Instructions reordering

Instructions types	C#	x86	C# volatile
LoadStore	✔️	❌	❌
LoadLoad	✔️	❌	❌
StoreStore	❌	❌	❌
StoreLoad	✔️	✔️	✔️

Fencing

Full fence

publicvoidMethod(){
...instruction ...
...instruction ...
...instruction ...Thread.MemoryBarrier();-----------------
...instruction ...
...instruction ...
...instruction ...}

Half fence : volatile read : acquire fence

💡 ARF = Acquire Read Follow

privatevolatileint_value;publicvoidMethod(){
...instruction ...
...instruction ...
...instruction ...if(_value)-----------------{
...}
...instruction ...
...instruction ...
...instruction ...}

Half fence : volative write : release fence

privatevolatileint_value;publicvoidMethod(){
...instruction ...
...instruction ...
...instruction ..._value=1;-----------------
...instruction ...
...instruction ...
...instruction ...}

Example

publicclassX{privatevolatileint_continue;publicvoidRun(){_continue=0;while(_continue==0){
...}}publicvoidStop(){_continue=1;}}

In this case if _continue is not defined as volatile and if Run() and Stop() are called from different threads and if the compiler wants to reorder some lines or if CPU wants to reorder the instructions we can have something like this :

publicclassX{privateint_continue;publicvoidRun(){_continue=0;if(_continue!=0)return;while(true){
...}}publicvoidStop(){_continue=1;}}