-08-02 22:17:30: INFO[Main]:   A_PARTICLES::collision [ms]  . . . . . . . .    1x   1
2022-08-02 22:17:30: INFO[Main]:   A_PARTICLES::step [ms]  . . . . . . . . . .     1x   3

Patch to enable this logging:

diff --git a/src/client/particles.cpp b/src/client/particles.cpp
index 818cdc8cc..43d32fd4b 100644
--- a/src/client/particles.cpp
+++ b/src/client/particles.cpp
@@ -32,6 +32,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "nodedef.h"
 #include "client.h"
 #include "settings.h"
+#include "util/timetaker.h"
+#include "profiler.h"
 
 /*
 	Particle
@@ -181,6 +183,7 @@ void Particle::step(float dtime)
 	m_velocity = av*vecSign(m_velocity) + v3f(m_jitter.pickWithin())*dtime;
 
 	if (m_collisiondetection) {
+		ScopeProfiler collision(g_profiler, "A_PARTICLES::collision", SPT_ADD);
 		aabb3f box = m_collisionbox;
 		v3f p_pos = m_pos * BS;
 		v3f p_velocity = m_velocity * BS;
diff --git a/src/collision.cpp b/src/collision.cpp
index 910c80604..1d382e833 100644
--- a/src/collision.cpp
+++ b/src/collision.cpp
@@ -362,6 +362,7 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 	}
 
 	} // tt2
+	g_profiler->avg("A_PARTICLES::# collision_infos nodes", cinfo.size());
 
 	if(collideWithObjects)
 	{
@@ -434,7 +435,7 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 		}
 #endif
 	} //tt3
-
+	g_profiler->avg("A_PARTICLES::# collision_infos total", cinfo.size());
 	/*
 		Collision detection
 	*/

[appgurueu]

Could this be related to @velartrill's "better particles" PR?

[x2048]

Flamegraph during freeze:

[x2048]

Log of velocity and acceleration in collisionMoveSimple()

2022-08-02 23:11:15: INFO[Main]:   A_PARTICLES::velocity  . . . . . . . . . . .  2990x  5.16571
2022-08-02 23:11:26: INFO[Main]:   A_PARTICLES::acceleration  . . . . . . . . .  3531x  56.4033
2022-08-02 23:11:26: INFO[Main]:   A_PARTICLES::velocity  . . . . . . . . . . .  3531x  1.59983e+14
2022-08-02 23:11:40: INFO[Main]:   A_PARTICLES::acceleration  . . . . . . . . .  203x  34.6728
2022-08-02 23:11:40: INFO[Main]:   A_PARTICLES::velocity  . . . . . . . . . . .  203x  inf
2022-08-02 23:11:40: INFO[Main]:   A_PARTICLES::acceleration  . . . . . . . . .  219x  26.6996

[x2048]

Root cause is uninitialized default value for f32 particle parameters such as bounce, which caused particle velocity to become very high after a collision.

Patch that fixes the problem:

diff --git a/src/particles.h b/src/particles.h
index 74bfa7fce..3061deb83 100644
--- a/src/particles.h
+++ b/src/particles.h
@@ -91,7 +91,7 @@ namespace ParticleParamTypes
                using ValType = T;
                using pickFactors = float[PN];
 
-               T val;
+               T val = T();
                using This = Parameter<T, PN>;
 
                Parameter() = default;

Edit: added root cause of the problem.