largest_free_block may walk the free block list but doesn't hold the CodeCache lock while doing so which could cause crashes.

Stack: [0x00007fbcef2e9000,0x00007fbcef3ea000], sp=0x00007fbcef3e8490, free space=1021k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x4ab490] CodeHeap::largest_free_block() const+0x80
V [libjvm.so+0x3a29b7] CompileBroker::compile_method(methodHandle, int, int, methodHandle, int, char const*, Thread*)+0x307
V [libjvm.so+0x39364f] SimpleCompPolicy::method_invocation_event(methodHandle, Thread*)+0xef
V [libjvm.so+0x392b1e] NonTieredCompPolicy::event(methodHandle, methodHandle, int, int, CompLevel, Thread*)+0xde
V [libjvm.so+0x504c4e] InterpreterRuntime::frequency_counter_overflow_inner(JavaThread*, unsigned char*)+0x13e
V [libjvm.so+0x5050c6] InterpreterRuntime::frequency_counter_overflow(JavaThread*, unsigned char*)+0x16
j org.sunflow.core.renderer.BucketRenderer.refineSamples([Lorg/sunflow/core/renderer/BucketRenderer$ImageSample;IIIIFLorg/sunflow/core/IntersectionState;)V+0
j org.sunflow.core.renderer.BucketRenderer.refineSamples([Lorg/sunflow/core/renderer/BucketRenderer$ImageSample;IIIIFLorg/sunflow/core/IntersectionState;)V+241
j org.sunflow.core.renderer.BucketRenderer.renderBucket(Lorg/sunflow/core/Display;IIILorg/sunflow/core/IntersectionState;)V+454
j org.sunflow.core.renderer.BucketRenderer.access$300(Lorg/sunflow/core/renderer/BucketRenderer;Lorg/sunflow/core/Display;IIILorg/sunflow/core/IntersectionState;)V+8
j org.sunflow.core.renderer.BucketRenderer$BucketThread.run()V+125
v ~StubRoutines::call_stub
V [libjvm.so+0x509ad5] JavaCalls::call_helper(JavaValue*, methodHandle*, JavaCallArguments*, Thread*)+0x345
V [libjvm.so+0x508608] JavaCalls::call(JavaValue*, methodHandle, JavaCallArguments*, Thread*)+0x28
V [libjvm.so+0x50889c] JavaCalls::call_virtual(JavaValue*, KlassHandle, Symbol*, Symbol*, JavaCallArguments*, Thread*)+0x17c
V [libjvm.so+0x5089c7] JavaCalls::call_virtual(JavaValue*, Handle, KlassHandle, Symbol*, Symbol*, Thread*)+0x47
V [libjvm.so+0x5577ff] thread_entry(JavaThread*, Thread*)+0xdf
V [libjvm.so+0x7fdf4a] JavaThread::run()+0x17a
V [libjvm.so+0x6e2590] java_start(Thread*)+0x100