Concurrent hydra-evaluator
This rewrites the top-level loop of hydra-evaluator in C++. The Perl stuff is moved into hydra-eval-jobset. (Rewriting the entire evaluator would be nice but is a bit too much work.) The new version has some advantages: * It can run multiple jobset evaluations in parallel. * It uses PostgreSQL notifications so it doesn't have to poll the database. So if a jobset is triggered via the web interface or from a GitHub / Bitbucket webhook, evaluation of the jobset will start almost instantaneously (assuming the evaluator is not at its concurrency limit). * It imposes a timeout on evaluations. So if e.g. hydra-eval-jobset hangs connecting to a Mercurial server, it will eventually be killed.
This commit is contained in:
Eelco Dolstra
5
src/hydra-evaluator/Makefile.am
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src/hydra-evaluator/Makefile.am
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bin_PROGRAMS = hydra-evaluator
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hydra_evaluator_SOURCES = hydra-evaluator.cc
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hydra_evaluator_LDADD = $(NIX_LIBS) -lpqxx
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hydra_evaluator_CXXFLAGS = $(NIX_CFLAGS) -Wall -I ../libhydra
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275
src/hydra-evaluator/hydra-evaluator.cc
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src/hydra-evaluator/hydra-evaluator.cc
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#include "shared.hh"
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#include "db.hh"
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#include "pool.hh"
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#include <algorithm>
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#include <thread>
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#include <cstring>
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#include <sys/types.h>
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#include <sys/wait.h>
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using namespace nix;
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struct Evaluator
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{
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nix::Pool<Connection> dbPool;
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typedef std::pair<std::string, std::string> JobsetName;
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struct Jobset
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{
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JobsetName name;
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time_t lastCheckedTime, triggerTime;
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int checkInterval;
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Pid pid;
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};
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typedef std::map<JobsetName, Jobset> Jobsets;
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int evalTimeout = 3600;
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size_t maxEvals = 4;
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struct State
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{
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size_t runningEvals = 0;
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Jobsets jobsets;
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};
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Sync<State> state_;
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std::condition_variable childStarted;
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std::condition_variable maybeDoWork;
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const time_t notTriggered = std::numeric_limits<time_t>::max();
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void readJobsets()
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{
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auto conn(dbPool.get());
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pqxx::work txn(*conn);
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auto res = txn.parameterized
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("select project, j.name, lastCheckedTime, triggerTime, checkInterval from Jobsets j join Projects p on j.project = p.name "
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"where j.enabled != 0 and p.enabled != 0").exec();
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auto state(state_.lock());
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std::set<JobsetName> seen;
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for (auto const & row : res) {
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auto name = JobsetName{row["project"].as<std::string>(), row["name"].as<std::string>()};
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auto res = state->jobsets.try_emplace(name, Jobset{name});
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auto & jobset = res.first->second;
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jobset.lastCheckedTime = row["lastCheckedTime"].as<time_t>(0);
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jobset.triggerTime = row["triggerTime"].as<time_t>(notTriggered);
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jobset.checkInterval = row["checkInterval"].as<time_t>();
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seen.insert(name);
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}
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for (auto i = state->jobsets.begin(); i != state->jobsets.end(); )
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if (seen.count(i->first))
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++i;
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else {
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printInfo("forgetting jobset ‘%s:%s’", i->first.first, i->first.second);
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i = state->jobsets.erase(i);
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}
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}
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void startEval(State & state, Jobset & jobset)
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{
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printInfo("starting evaluation of jobset ‘%s:%s’", jobset.name.first, jobset.name.second);
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assert(jobset.pid == -1);
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jobset.pid = startProcess([&]() {
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Strings args = { "timeout", "-s", "KILL", std::to_string(evalTimeout), "hydra-eval-jobset", jobset.name.first, jobset.name.second };
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execvp(args.front().c_str(), stringsToCharPtrs(args).data());
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throw SysError(format("executing ‘%1%’") % args.front());
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});
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state.runningEvals++;
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childStarted.notify_one();
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time_t now = time(0);
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{
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auto conn(dbPool.get());
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pqxx::work txn(*conn);
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txn.parameterized
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("update Jobsets set lastCheckedTime = $1, triggerTime = null where project = $2 and name = $3")
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(now)
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(jobset.name.first)
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(jobset.name.second)
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.exec();
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txn.commit();
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jobset.lastCheckedTime = now;
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jobset.triggerTime = notTriggered;
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}
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}
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void startEvals(State & state)
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{
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std::vector<Jobsets::iterator> sorted;
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time_t now = time(0);
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/* Filter out jobsets that have been evaluated recently and have
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not been triggered. */
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for (auto i = state.jobsets.begin(); i != state.jobsets.end(); ++i)
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if (i->second.pid == -1 &&
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(i->second.triggerTime != std::numeric_limits<time_t>::max() ||
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(i->second.checkInterval > 0 && i->second.lastCheckedTime + i->second.checkInterval <= now)))
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sorted.push_back(i);
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/* Put jobsets in order of ascending trigger time, last checked
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time, and name. */
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std::sort(sorted.begin(), sorted.end(),
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[](const Jobsets::iterator & a, const Jobsets::iterator & b) {
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return
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a->second.triggerTime != b->second.triggerTime
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? a->second.triggerTime < b->second.triggerTime
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: a->second.lastCheckedTime != b->second.lastCheckedTime
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? a->second.lastCheckedTime < b->second.lastCheckedTime
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: a->first < b->first;
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});
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/* Start jobset evaluations up to the concurrency limit.*/
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for (auto & i : sorted) {
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if (state.runningEvals >= maxEvals) break;
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startEval(state, i->second);
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}
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}
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void loop()
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{
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auto state(state_.lock());
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while (true) {
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time_t now = time(0);
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std::chrono::seconds sleepTime = std::chrono::seconds::max();
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if (state->runningEvals < maxEvals) {
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for (auto & i : state->jobsets)
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if (i.second.pid == -1 &&
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i.second.checkInterval > 0)
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sleepTime = std::min(sleepTime, std::chrono::seconds(
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std::max((time_t) 1, i.second.lastCheckedTime - now + i.second.checkInterval)));
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}
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debug("waiting for %d s", sleepTime.count());
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if (sleepTime == std::chrono::seconds::max())
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state.wait(maybeDoWork);
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else
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state.wait_for(maybeDoWork, sleepTime);
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startEvals(*state);
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}
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}
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/* A thread that listens to PostgreSQL notifications about jobset
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changes, updates the jobsets map, and signals the main thread
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to start evaluations. */
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void databaseMonitor()
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{
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while (true) {
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try {
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auto conn(dbPool.get());
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receiver jobsetsAdded(*conn, "jobsets_added");
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receiver jobsetsDeleted(*conn, "jobsets_deleted");
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receiver jobsetsChanged(*conn, "jobset_scheduling_changed");
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while (true) {
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/* Note: we read/notify before
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await_notification() to ensure we don't miss a
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state change. */
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readJobsets();
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maybeDoWork.notify_one();
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conn->await_notification();
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printInfo("received jobset event");
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}
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} catch (std::exception & e) {
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printError("exception in database monitor thread: %s", e.what());
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sleep(30);
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}
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}
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}
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/* A thread that reaps child processes.*/
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void reaper()
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{
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while (true) {
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{
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auto state(state_.lock());
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while (!state->runningEvals)
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state.wait(childStarted);
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}
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int status;
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pid_t pid = waitpid(-1, &status, 0);
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if (pid == -1) {
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if (errno == EINTR) continue;
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throw SysError("waiting for children");
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}
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{
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auto state(state_.lock());
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assert(state->runningEvals);
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state->runningEvals--;
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for (auto & jobset : state->jobsets)
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if (jobset.second.pid == pid) {
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printInfo("evaluation of jobset ‘%s:%s’ finished with status %d",
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jobset.first.first, jobset.first.second, status);
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jobset.second.pid.release();
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maybeDoWork.notify_one();
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break;
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}
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}
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}
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}
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void run()
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{
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std::thread reaperThread([&]() { reaper(); });
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std::thread monitorThread([&]() { databaseMonitor(); });
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while (true) {
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try {
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loop();
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} catch (std::exception & e) {
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printError("exception in main loop: %s", e.what());
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sleep(30);
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}
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}
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}
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};
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int main(int argc, char * * argv)
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{
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return handleExceptions(argv[0], [&]() {
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initNix();
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signal(SIGINT, SIG_DFL);
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signal(SIGTERM, SIG_DFL);
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signal(SIGHUP, SIG_DFL);
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parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
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return false;
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});
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Evaluator().run();
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});
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}
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