Initial, untested version of controller and worker

Worker has been tested to a marginal extent, but the controller is
litereally untested.

22 files changed, 1662 insertions, 0 deletions

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diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..f6a5141
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,3 @@
+[workspace]
+
+members = ["worker", "controller", "utils"]
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..256ecd2
--- /dev/null
+++ b/README.md
@@ -0,0 +1,92 @@
+# Distributed computing
+
+A framework for distributed computing -- that is, running jobs across multiple
+machines.
+
+## Compute core API version 1
+
+Functions that should be exposed, without mangling, by the compute core `.so`
+library:
+
+- `int32_t worker_init(int32_t version)`
+  - Will be called when initialising the library. The integer argument is the
+    version of this API specification; the library should check that it is
+    equal to the expected value.
+
+    Should return 0 on successful initialisation, or nonzero if an error
+    occurred.
+
+- `int32_t worker_run_job(uint64_t size, void *data, uint64_t *outsize, void **outdata)`
+  - Run a job. The job data is specified in the data blob pointed to by `data`,
+    which is `size` bytes in size. The worker is allowed to modify the memory
+    behind `data` during execution of this function, but the memory will be
+    deallocated as soon as `worker_run_job` returns.
+
+    A pointer to memory containing the computed results should be stored in
+    `outdata`, and its size in `outsize`. When the memory allocated for the
+    output data may be freed, `worker_free_outdata` will be called. If there
+    is no data to return, for example because an error occurred, store 0 in
+    `outsize` and a null pointer in `outdata`.
+
+    Should return 0 on successful execution, or nonzero if an error occurred.
+
+- `void worker_free_outdata(uint64_t size, void *outdata)`
+  - Free memory allocated for the output data of a job. This is called when the
+    memory for the output data of the last job is no longer needed, and will
+    always be called before the next job is started.
+
+Note that there is no function called before unloading the library. If you need
+such a thing, please use [destructors][1], or unload necessary things in
+`worker_free_outdata`.
+
+## Worker socket protocol version 1
+
+All integers in the below description are little-endian.
+
+Common data types used in the message descriptions below:
+- **String**/**Blob**: 8-byte unsigned integer indicating the length of
+  the data, then that many bytes making up the string or blob. A string is
+  valid UTF-8, while a blob can contain arbitrary data.
+
+A **message from controller to worker** has the following format:
+- Message type [1 byte]
+- ID [8 bytes]
+- Payload length [8-byte unsigned integer]
+- Payload [variable length and contents]
+
+A **response from worker to controller** has the following format:
+- Response type [1 byte]
+- ID of message replied to [8 bytes]
+- Payload length [8-byte unsigned integer]
+- Payload [variable length and contents]
+
+The possible **response types** are the following:
+- `0x01`: Successful response to a message, as described in the table of
+  message types.
+- `0xff`: An error response; something went wrong. The entire payload is an
+  UTF-8 error message.
+
+The possible **message types** are the following:
+
+- `0x01`: Version exchange
+  - Payload: 4-byte unsigned integer, the protocol version of the
+    server. In this version, this is 1.
+  - Successful response: 1 byte, 1 if the version is accepted by the worker, 0
+	if not. If the version is not accepted, the connection is closed by both
+	sides.
+
+- `0x02`: New compute core
+  - Payload: A string giving the name of the compute core, then a blob giving
+	the contents of a dynamic library file that can be loaded at runtime, e.g.
+	a `.so` file. This library will be loaded as the compute core for the
+	worker.
+  - Successful response: Empty.
+
+- `0x03`: New job
+  - Payload: An 8-byte unsigned integer giving the ID of the job, then a blob
+    giving the input data for the compute core.
+  - Successful response: A 4-byte signed integer giving the exit code of the
+	job as returned by the compute core, then a blob giving the output data.
+
+
+[1]: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-destructor-function-attribute
diff --git a/controller/Cargo.toml b/controller/Cargo.toml
new file mode 100644
index 0000000..319e1b7
--- /dev/null
+++ b/controller/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "dd-controller"
+version = "0.1.0"
+authors = ["Tom Smeding <tom.smeding@gmail.com>"]
+edition = "2018"
+
+[dependencies]
+tokio = { version = "0.2", features = ["full"] }
+dd-utils = { path = "../utils" }
diff --git a/controller/src/lib.rs b/controller/src/lib.rs
new file mode 100644
index 0000000..ee02b3b
--- /dev/null
+++ b/controller/src/lib.rs
@@ -0,0 +1,492 @@
+use std::collections::{HashMap, VecDeque};
+use std::convert::TryInto;
+use std::io::{self, ErrorKind};
+use std::net::Shutdown;
+use std::sync::Arc;
+use std::thread;
+use tokio::io::{AsyncReadExt, AsyncWriteExt, WriteHalf};
+use tokio::net::{TcpListener, TcpStream};
+use tokio::runtime;
+use tokio::task;
+use tokio::sync::{mpsc, oneshot, Mutex};
+use dd_utils::error::*;
+use dd_utils::idgen::IdGen;
+use dd_utils::protocol::*;
+use dd_utils::read_ext::ReadExt;
+
+async fn send_vectored(
+    writer: &mut (impl AsyncWriteExt + Unpin),
+    typ: u8,
+    id: u64,
+    payload: &[impl AsRef<[u8]>]
+) -> io::Result<()> {
+    let mut header = [0u8; 17];
+    header[0] = typ;
+    header[1..9].copy_from_slice(&id.to_le_bytes());
+    let sumlen: usize = payload.iter().map(|v| v.as_ref().len()).sum();
+    header[9..17].copy_from_slice(&sumlen.to_le_bytes());
+    writer.write_all(&header).await?;
+    for part in payload {
+        writer.write_all(part.as_ref()).await?;
+    }
+    Ok(())
+}
+
+async fn receive_message(reader: &mut (impl AsyncReadExt + Unpin))
+        -> io::Result<Option<RawMessage>> {
+    let mut header = [0u8; 17];
+    if let Err(e) = reader.read(&mut header).await {
+        if e.kind() == ErrorKind::UnexpectedEof { return Ok(None); }
+        else { return Err(e); }
+    }
+
+    let typ = header[0];
+    let id = u64::from_le_bytes(header[1..9].try_into().unwrap());
+    let length = usize::from_le_bytes(header[9..17].try_into().unwrap());
+
+    let mut payload = Vec::new();
+    payload.resize(length, 0u8);
+    if let Err(e) = reader.read(&mut payload).await {
+        if e.kind() == ErrorKind::UnexpectedEof { return Ok(None); }
+        else { return Err(e); }
+    }
+
+    Ok(Some(RawMessage { typ, id, payload }))
+}
+
+fn encode_message(msg: MessageBody) -> Vec<Vec<u8>> {
+    let mut payload = Vec::new();
+
+    match msg {
+        MessageBody::Version(version) => {
+            payload.push(version.to_le_bytes().to_vec());
+        }
+
+        MessageBody::NewCore(name, libfile) => {
+            payload.push(name.len().to_le_bytes().to_vec());
+            payload.push(name.into_bytes());
+            payload.push(libfile.len().to_le_bytes().to_vec());
+            payload.push(libfile);
+        }
+
+        MessageBody::Job(jobid, input) => {
+            payload.push(jobid.to_le_bytes().to_vec());
+            payload.push(input.len().to_le_bytes().to_vec());
+            payload.push(input);
+        }
+    }
+
+    payload
+}
+
+#[derive(Debug)]
+pub struct CompletionEvent {
+    pub jobid: u64,
+    pub result: Result<(i32, Vec<u8>), String>,
+}
+
+#[derive(Debug)]
+enum Inbound {
+    Completion(CompletionEvent),
+}
+
+#[derive(Debug)]
+enum Outbound {
+    NewCore(String, Vec<u8>),
+    NewJob(u64, Vec<u8>),
+    NumWorkers(oneshot::Sender<u64>),
+    Quit,
+}
+
+pub struct ComputePool {
+    runtime: runtime::Runtime,
+
+    iothread: Option<thread::JoinHandle<()>>,
+    inbound: mpsc::UnboundedReceiver<Inbound>,
+    outbound: mpsc::Sender<Outbound>,
+
+    // The number of jobs for which the completion event has not yet been consumed
+    num_running: u64,
+}
+
+#[derive(Debug)]
+enum ThreadCollect {
+    NewWorker(TcpStream, u64),  // Worker socket, and next unused message id
+    WorkerReady(u64),  // Worker id (indicates that this worker has its core initialised)
+    Query(Outbound),
+    Completion(u64, CompletionEvent),  // Worker id, and event
+}
+
+async fn thread_handshake_handler(mut listener: TcpListener, sink: mpsc::Sender<ThreadCollect>) {
+    loop {
+        let (mut sock, _) = listener.accept().await.expect("Accept failed on TCP server socket");
+        let mut sink = sink.clone();
+        task::spawn(async move {
+            let payload = encode_message(MessageBody::Version(1));
+            if send_vectored(&mut sock, 1, 1, &payload).await.is_err() {
+                match sock.shutdown(Shutdown::Both) {
+                    Ok(()) => {}
+                    Err(_) => {}  // explicitly ignore errors here, we're closing anyway
+                }
+                return;
+            }
+
+            match receive_message(&mut sock).await {
+                Ok(Some(rawmsg)) if rawmsg.typ == 1 && rawmsg.id == 1 &&
+                                    rawmsg.payload.len() == 1 &&
+                                    rawmsg.payload[0] == 1
+                => {
+                    sink.send(ThreadCollect::NewWorker(sock, 2)).await.unwrap();
+                }
+
+                _ => {
+                    match sock.shutdown(Shutdown::Both) {
+                        Ok(()) => {}
+                        Err(_) => {}  // explicitly ignore errors here, we're closing anyway
+                    }
+                }
+            }
+        });
+    }
+}
+
+async fn thread_query_handler(
+    mut chan: mpsc::Receiver<Outbound>,
+    mut sink: mpsc::Sender<ThreadCollect>
+) {
+    loop {
+        if let Some(msg) = chan.recv().await {
+            sink.send(ThreadCollect::Query(msg)).await.unwrap();
+        } else {
+            return;
+        }
+    }
+}
+
+struct Worker {
+    socket: WriteHalf<TcpStream>,
+    msg_idgen: IdGen,
+    loaded_core: u64,
+    handler_map: Arc<Mutex<HashMap<u64, Box<dyn FnOnce(u64, RawMessage) + Send>>>>,
+}
+
+impl Worker {
+    fn new(worker_id: u64, next_msg_id: u64, socket: TcpStream) -> Self {
+        let (mut read_half, write_half) = tokio::io::split(socket);
+        let worker = Worker {
+            socket: write_half,
+            msg_idgen: IdGen::new(next_msg_id),
+            loaded_core: 0,
+            handler_map: Arc::new(Mutex::new(HashMap::new())),
+        };
+
+        {
+            let handler_map = worker.handler_map.clone();
+            task::spawn(async move {
+                loop {
+                    let rawmsg = match receive_message(&mut read_half).await {
+                        Ok(Some(rawmsg)) => rawmsg,
+                        _ => break,
+                    };
+
+                    let mut handler_map = handler_map.lock().await;
+                    match handler_map.remove(&rawmsg.id) {
+                        Some(handler) => handler(worker_id, rawmsg),
+                        None => {
+                            eprintln!("Warning: no handler found for worker reply id {}", rawmsg.id);
+                        }
+                    }
+                }
+            });
+        }
+
+        worker
+    }
+
+    /// Returns whether the send succeeded. In case of failure, the handler is not registered.
+    async fn send(
+        &mut self,
+        typ: u8,
+        payload: &[impl AsRef<[u8]>],
+        handler: impl FnOnce(u64, RawMessage) + Send + 'static
+    ) -> bool {
+        let msgid = self.msg_idgen.gen();
+        self.handler_map.lock().await.insert(msgid, Box::new(handler));
+        match send_vectored(&mut self.socket, typ, msgid, &payload).await {
+            Ok(()) => true,
+            Err(_) => {
+                self.handler_map.lock().await.remove(&msgid);
+                false
+            }
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Job {
+    id: u64,
+    input: Vec<u8>,
+}
+
+#[derive(Debug, Clone)]
+struct ComputeCore {
+    name: String,
+    libfile: Vec<u8>,
+}
+
+/// Returns whether job was successfully sent to the worker
+async fn worker_run_job(
+    worker: &mut Worker,
+    job: Job,
+    mut result_chan: mpsc::Sender<ThreadCollect>
+) -> bool {
+    let Job { id: jobid, input } = job;
+    let payload = encode_message(MessageBody::Job(jobid, input));
+    let handler = move |wid: u64, rawmsg: RawMessage| {
+        task::spawn(async move {
+            let result = if rawmsg.typ == 1 {
+                let mut reader: &[u8] = &rawmsg.payload;
+                if let Some(retval) = reader.read_le_i32() {
+                    if let Some(output) = reader.read_pascal_blob() {
+                        Ok((retval, output.to_vec()))
+                    } else {
+                        Err("<Invalid reply format!>".to_string())
+                    }
+                } else {
+                    Err("<Invalid reply format!>".to_string())
+                }
+            } else {
+                Err(String::from_utf8_lossy(&rawmsg.payload).to_string())
+            };
+
+            let event = ThreadCollect::Completion(
+                wid,
+                CompletionEvent { jobid, result }
+            );
+            result_chan.send(event).await.unwrap();
+        });
+    };
+
+    worker.send(3, &payload, handler).await
+}
+
+/// Returns whether the message was successfully sent to the worker.
+async fn worker_set_new_core(
+    worker: &mut Worker,
+    new_core_id: u64,
+    core: ComputeCore,
+    workers_map: Arc<Mutex<HashMap<u64, Worker>>>,
+    result_chan: mpsc::Sender<ThreadCollect>
+) -> bool {
+    worker_set_new_core_payload(
+        worker,
+        new_core_id,
+        &encode_message(MessageBody::NewCore(core.name, core.libfile)),
+        workers_map,
+        result_chan
+    ).await
+}
+
+/// Returns whether the message was successfully sent to the worker.
+async fn worker_set_new_core_payload(
+    worker: &mut Worker,
+    new_core_id: u64,
+    payload: &[impl AsRef<[u8]>],
+    workers_map: Arc<Mutex<HashMap<u64, Worker>>>,
+    mut result_chan: mpsc::Sender<ThreadCollect>
+) -> bool {
+    let handler = move |wid: u64, rawmsg: RawMessage| {
+        task::spawn(async move {
+            if rawmsg.typ == 1 {
+                if let Some(worker) = workers_map.lock().await.get_mut(&wid) {
+                    worker.loaded_core = new_core_id;
+                    result_chan.send(ThreadCollect::WorkerReady(wid)).await.unwrap();
+                }
+            } else {
+                eprintln!("Worker {} could not load new core:\n{}",
+                          wid, String::from_utf8_lossy(&rawmsg.payload));
+            }
+        });
+    };
+    worker.send(2, payload, handler).await
+}
+
+// IO thread:
+// - waits for worker connections
+// - has a channel open to the parent thread on which it receives commands to send to workers
+// - receives responses from workers and puts those on the channel
+fn thread_entry(
+    listen_port: u16,
+    query_chan: mpsc::Receiver<Outbound>,
+    event_chan: mpsc::UnboundedSender<Inbound>
+) {
+    runtime::Runtime::new().unwrap().block_on(async {
+        let (mut collector_sink, mut collector_source) = mpsc::channel(10);
+        let listener = TcpListener::bind(("0.0.0.0", listen_port)).await.unwrap();
+
+        task::spawn(thread_handshake_handler(listener, collector_sink.clone()));
+        task::spawn(thread_query_handler(query_chan, collector_sink.clone()));
+
+        let mut worker_idgen = IdGen::new(1);
+
+        let workers: Arc<Mutex<HashMap<u64, Worker>>> = Arc::new(Mutex::new(HashMap::new()));
+        let mut free_workers: VecDeque<u64> = VecDeque::new();
+        let mut current_core: Option<ComputeCore> = None;
+        let mut current_core_id: u64 = 0;
+        let mut core_idgen = IdGen::new(1);
+        let mut job_queue: VecDeque<Job> = VecDeque::new();
+
+        loop {
+            let message = match collector_source.recv().await {
+                Some(message) => message,
+                None => break,
+            };
+
+            match message {
+                ThreadCollect::Query(Outbound::NewCore(name, libfile)) => {
+                    let new_core_id = core_idgen.gen();
+                    current_core = Some(ComputeCore { name: name.clone(), libfile: libfile.clone() });
+                    current_core_id = new_core_id;
+
+                    let payload = encode_message(MessageBody::NewCore(name, libfile));
+
+                    let mut workers_locked = workers.lock().await;
+
+                    while let Some(worker_id) = free_workers.pop_front() {
+                        if let Some(worker) = workers_locked.get_mut(&worker_id) {
+                            if !worker_set_new_core_payload(
+                                    worker, new_core_id, &payload, workers.clone(),
+                                    collector_sink.clone()).await {
+                                workers_locked.remove(&worker_id);
+                            }
+                        }
+                    }
+                }
+
+                ThreadCollect::Query(Outbound::NewJob(jobid, input)) => {
+                    job_queue.push_back(Job { id: jobid, input });
+                }
+
+                ThreadCollect::Query(Outbound::NumWorkers(chan)) => {
+                    chan.send(workers.lock().await.len() as u64).unwrap();
+                }
+
+                ThreadCollect::Query(Outbound::Quit) => {
+                    break;
+                }
+
+                ThreadCollect::Completion(worker_id, event) => {
+                    event_chan.send(Inbound::Completion(event)).unwrap();
+                    collector_sink.send(ThreadCollect::WorkerReady(worker_id)).await.unwrap();
+                }
+
+                ThreadCollect::NewWorker(socket, next_msg_id) => {
+                    let wid = worker_idgen.gen();
+                    let worker = Worker::new(wid, next_msg_id, socket);
+
+                    workers.lock().await.insert(wid, worker);
+
+                    // Delegate the core setup to the WorkerReady event
+                    collector_sink.send(ThreadCollect::WorkerReady(wid)).await.unwrap();
+                }
+
+                ThreadCollect::WorkerReady(worker_id) => {
+                    let mut workers_locked = workers.lock().await;
+
+                    if let Some(worker) = workers_locked.get_mut(&worker_id) {
+                        if worker.loaded_core != current_core_id {
+                            let current_core = current_core.unwrap().clone();
+                            worker_set_new_core(
+                                worker, current_core_id, current_core, workers.clone(),
+                                collector_sink.clone()
+                            ).await;
+                            return;
+                        }
+
+                        free_workers.push_back(worker_id);
+                    }
+                }
+            }
+
+            if job_queue.len() > 0 && free_workers.len() > 0 {
+                let job = job_queue.pop_front().unwrap();
+                let mut workers_locked = workers.lock().await;
+
+                // Loop until a worker exists and is functional
+                loop {
+                    let worker_id = free_workers.pop_front().unwrap();
+                    if let Some(worker) = workers_locked.get_mut(&worker_id) {
+                        let result_chan = collector_sink.clone();
+                        if !worker_run_job(worker, job.clone(), result_chan).await {
+                            workers_locked.remove(&worker_id);
+                        } else {
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+    });
+}
+
+/// Will call ComputePool::close(), `unwrap`-ing the result.
+impl Drop for ComputePool {
+    fn drop(&mut self) {
+        self.close().unwrap();
+    }
+}
+
+impl ComputePool {
+    pub fn new(port: u16) -> io::Result<Self> {
+        // Spawn the IO thread
+        let (inbound_sender, inbound_receiver) = mpsc::unbounded_channel();
+        let (outbound_sender, outbound_receiver) = mpsc::channel(1);
+        let jh = thread::spawn(move || { thread_entry(port, outbound_receiver, inbound_sender) });
+        Ok(ComputePool {
+            runtime: runtime::Runtime::new()?,
+            iothread: Some(jh),
+            inbound: inbound_receiver,
+            outbound: outbound_sender,
+            num_running: 0,
+        })
+    }
+
+    pub fn close(&mut self) -> io::Result<()> {
+        self.runtime.block_on(self.outbound.send(Outbound::Quit)).iores()?;
+        self.iothread.take().map(|jh| jh.join().unwrap());
+        Ok(())
+    }
+
+    pub fn set_core(&mut self, name: String, libfile: Vec<u8>) -> io::Result<()> {
+        // Instruct the IO thread to send the core to all workers, and also set it on every new
+        // worker that arrives
+        self.runtime.block_on(self.outbound.send(Outbound::NewCore(name, libfile))).iores()
+    }
+
+    pub fn current_job_parallelism(&mut self) -> io::Result<u64> {
+        // Query the IO thread for the number of workers currently registered
+        let mut outbound = self.outbound.clone();
+        self.runtime.block_on(async {
+            let (sender, receiver) = oneshot::channel();
+            outbound.send(Outbound::NumWorkers(sender)).await.iores()?;
+            receiver.await.iores()
+        })
+    }
+
+    pub fn submit_job(&mut self, jobid: u64, input: Vec<u8>) -> io::Result<()> {
+        // Send the job to the IO thread, which will send it to a round-robin worker
+        self.runtime.block_on(self.outbound.send(Outbound::NewJob(jobid, input))).iores()
+    }
+
+    pub fn next_completion_event(&mut self) -> io::Result<Option<CompletionEvent>> {
+        // If the counter is still positive, wait for events from the IO thread
+        if self.num_running > 0 {
+            match self.runtime.block_on(self.inbound.recv()) {
+                Some(Inbound::Completion(event)) => Ok(Some(event)),
+                None => Err("IO thread unexpectedly quit".ioerr()),
+            }
+        } else {
+            Ok(None)
+        }
+    }
+}
diff --git a/examples/.gitignore b/examples/.gitignore
new file mode 100644
index 0000000..140f8cf
--- /dev/null
+++ b/examples/.gitignore
@@ -0,0 +1 @@
+*.so
diff --git a/examples/kaas/Makefile b/examples/kaas/Makefile
new file mode 100644
index 0000000..e7d5154
--- /dev/null
+++ b/examples/kaas/Makefile
@@ -0,0 +1,9 @@
+.PHONY: all clean
+
+all: kaas.so
+
+clean:
+	rm -f kaas.so
+
+kaas.so: kaas.c
+	gcc -Wall -Wextra -fPIC -shared $< -o $@
diff --git a/examples/kaas/kaas.c b/examples/kaas/kaas.c
new file mode 100644
index 0000000..f823442
--- /dev/null
+++ b/examples/kaas/kaas.c
@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+
+__attribute__((constructor))
+void constr() {
+	printf("kaas: constructor!\n");
+}
+
+__attribute__((destructor))
+void destr() {
+	printf("kaas: destructor!\n");
+}
+
+int worker_init(int version) {
+	printf("kaas: initialised with version %d\n", version);
+	return 0;
+}
+
+int worker_run_job(size_t size, void *input_, size_t *outsize, void **outputp) {
+	const char *input = input_;
+	char *output = malloc(size);
+	for (size_t i = 0; i < size; i++) output[i] = toupper(input[i]);
+	*outsize = size;
+	*outputp = output;
+	return 0;
+}
+
+void worker_free_outdata(size_t size, void *data) {
+	(void)size;
+	free(data);
+}
diff --git a/examples/mandel/Makefile b/examples/mandel/Makefile
new file mode 100644
index 0000000..4311ee9
--- /dev/null
+++ b/examples/mandel/Makefile
@@ -0,0 +1,9 @@
+.PHONY: all clean
+
+all: mandel.so
+
+clean:
+	rm -f mandel.so
+
+mandel.so: mandel.c
+	gcc -Wall -Wextra -fPIC -shared -O3 -fopenmp $< -o $@
diff --git a/examples/mandel/mandel.c b/examples/mandel/mandel.c
new file mode 100644
index 0000000..f7517ba
--- /dev/null
+++ b/examples/mandel/mandel.c
@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+struct input {
+	double ltx, lty;
+	double rbx, rby;
+	size_t width, height;
+	size_t maxiter;
+};
+
+int worker_init(int version) {
+	fprintf(stderr, "mandel: init(%d)\n", version);
+	return version == 1 ? 0 : 1;
+}
+
+int worker_run_job(size_t inputsize, const void *input_, size_t *outputsize, void **outputp) {
+	if (inputsize != sizeof(struct input)) {
+		fprintf(stderr, "mandel: Input has invalid size %zu (expected %zu)\n", inputsize, sizeof(struct input));
+		return -1;
+	}
+
+	fprintf(stderr, "mandel: run_job()\n");
+
+	const struct input *const input = input_;
+
+	*outputsize = 4 * input->width * input->height;
+	uint32_t *const output = *outputp = malloc(*outputsize);
+
+#pragma omp parallel for
+	for (size_t yi = 0; yi < input->height; yi++) {
+		for (size_t xi = 0; xi < input->width; xi++) {
+			const double y = (input->rby - input->lty) / (input->height - 1) * yi;
+			const double x = (input->rbx - input->ltx) / (input->width - 1) * xi;
+
+			double a = x, b = y, a2 = a * a, b2 = b * b;
+			size_t n;
+			for (n = 0; n < input->maxiter && a2 + b2 < 4; n++) {
+				b = 2 * a * b + y;
+				a = a2 - b2 + x;
+				a2 = a * a; b2 = b * b;
+			}
+
+			output[input->width * yi + xi] = n;
+		}
+	}
+
+	fprintf(stderr, "mandel: run_job() finished\n");
+
+	return 0;
+}
+
+void worker_free_outdata(size_t size, void *output) {
+	(void)size;
+	fprintf(stderr, "mandel: free_outdata()\n");
+	free(output);
+}
diff --git a/utils/Cargo.toml b/utils/Cargo.toml
new file mode 100644
index 0000000..53767d0
--- /dev/null
+++ b/utils/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "dd-utils"
+version = "0.1.0"
+authors = ["Tom Smeding <tom.smeding@gmail.com>"]
+edition = "2018"
+
+[dependencies]
diff --git a/utils/src/enums.rs b/utils/src/enums.rs
new file mode 100644
index 0000000..d08c7ea
--- /dev/null
+++ b/utils/src/enums.rs
@@ -0,0 +1,11 @@
+pub enum MessageBody {
+    Version(u32),
+    NewCore(String, Vec<u8>),
+    Job(u64, Vec<u8>),
+}
+
+pub enum Reply {
+    Version(bool),
+    NewCore,
+    Job(i32, Vec<u8>),
+}
diff --git a/utils/src/error.rs b/utils/src/error.rs
new file mode 100644
index 0000000..f25bc5d
--- /dev/null
+++ b/utils/src/error.rs
@@ -0,0 +1,27 @@
+use std::io;
+
+pub trait IntoIOError {
+    fn ioerr(self) -> io::Error;
+    fn perror(self, parent: io::Error) -> io::Error;
+}
+
+// This impl bound is taken directly from the io::Error::new function.
+impl<E: Into<Box<dyn std::error::Error + Send + Sync>>> IntoIOError for E {
+    fn ioerr(self) -> io::Error {
+        io::Error::new(io::ErrorKind::Other, self)
+    }
+
+    fn perror(self, parent: io::Error) -> io::Error {
+        io::Error::new(parent.kind(), format!("{}: {}", self.into(), parent))
+    }
+}
+
+pub trait IntoIOResult<T> {
+    fn iores(self) -> io::Result<T>;
+}
+
+impl<T, E: IntoIOError> IntoIOResult<T> for Result<T, E> {
+    fn iores(self) -> io::Result<T> {
+        self.map_err(|e| e.ioerr())
+    }
+}
diff --git a/utils/src/idgen.rs b/utils/src/idgen.rs
new file mode 100644
index 0000000..20f13ff
--- /dev/null
+++ b/utils/src/idgen.rs
@@ -0,0 +1,16 @@
+#[derive(Debug)]
+pub struct IdGen {
+    next: u64,
+}
+
+impl IdGen {
+    pub fn new(start: u64) -> Self {
+        IdGen { next: start }
+    }
+
+    pub fn gen(&mut self) -> u64 {
+        let res = self.next;
+        self.next += 1;
+        res
+    }
+}
diff --git a/utils/src/lib.rs b/utils/src/lib.rs
new file mode 100644
index 0000000..867fd97
--- /dev/null
+++ b/utils/src/lib.rs
@@ -0,0 +1,4 @@
+pub mod error;
+pub mod idgen;
+pub mod protocol;
+pub mod read_ext;
diff --git a/utils/src/protocol.rs b/utils/src/protocol.rs
new file mode 100644
index 0000000..4820f79
--- /dev/null
+++ b/utils/src/protocol.rs
@@ -0,0 +1,44 @@
+use std::convert::TryInto;
+use std::io::{self, BufReader, ErrorKind, Read};
+use std::net::TcpStream;
+
+pub enum MessageBody {
+    Version(u32),
+    NewCore(String, Vec<u8>),
+    Job(u64, Vec<u8>),
+}
+
+pub enum Reply {
+    Version(bool),
+    NewCore,
+    Job(i32, Vec<u8>),
+}
+
+pub struct RawMessage {
+    pub typ: u8,
+    pub id: u64,
+    pub payload: Vec<u8>,
+}
+
+impl RawMessage {
+    pub fn receive(reader: &mut BufReader<TcpStream>) -> io::Result<Option<Self>> {
+        let mut header = [0u8; 17];
+        if let Err(e) = reader.read(&mut header) {
+            if e.kind() == ErrorKind::UnexpectedEof { return Ok(None); }
+            else { return Err(e); }
+        }
+
+        let typ = header[0];
+        let id = u64::from_le_bytes(header[1..9].try_into().unwrap());
+        let length = usize::from_le_bytes(header[9..17].try_into().unwrap());
+
+        let mut payload = Vec::new();
+        payload.resize(length, 0u8);
+        if let Err(e) = reader.read(&mut payload) {
+            if e.kind() == ErrorKind::UnexpectedEof { return Ok(None); }
+            else { return Err(e); }
+        }
+
+        Ok(Some(Self { typ, id, payload }))
+    }
+}
diff --git a/utils/src/read_ext.rs b/utils/src/read_ext.rs
new file mode 100644
index 0000000..7695ada
--- /dev/null
+++ b/utils/src/read_ext.rs
@@ -0,0 +1,38 @@
+use std::convert::TryInto;
+
+pub trait ReadExt {
+    fn read_exact(&mut self, n: usize) -> Option<&[u8]>;
+
+    fn read_le_i32(&mut self) -> Option<i32> {
+        self.read_exact(4).map(|bytes| i32::from_le_bytes(bytes.try_into().unwrap()))
+    }
+
+    fn read_le_u32(&mut self) -> Option<u32> {
+        self.read_exact(4).map(|bytes| u32::from_le_bytes(bytes.try_into().unwrap()))
+    }
+
+    fn read_le_u64(&mut self) -> Option<u64> {
+        self.read_exact(8).map(|bytes| u64::from_le_bytes(bytes.try_into().unwrap()))
+    }
+
+    fn read_pascal_blob(&mut self) -> Option<&[u8]> {
+        let len = self.read_le_u64()?;
+        self.read_exact(len as usize)
+    }
+
+    fn read_pascal_string(&mut self) -> Option<Result<String, std::string::FromUtf8Error>> {
+        self.read_pascal_blob().map(|b| String::from_utf8(b.to_vec()))
+    }
+}
+
+impl ReadExt for &[u8] {
+    fn read_exact(&mut self, n: usize) -> Option<&[u8]> {
+        if self.len() >= n {
+            let (res, newlist) = self.split_at(n);
+            *self = newlist;
+            Some(res)
+        } else {
+            None
+        }
+    }
+}
diff --git a/worker/Cargo.toml b/worker/Cargo.toml
new file mode 100644
index 0000000..f9888c4
--- /dev/null
+++ b/worker/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "dd-worker"
+version = "0.1.0"
+authors = ["Tom Smeding <tom.smeding@gmail.com>"]
+edition = "2018"
+
+[dependencies]
+libloading = "0.5"
+static_assertions = "1.1"
+net2 = "0.2"
+tempfile = "3.1"
+dd-utils = { path = "../utils" }
diff --git a/worker/src/compute_core.rs b/worker/src/compute_core.rs
new file mode 100644
index 0000000..aec2a9d
--- /dev/null
+++ b/worker/src/compute_core.rs
@@ -0,0 +1,80 @@
+use std::io;
+use std::path::Path;
+use std::ffi::c_void;
+use libloading::{Library, Symbol};
+use static_assertions::assert_eq_size;
+use dd_utils::error::*;
+
+pub const CORE_API_VERSION: i32 = 1;
+
+pub struct ComputeCore {
+    #[used]
+    library: Library,
+    // init: unsafe extern "C" fn(i32) -> i32,
+    run_job: unsafe extern "C" fn(u64, *mut c_void, *mut u64, *mut *mut c_void) -> i32,
+    free_outdata: unsafe extern "C" fn(u64, *mut c_void),
+}
+
+impl ComputeCore {
+    pub fn load<P: AsRef<Path>>(lib_path: P) -> io::Result<Self> {
+        let lib_path = lib_path.as_ref();
+        let lib_path = lib_path.canonicalize().map_err(|e| {
+            format!("Library '{}' does not exist", lib_path.display()).perror(e)
+        })?;
+
+        let library = libloading::Library::new(&lib_path).map_err(|e| {
+            format!("Cannot load library at '{}'", lib_path.display()).perror(e)
+        })?;
+
+        macro_rules! load_symbol {
+            ($name:expr, $symname:expr, $typ:ty) => {{
+                let sym: io::Result<Symbol<$typ>> = library.get($symname).map_err(|e| {
+                    format!("Failed to load symbol '{}' from library '{}'", $name, lib_path.display()).perror(e)
+                });
+                sym.map(|s| std::mem::transmute::<*mut c_void, $typ>(s.into_raw().into_raw()))
+            }}
+        }
+
+        let init =         unsafe { load_symbol!("worker_init", b"worker_init\0", unsafe extern "C" fn(i32) -> i32)? };
+        let run_job =      unsafe { load_symbol!("worker_run_job",b"worker_run_job\0", unsafe extern "C" fn(u64, *mut c_void, *mut u64, *mut *mut c_void) -> i32)? };
+        let free_outdata = unsafe { load_symbol!("worker_free_outdata", b"worker_free_outdata\0", unsafe extern "C" fn(u64, *mut c_void))? };
+
+        let ret = unsafe {
+            init(CORE_API_VERSION)
+        };
+        if ret != 0 {
+            return Err(format!("Library refused initialisation at version {}: '{}'", CORE_API_VERSION, lib_path.display()).ioerr());
+        }
+
+        Ok(ComputeCore { library, /*init,*/ run_job, free_outdata })
+    }
+
+    /// Will block on this thread, so if you don't want to block, spawn a new thread.
+    /// This does not syntactically need mutability, but since one can only run one job at a time
+    /// on a core, semantic mutability seems warranted.
+    pub fn run_job(&mut self, input_data: &mut [u8]) -> (i32, Vec<u8>) {
+        let mut outsize = 0u64;
+        let mut outdataptr: *mut c_void = std::ptr::null_mut();
+
+        assert_eq_size!(u64, usize);
+
+        let ret = unsafe {
+            (self.run_job)(input_data.len() as u64, input_data.as_mut_ptr() as *mut c_void, &mut outsize, &mut outdataptr)
+        };
+
+        let mut result = (ret, Vec::new());
+
+        if outsize != 0 && outdataptr != std::ptr::null_mut() {
+            result.1.resize(outsize as usize, 0u8);
+            unsafe {
+                std::ptr::copy(outdataptr as *const u8, result.1.as_mut_ptr(), outsize as usize);
+            }
+        }
+
+        unsafe {
+            (self.free_outdata)(outsize, outdataptr);
+        }
+
+        result
+    }
+}
diff --git a/worker/src/connection.rs b/worker/src/connection.rs
new file mode 100644
index 0000000..1222c92
--- /dev/null
+++ b/worker/src/connection.rs
@@ -0,0 +1,119 @@
+use std::io::{self, BufReader, Write};
+use std::net::TcpStream;
+use net2::TcpStreamExt;
+use dd_utils::read_ext::ReadExt;
+use dd_utils::error::*;
+use dd_utils::protocol::*;
+
+fn send_vectored<W: Write, V: AsRef<[u8]>>(
+    writer: &mut W,
+    typ: u8,
+    id: u64,
+    payload: &[V]
+) -> io::Result<()> {
+    let mut header = [0u8; 17];
+    header[0] = typ;
+    header[1..9].copy_from_slice(&id.to_le_bytes());
+    let sumlen: usize = payload.iter().map(|v| v.as_ref().len()).sum();
+    header[9..17].copy_from_slice(&sumlen.to_le_bytes());
+    writer.write_all(&header)?;
+    for part in payload {
+        writer.write_all(part.as_ref())?;
+    }
+    Ok(())
+}
+
+pub struct Message {
+    pub id: u64,
+    pub body: MessageBody,
+}
+
+fn interpret_message(raw: RawMessage) -> io::Result<Message> {
+    let mut reader: &[u8] = &raw.payload;
+
+    macro_rules! too_short { () => { "Message payload too short!".ioerr() } }
+
+    match raw.typ {
+        1 => {
+            let version = reader.read_le_u32().ok_or(too_short!())?;
+            Ok(Message { id: raw.id, body: MessageBody::Version(version) })
+        }
+
+        2 => {
+            let name = reader.read_pascal_string()
+                            .map(|r| r.iores())
+                            .ok_or(too_short!())??;
+            let libfile = reader.read_pascal_blob()
+                            .map(|b| b.to_vec())
+                            .ok_or(too_short!())?;
+            Ok(Message { id: raw.id, body: MessageBody::NewCore(name, libfile) })
+        }
+
+        3 => {
+            let jobid = reader.read_le_u64().ok_or(too_short!())?;
+            let jobdata = reader.read_pascal_blob().map(|b| b.to_vec()).ok_or(too_short!())?;
+            Ok(Message { id: raw.id, body: MessageBody::Job(jobid, jobdata) })
+        }
+
+        _ => {
+            Err(format!("Unknown message type {}", raw.typ).ioerr())
+        }
+    }
+}
+
+pub struct Connection {
+    reader: BufReader<TcpStream>,
+}
+
+impl Connection {
+    pub fn new(address: &str) -> io::Result<Self> {
+        let socket = TcpStream::connect(address)?;
+
+        socket.set_keepalive_ms(Some(60000))?;
+
+        Ok(Self {
+            reader: BufReader::new(socket),
+        })
+    }
+
+    pub fn close(self) {}
+
+    pub fn receive(&mut self) -> io::Result<Option<Message>> {
+        RawMessage::receive(&mut self.reader)
+            .and_then(|opt|
+                opt.map(|rawmsg| interpret_message(rawmsg)).transpose()
+            )
+    }
+
+    pub fn reply(&mut self, msgid: u64, rmsg: Result<Reply, String>) -> io::Result<()> {
+        let socket = self.reader.get_mut();
+        let mut payload: Vec<Vec<u8>> = Vec::new();
+
+        let response_type;
+
+        match rmsg {
+            Ok(msg) => {
+                response_type = 1;
+                match msg {
+                    Reply::Version(ok) => {
+                        payload.push(vec![if ok { 1u8 } else { 0u8 }]);
+                    }
+
+                    Reply::NewCore => {}
+
+                    Reply::Job(jobid, output) => {
+                        payload.push(jobid.to_le_bytes().to_vec());
+                        payload.push(output);
+                    }
+                }
+            }
+
+            Err(err) => {
+                response_type = 0xff;
+                payload.push(err.into_bytes());
+            }
+        }
+
+        send_vectored(socket, response_type, msgid, &payload)
+    }
+}
diff --git a/worker/src/main.rs b/worker/src/main.rs
new file mode 100644
index 0000000..0300278
--- /dev/null
+++ b/worker/src/main.rs
@@ -0,0 +1,120 @@
+use std::env;
+use std::fs::File;
+use std::io::{self, Write};
+use std::process;
+use tempfile;
+use dd_utils::protocol::*;
+use crate::connection::Connection;
+use crate::compute_core::ComputeCore;
+
+mod compute_core;
+mod connection;
+
+#[repr(C)]
+struct mandel_input {
+	ltx: f64,
+    lty: f64,
+	rbx: f64,
+    rby: f64,
+	width: usize,
+    height: usize,
+	maxiter: usize,
+}
+
+fn aligned_buffer(num_bytes: usize, align_bits: usize, backend: &mut Vec<u8>) -> &mut [u8] {
+    assert!(align_bits > 0);
+
+    backend.resize(num_bytes + (1 << align_bits) - 1, 0u8);
+    let begin_ptr = backend.as_ptr() as usize;
+    let aligned_ptr = ((begin_ptr - 1) & !((1 << align_bits) - 1)) + (1 << align_bits);
+    let offset = aligned_ptr - begin_ptr;
+    &mut backend[offset .. offset + num_bytes]
+}
+
+fn main() -> io::Result<()> {
+    let args = env::args().collect::<Vec<_>>();
+    if args.len() != 2 {
+        eprintln!("Usage: {} <controller ip:port>", args[0]);
+        process::exit(1);
+    }
+
+    let controller_addr = &args[1];
+
+    let tempdir = tempfile::tempdir()?;
+
+    let mut conn = Connection::new(controller_addr)?;
+
+    let mut ccore: Option<ComputeCore> = None;
+
+    loop {
+        let opt_msg = conn.receive()?;
+        let msg = match opt_msg { Some(msg) => msg, None => break };
+
+        match msg.body {
+            MessageBody::Version(version) => {
+                if version == 1 {
+                    conn.reply(msg.id, Ok(Reply::Version(true)))?;
+                } else {
+                    conn.reply(msg.id, Ok(Reply::Version(false)))?;
+                    conn.close();
+                    break;
+                }
+            }
+
+            MessageBody::NewCore(_name, libfile) => {
+                let path = tempdir.path().join("core.so");
+
+                let res =
+                    File::open(&path)
+                        .and_then(|mut f| { f.write_all(&libfile)?; Ok(f) })
+                        .and_then(|f| {
+                            drop(f);
+                            ComputeCore::load(&path)
+                        });
+
+                match res {
+                    Ok(new_ccore) => {
+                        ccore = Some(new_ccore);
+                        conn.reply(msg.id, Ok(Reply::NewCore))?;
+                    }
+                    Err(err) => {
+                        conn.reply(msg.id, Err(format!("Could not load core: {}", err)))?;
+                    }
+                }
+            }
+
+            MessageBody::Job(_jobid, mut input) => {
+                if let Some(ccore) = &mut ccore {
+                    let (ret, output) = ccore.run_job(&mut input);
+                    conn.reply(msg.id, Ok(Reply::Job(ret, output)))?;
+                } else {
+                    conn.reply(msg.id, Err("No core loaded".to_string()))?;
+                }
+            }
+        }
+    }
+
+    // let mut core = compute_core::ComputeCore::load(&lib_fname)?;
+
+    // let mut input = b"kaas\0".to_vec();
+    // println!("Input: {:?} = {}", input, String::from_utf8_lossy(&input));
+    // let (ret, output) = core.run_job(&mut input);
+    // println!("Exit code: {}", ret);
+    // println!("Output: {:?} = {}", output, String::from_utf8_lossy(&output));
+
+    // let input = mandel_input {
+    //     ltx: -1.5, lty: 1.0,
+    //     rbx: 1.0, rby: 1.0,
+    //     width: 2000, height: 1600,
+    //     maxiter: 1024
+    // };
+    // let mut input_bytes_backend = Vec::new();
+    // let input_bytes = aligned_buffer(std::mem::size_of::<mandel_input>(), 3, &mut input_bytes_backend);
+    // unsafe {
+    //     std::ptr::copy(&input as *const mandel_input as *const u8, input_bytes.as_mut_ptr(), std::mem::size_of::<mandel_input>());
+    // }
+    // let (ret, output) = core.run_job(input_bytes);
+    // println!("ret = {}", ret);
+
+    Ok(())
+}