#pragma once #include "sync.hh" #include "util.hh" #include <queue> #include <functional> #include <thread> #include <map> namespace nix { MakeError(ThreadPoolShutDown, Error) /* A simple thread pool that executes a queue of work items (lambdas). */ class ThreadPool { public: ThreadPool(size_t maxThreads = 0); ~ThreadPool(); // FIXME: use std::packaged_task? typedef std::function<void()> work_t; /* Enqueue a function to be executed by the thread pool. */ void enqueue(const work_t & t); /* Execute work items until the queue is empty. Note that work items are allowed to add new items to the queue; this is handled correctly. Queue processing stops prematurely if any work item throws an exception. This exception is propagated to the calling thread. If multiple work items throw an exception concurrently, only one item is propagated; the others are printed on stderr and otherwise ignored. */ void process(); private: size_t maxThreads; struct State { std::queue<work_t> left; size_t pending = 0; std::exception_ptr exception; std::vector<std::thread> workers; bool quit = false; }; Sync<State> state_; std::condition_variable work, done; void workerEntry(); }; /* Process in parallel a set of items of type T that have a partial ordering between them. Thus, any item is only processed after all its dependencies have been processed. */ template<typename T> void processGraph( ThreadPool & pool, const std::set<T> & nodes, std::function<std::set<T>(const T &)> getEdges, std::function<void(const T &)> processNode) { struct Graph { std::set<T> left; std::map<T, std::set<T>> refs, rrefs; std::function<void(T)> wrap; }; ref<Sync<Graph>> graph_ = make_ref<Sync<Graph>>(); auto wrapWork = [&pool, graph_, processNode](const T & node) { processNode(node); /* Enqueue work for all nodes that were waiting on this one. */ { auto graph(graph_->lock()); graph->left.erase(node); for (auto & rref : graph->rrefs[node]) { auto & refs(graph->refs[rref]); auto i = refs.find(node); assert(i != refs.end()); refs.erase(i); if (refs.empty()) pool.enqueue(std::bind(graph->wrap, rref)); } } }; { auto graph(graph_->lock()); graph->left = nodes; graph->wrap = wrapWork; } /* Build the dependency graph; enqueue all nodes with no dependencies. */ for (auto & node : nodes) { auto refs = getEdges(node); { auto graph(graph_->lock()); for (auto & ref : refs) if (ref != node && graph->left.count(ref)) { graph->refs[node].insert(ref); graph->rrefs[ref].insert(node); } if (graph->refs[node].empty()) pool.enqueue(std::bind(graph->wrap, node)); } } } }