AFIAK, and I'm not MIPS expert, but I believe it doesn't have the ability to add a value directly to a memory address. You have to do something like
// Not real MIPS, just what I've gleaned from a brief look at some docs
LOAD addr, register
ADD 1, register
STORE register, addr
The LOAD and STORE are atomic, but the `ADD` happens out of band.
That's a problem if any sort of interrupt happens (if you are multi-threading then a possibility). If it happens at the load, then a separate thread can update "addr" which mean the later STORE will stomp on what's there.
x86 and ARM can do
ADD 1, addr
as well as other instructions like "compare and swap"
LOAD addr, register
MOV register, register2
ADD 1, register2
COMPARE_AND_SWAP addr, register, register2
if (cas_failed) { try again }
alt Hacker News
AFIAK, and I'm not MIPS expert, but I believe it doesn't have the ability to add a value directly to a memory address. You have to do something like
The LOAD and STORE are atomic, but the `ADD` happens out of band.That's a problem if any sort of interrupt happens (if you are multi-threading then a possibility). If it happens at the load, then a separate thread can update "addr" which mean the later STORE will stomp on what's there.
x86 and ARM can do
as well as other instructions like "compare and swap"