50 lines
2.2 KiB
Markdown
50 lines
2.2 KiB
Markdown
# Impotent
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This is an attempt to create a Lua virtual machine capable of true multithreading. Once the nctref compiler matures enough, I intend to plug it into Impotent as a JIT.
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Completed features:
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1. Per-thread heap /w special heap for exited threads called the "dead heap"
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2. Naive mark & sweep GC
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3. Completely thread-safe, including lock-free implementation for tables
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Impotent is still work-in-progress:
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1. Integers are 32-bit only
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2. No error handling, meaning any mistake will either crash the VM or make it silently fail
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3. The only standard library is `print` and it doesn't work correctly
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4. Tables cannot be resized
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5. Most operators are still missing
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6. The user API is completely different from that of PoC Lua
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7. Being lock-free, tables are not split to "array" and "hash" parts
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8. Userdata is not yet supported.
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Impotent requires C11 and an architecture with 8-byte atomic operations, but otherwise it is completely cross-platform.
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Performance-wise, it's surprisingly competitive with PoC Lua, considering how quickly it was made up to the point of writing this README (~2 weeks). By far the worst bottleneck is the GC, since it requires all threads and their heaps to synchronize.
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Certain Lua idioms become impossible under Impotent. For example the idiom of appending to tables (`t[#t + 1] = x`) isn't atomic, therefore `table.insert` should be used instead.
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## Additions
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Obviously, threading. Any thread can access any value from any other thread, including for reading or writing. Operations such as getting or setting are lock-free in the best case scenario, but other operations (such as the `#` operator) must lock the table temporarily.
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Besides this, I have no intent to greatly deviate from standard Lua, to keep source-level compatibility as best I can. The only addition to the standard library is the `threads` global, with two methods as of now.
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### `threads.run`
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Runs a function in a newly created thread. Does not block the caller.
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threads.run(function()
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-- Do something expensive
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end)
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### `threads.parallel`
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Runs a function in n parallel threads. Blocks the caller until all threads finish.
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threads.parallel(8, function()
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-- Do something parallelizable.
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end)
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