Atomic Counters in Lua

Here’s the translation of the atomic counters example from Go to Lua, formatted in Markdown suitable for Hugo:

Our primary mechanism for managing state in Lua is through shared variables. However, when dealing with concurrent operations, we need to be careful about race conditions. In this example, we’ll look at using atomic operations for counters accessed by multiple threads.

local lanes = require("lanes").configure()

-- We'll use a shared variable to represent our counter
local ops = lanes.linda()
ops:set("count", 0)

-- A function to increment the counter
local function incrementCounter()
    for i = 1, 1000 do
        -- To atomically increment the counter we use linda:update
        ops:update("count", function(count) return count + 1 end)
    end
end

-- We'll start 50 threads that each increment the counter exactly 1000 times
local threads = {}
for i = 1, 50 do
    threads[i] = lanes.gen("*", incrementCounter)()
end

-- Wait until all the threads are done
for _, thread in ipairs(threads) do
    thread:join()
end

-- Here no threads are writing to 'ops', but it's safe to read the value
local finalCount = ops:get("count")
print("ops:", finalCount)

To run this program, you’ll need to install the Lua Lanes library, which provides multi-threading capabilities for Lua. You can install it using LuaRocks:

$ luarocks install lanes

Then, you can run the program:

$ lua atomic-counters.lua
ops: 50000

We expect to get exactly 50,000 operations. If we had used a non-atomic operation to increment the counter, we’d likely get a different number, changing between runs, because the threads would interfere with each other.

In this Lua implementation:

1. We use the Lanes library to handle multi-threading, as Lua doesn’t have built-in support for threads.
2. We use a Linda object (provided by Lanes) as a shared memory space between threads.
3. The update method of Linda allows us to perform atomic operations on shared values.
4. We create 50 threads, each running the incrementCounter function 1000 times.
5. We wait for all threads to complete using thread:join().
6. Finally, we retrieve and print the final count.

This approach ensures thread-safe increments of our counter, similar to the atomic operations in the original example.