From 39b2a399ad94f061eea0e0fc639cf1466587959e Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Fri, 10 May 2024 13:03:05 -0400
Subject: [PATCH] Start building the scheduler for Windows

Building derivations is a lot harder, but the downloading goals is
portable enough.

The "common channel" code is due to Volth. I wonder if there is a way we
can factor it out into separate functions / files to avoid some
within-function CPP.

Co-authored-by: volth <volth@volth.com>
---
 maintainers/flake-module.nix                  |  22 ++--
 .../build/drv-output-substitution-goal.cc     |  14 ++-
 .../build/drv-output-substitution-goal.hh     |  15 ++-
 src/libstore/{unix => }/build/entry-points.cc |  14 ++-
 src/libstore/{unix => }/build/goal.cc         |   0
 src/libstore/{unix => }/build/goal.hh         |   4 +-
 .../{unix => }/build/substitution-goal.cc     |  16 ++-
 .../{unix => }/build/substitution-goal.hh     |  13 ++-
 src/libstore/{unix => }/build/worker.cc       | 110 ++++++++++++++++--
 src/libstore/{unix => }/build/worker.hh       |  33 +++++-
 src/libstore/local.mk                         |   4 +-
 src/libstore/unix/build/derivation-goal.cc    |   4 +-
 src/libstore/unix/build/derivation-goal.hh    |   6 +-
 src/libstore/unix/{lock.cc => user-lock.cc}   |   2 +-
 src/libstore/unix/{lock.hh => user-lock.hh}   |   0
 src/libstore/windows/build.cc                 |  37 ------
 src/libstore/windows/pathlocks.cc             |   2 +
 src/libutil/error.hh                          |  10 +-
 src/libutil/serialise.cc                      |   2 +-
 src/libutil/windows/file-descriptor.cc        |   2 +
 src/libutil/windows/users.cc                  |   2 +
 src/libutil/windows/windows-async-pipe.cc     |  43 +++++++
 src/libutil/windows/windows-async-pipe.hh     |  20 ++++
 src/libutil/windows/windows-error.cc          |   2 +-
 src/libutil/windows/windows-error.hh          |   2 +-
 25 files changed, 285 insertions(+), 94 deletions(-)
 rename src/libstore/{unix => }/build/drv-output-substitution-goal.cc (93%)
 rename src/libstore/{unix => }/build/drv-output-substitution-goal.hh (90%)
 rename src/libstore/{unix => }/build/entry-points.cc (90%)
 rename src/libstore/{unix => }/build/goal.cc (100%)
 rename src/libstore/{unix => }/build/goal.hh (97%)
 rename src/libstore/{unix => }/build/substitution-goal.cc (96%)
 rename src/libstore/{unix => }/build/substitution-goal.hh (91%)
 rename src/libstore/{unix => }/build/worker.cc (81%)
 rename src/libstore/{unix => }/build/worker.hh (92%)
 rename src/libstore/unix/{lock.cc => user-lock.cc} (99%)
 rename src/libstore/unix/{lock.hh => user-lock.hh} (100%)
 delete mode 100644 src/libstore/windows/build.cc
 create mode 100644 src/libutil/windows/windows-async-pipe.cc
 create mode 100644 src/libutil/windows/windows-async-pipe.hh

diff --git a/maintainers/flake-module.nix b/maintainers/flake-module.nix
index 351a01fcb..e541aeda8 100644
--- a/maintainers/flake-module.nix
+++ b/maintainers/flake-module.nix
@@ -227,18 +227,18 @@
         ''^src/libstore/store-dir-config\.hh$''
         ''^src/libstore/unix/build/derivation-goal\.cc$''
         ''^src/libstore/unix/build/derivation-goal\.hh$''
-        ''^src/libstore/unix/build/drv-output-substitution-goal\.cc$''
-        ''^src/libstore/unix/build/drv-output-substitution-goal\.hh$''
-        ''^src/libstore/unix/build/entry-points\.cc$''
-        ''^src/libstore/unix/build/goal\.cc$''
-        ''^src/libstore/unix/build/goal\.hh$''
+        ''^src/libstore/build/drv-output-substitution-goal\.cc$''
+        ''^src/libstore/build/drv-output-substitution-goal\.hh$''
+        ''^src/libstore/build/entry-points\.cc$''
+        ''^src/libstore/build/goal\.cc$''
+        ''^src/libstore/build/goal\.hh$''
         ''^src/libstore/unix/build/hook-instance\.cc$''
         ''^src/libstore/unix/build/local-derivation-goal\.cc$''
         ''^src/libstore/unix/build/local-derivation-goal\.hh$''
-        ''^src/libstore/unix/build/substitution-goal\.cc$''
-        ''^src/libstore/unix/build/substitution-goal\.hh$''
-        ''^src/libstore/unix/build/worker\.cc$''
-        ''^src/libstore/unix/build/worker\.hh$''
+        ''^src/libstore/build/substitution-goal\.cc$''
+        ''^src/libstore/build/substitution-goal\.hh$''
+        ''^src/libstore/build/worker\.cc$''
+        ''^src/libstore/build/worker\.hh$''
         ''^src/libstore/unix/builtins/fetchurl\.cc$''
         ''^src/libstore/unix/builtins/unpack-channel\.cc$''
         ''^src/libstore/gc\.cc$''
@@ -246,8 +246,8 @@
         ''^src/libstore/unix/local-overlay-store\.hh$''
         ''^src/libstore/local-store\.cc$''
         ''^src/libstore/local-store\.hh$''
-        ''^src/libstore/unix/lock\.cc$''
-        ''^src/libstore/unix/lock\.hh$''
+        ''^src/libstore/unix/user-lock\.cc$''
+        ''^src/libstore/unix/user-lock\.hh$''
         ''^src/libstore/optimise-store\.cc$''
         ''^src/libstore/unix/pathlocks\.cc$''
         ''^src/libstore/posix-fs-canonicalise\.cc$''
diff --git a/src/libstore/unix/build/drv-output-substitution-goal.cc b/src/libstore/build/drv-output-substitution-goal.cc
similarity index 93%
rename from src/libstore/unix/build/drv-output-substitution-goal.cc
rename to src/libstore/build/drv-output-substitution-goal.cc
index b30957c84..13a07e4ea 100644
--- a/src/libstore/unix/build/drv-output-substitution-goal.cc
+++ b/src/libstore/build/drv-output-substitution-goal.cc
@@ -66,7 +66,11 @@ void DrvOutputSubstitutionGoal::tryNext()
        some other error occurs), so it must not touch `this`. So put
        the shared state in a separate refcounted object. */
     downloadState = std::make_shared<DownloadState>();
+#ifndef _WIN32
     downloadState->outPipe.create();
+#else
+    downloadState->outPipe.createAsyncPipe(worker.ioport.get());
+#endif
 
     sub->queryRealisation(
         id,
@@ -79,7 +83,13 @@ void DrvOutputSubstitutionGoal::tryNext()
             }
         } });
 
-    worker.childStarted(shared_from_this(), {downloadState->outPipe.readSide.get()}, true, false);
+    worker.childStarted(shared_from_this(), {
+#ifndef _WIN32
+        downloadState->outPipe.readSide.get()
+#else
+        &downloadState->outPipe
+#endif
+    }, true, false);
 
     state = &DrvOutputSubstitutionGoal::realisationFetched;
 }
@@ -158,7 +168,7 @@ void DrvOutputSubstitutionGoal::work()
     (this->*state)();
 }
 
-void DrvOutputSubstitutionGoal::handleEOF(int fd)
+void DrvOutputSubstitutionGoal::handleEOF(Descriptor fd)
 {
     if (fd == downloadState->outPipe.readSide.get()) worker.wakeUp(shared_from_this());
 }
diff --git a/src/libstore/unix/build/drv-output-substitution-goal.hh b/src/libstore/build/drv-output-substitution-goal.hh
similarity index 90%
rename from src/libstore/unix/build/drv-output-substitution-goal.hh
rename to src/libstore/build/drv-output-substitution-goal.hh
index da2426e5e..4f06a9e9e 100644
--- a/src/libstore/unix/build/drv-output-substitution-goal.hh
+++ b/src/libstore/build/drv-output-substitution-goal.hh
@@ -1,11 +1,16 @@
 #pragma once
 ///@file
 
+#include <thread>
+#include <future>
+
 #include "store-api.hh"
 #include "goal.hh"
 #include "realisation.hh"
-#include <thread>
-#include <future>
+
+#ifdef _WIN32
+#  include "windows-async-pipe.hh"
+#endif
 
 namespace nix {
 
@@ -43,7 +48,11 @@ class DrvOutputSubstitutionGoal : public Goal {
 
     struct DownloadState
     {
+#ifndef _WIN32
         Pipe outPipe;
+#else
+        windows::AsyncPipe outPipe;
+#endif
         std::promise<std::shared_ptr<const Realisation>> promise;
     };
 
@@ -71,7 +80,7 @@ public:
     std::string key() override;
 
     void work() override;
-    void handleEOF(int fd) override;
+    void handleEOF(Descriptor fd) override;
 
     JobCategory jobCategory() const override {
         return JobCategory::Substitution;
diff --git a/src/libstore/unix/build/entry-points.cc b/src/libstore/build/entry-points.cc
similarity index 90%
rename from src/libstore/unix/build/entry-points.cc
rename to src/libstore/build/entry-points.cc
index d4bead28e..784f618c1 100644
--- a/src/libstore/unix/build/entry-points.cc
+++ b/src/libstore/build/entry-points.cc
@@ -1,6 +1,8 @@
 #include "worker.hh"
 #include "substitution-goal.hh"
-#include "derivation-goal.hh"
+#ifndef _WIN32 // TODO Enable building on Windows
+#  include "derivation-goal.hh"
+#endif
 #include "local-store.hh"
 
 namespace nix {
@@ -25,9 +27,12 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
                 ex = std::move(i->ex);
         }
         if (i->exitCode != Goal::ecSuccess) {
+#ifndef _WIN32 // TODO Enable building on Windows
             if (auto i2 = dynamic_cast<DerivationGoal *>(i.get()))
                 failed.insert(printStorePath(i2->drvPath));
-            else if (auto i2 = dynamic_cast<PathSubstitutionGoal *>(i.get()))
+            else
+#endif
+            if (auto i2 = dynamic_cast<PathSubstitutionGoal *>(i.get()))
                 failed.insert(printStorePath(i2->storePath));
         }
     }
@@ -74,7 +79,12 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
     BuildMode buildMode)
 {
     Worker worker(*this, *this);
+#ifndef _WIN32 // TODO Enable building on Windows
     auto goal = worker.makeBasicDerivationGoal(drvPath, drv, OutputsSpec::All {}, buildMode);
+#else
+    std::shared_ptr<Goal> goal;
+    throw UnimplementedError("Building derivations not yet implemented on windows.");
+#endif
 
     try {
         worker.run(Goals{goal});
diff --git a/src/libstore/unix/build/goal.cc b/src/libstore/build/goal.cc
similarity index 100%
rename from src/libstore/unix/build/goal.cc
rename to src/libstore/build/goal.cc
diff --git a/src/libstore/unix/build/goal.hh b/src/libstore/build/goal.hh
similarity index 97%
rename from src/libstore/unix/build/goal.hh
rename to src/libstore/build/goal.hh
index 9af083230..0d9b828e1 100644
--- a/src/libstore/unix/build/goal.hh
+++ b/src/libstore/build/goal.hh
@@ -138,12 +138,12 @@ public:
 
     virtual void waiteeDone(GoalPtr waitee, ExitCode result);
 
-    virtual void handleChildOutput(int fd, std::string_view data)
+    virtual void handleChildOutput(Descriptor fd, std::string_view data)
     {
         abort();
     }
 
-    virtual void handleEOF(int fd)
+    virtual void handleEOF(Descriptor fd)
     {
         abort();
     }
diff --git a/src/libstore/unix/build/substitution-goal.cc b/src/libstore/build/substitution-goal.cc
similarity index 96%
rename from src/libstore/unix/build/substitution-goal.cc
rename to src/libstore/build/substitution-goal.cc
index c7e8e2825..0be3d1e8d 100644
--- a/src/libstore/unix/build/substitution-goal.cc
+++ b/src/libstore/build/substitution-goal.cc
@@ -212,7 +212,11 @@ void PathSubstitutionGoal::tryToRun()
     maintainRunningSubstitutions = std::make_unique<MaintainCount<uint64_t>>(worker.runningSubstitutions);
     worker.updateProgress();
 
+#ifndef _WIN32
     outPipe.create();
+#else
+    outPipe.createAsyncPipe(worker.ioport.get());
+#endif
 
     promise = std::promise<void>();
 
@@ -235,7 +239,13 @@ void PathSubstitutionGoal::tryToRun()
         }
     });
 
-    worker.childStarted(shared_from_this(), {outPipe.readSide.get()}, true, false);
+    worker.childStarted(shared_from_this(), {
+#ifndef _WIN32
+        outPipe.readSide.get()
+#else
+        &outPipe
+#endif
+    }, true, false);
 
     state = &PathSubstitutionGoal::finished;
 }
@@ -294,12 +304,12 @@ void PathSubstitutionGoal::finished()
 }
 
 
-void PathSubstitutionGoal::handleChildOutput(int fd, std::string_view data)
+void PathSubstitutionGoal::handleChildOutput(Descriptor fd, std::string_view data)
 {
 }
 
 
-void PathSubstitutionGoal::handleEOF(int fd)
+void PathSubstitutionGoal::handleEOF(Descriptor fd)
 {
     if (fd == outPipe.readSide.get()) worker.wakeUp(shared_from_this());
 }
diff --git a/src/libstore/unix/build/substitution-goal.hh b/src/libstore/build/substitution-goal.hh
similarity index 91%
rename from src/libstore/unix/build/substitution-goal.hh
rename to src/libstore/build/substitution-goal.hh
index 1d389d328..58d309424 100644
--- a/src/libstore/unix/build/substitution-goal.hh
+++ b/src/libstore/build/substitution-goal.hh
@@ -1,10 +1,13 @@
 #pragma once
 ///@file
 
-#include "lock.hh"
 #include "store-api.hh"
 #include "goal.hh"
 
+#ifdef _WIN32
+#  include "windows-async-pipe.hh"
+#endif
+
 namespace nix {
 
 class Worker;
@@ -45,7 +48,11 @@ struct PathSubstitutionGoal : public Goal
     /**
      * Pipe for the substituter's standard output.
      */
+#ifndef _WIN32
     Pipe outPipe;
+#else
+    windows::AsyncPipe outPipe;
+#endif
 
     /**
      * The substituter thread.
@@ -111,8 +118,8 @@ public:
     /**
      * Callback used by the worker to write to the log.
      */
-    void handleChildOutput(int fd, std::string_view data) override;
-    void handleEOF(int fd) override;
+    void handleChildOutput(Descriptor fd, std::string_view data) override;
+    void handleEOF(Descriptor fd) override;
 
     /* Called by destructor, can't be overridden */
     void cleanup() override final;
diff --git a/src/libstore/unix/build/worker.cc b/src/libstore/build/worker.cc
similarity index 81%
rename from src/libstore/unix/build/worker.cc
rename to src/libstore/build/worker.cc
index 03fc280a4..ac6f693a2 100644
--- a/src/libstore/unix/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -1,12 +1,20 @@
+#include "local-store.hh"
 #include "machines.hh"
 #include "worker.hh"
 #include "substitution-goal.hh"
 #include "drv-output-substitution-goal.hh"
-#include "local-derivation-goal.hh"
-#include "hook-instance.hh"
+#ifndef _WIN32 // TODO Enable building on Windows
+#  include "local-derivation-goal.hh"
+#  include "hook-instance.hh"
+#endif
 #include "signals.hh"
 
-#include <poll.h>
+#ifndef _WIN32
+#  include <poll.h>
+#else
+#  include <ioapiset.h>
+#  include "windows-error.hh"
+#endif
 
 namespace nix {
 
@@ -41,6 +49,7 @@ Worker::~Worker()
     assert(expectedNarSize == 0);
 }
 
+#ifndef _WIN32 // TODO Enable building on Windows
 
 std::shared_ptr<DerivationGoal> Worker::makeDerivationGoalCommon(
     const StorePath & drvPath,
@@ -70,7 +79,6 @@ std::shared_ptr<DerivationGoal> Worker::makeDerivationGoal(const StorePath & drv
     });
 }
 
-
 std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(const StorePath & drvPath,
     const BasicDerivation & drv, const OutputsSpec & wantedOutputs, BuildMode buildMode)
 {
@@ -81,6 +89,8 @@ std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(const StorePath
     });
 }
 
+#endif
+
 
 std::shared_ptr<PathSubstitutionGoal> Worker::makePathSubstitutionGoal(const StorePath & path, RepairFlag repair, std::optional<ContentAddress> ca)
 {
@@ -112,10 +122,14 @@ GoalPtr Worker::makeGoal(const DerivedPath & req, BuildMode buildMode)
 {
     return std::visit(overloaded {
         [&](const DerivedPath::Built & bfd) -> GoalPtr {
+#ifndef _WIN32 // TODO Enable building on Windows
             if (auto bop = std::get_if<DerivedPath::Opaque>(&*bfd.drvPath))
                 return makeDerivationGoal(bop->path, bfd.outputs, buildMode);
             else
                 throw UnimplementedError("Building dynamic derivations in one shot is not yet implemented.");
+#else
+            throw UnimplementedError("Building derivations not yet implemented on Windows");
+#endif
         },
         [&](const DerivedPath::Opaque & bo) -> GoalPtr {
             return makePathSubstitutionGoal(bo.path, buildMode == bmRepair ? Repair : NoRepair);
@@ -141,9 +155,12 @@ static void removeGoal(std::shared_ptr<G> goal, std::map<K, std::weak_ptr<G>> &
 
 void Worker::removeGoal(GoalPtr goal)
 {
+#ifndef _WIN32 // TODO Enable building on Windows
     if (auto drvGoal = std::dynamic_pointer_cast<DerivationGoal>(goal))
         nix::removeGoal(drvGoal, derivationGoals);
-    else if (auto subGoal = std::dynamic_pointer_cast<PathSubstitutionGoal>(goal))
+    else
+#endif
+    if (auto subGoal = std::dynamic_pointer_cast<PathSubstitutionGoal>(goal))
         nix::removeGoal(subGoal, substitutionGoals);
     else if (auto subGoal = std::dynamic_pointer_cast<DrvOutputSubstitutionGoal>(goal))
         nix::removeGoal(subGoal, drvOutputSubstitutionGoals);
@@ -187,13 +204,13 @@ unsigned Worker::getNrSubstitutions()
 }
 
 
-void Worker::childStarted(GoalPtr goal, const std::set<int> & fds,
+void Worker::childStarted(GoalPtr goal, const std::set<Child::CommChannel> & channels,
     bool inBuildSlot, bool respectTimeouts)
 {
     Child child;
     child.goal = goal;
     child.goal2 = goal.get();
-    child.fds = fds;
+    child.channels = channels;
     child.timeStarted = child.lastOutput = steady_time_point::clock::now();
     child.inBuildSlot = inBuildSlot;
     child.respectTimeouts = respectTimeouts;
@@ -281,12 +298,15 @@ void Worker::run(const Goals & _topGoals)
 
     for (auto & i : _topGoals) {
         topGoals.insert(i);
+#ifndef _WIN32 // TODO Enable building on Windows
         if (auto goal = dynamic_cast<DerivationGoal *>(i.get())) {
             topPaths.push_back(DerivedPath::Built {
                 .drvPath = makeConstantStorePathRef(goal->drvPath),
                 .outputs = goal->wantedOutputs,
             });
-        } else if (auto goal = dynamic_cast<PathSubstitutionGoal *>(i.get())) {
+        } else
+#endif
+        if (auto goal = dynamic_cast<PathSubstitutionGoal *>(i.get())) {
             topPaths.push_back(DerivedPath::Opaque{goal->storePath});
         }
     }
@@ -408,13 +428,14 @@ void Worker::waitForInput()
     if (useTimeout)
         vomit("sleeping %d seconds", timeout);
 
+#ifndef _WIN32
     /* Use select() to wait for the input side of any logger pipe to
        become `available'.  Note that `available' (i.e., non-blocking)
        includes EOF. */
     std::vector<struct pollfd> pollStatus;
     std::map<int, size_t> fdToPollStatus;
     for (auto & i : children) {
-        for (auto & j : i.fds) {
+        for (auto & j : i.channels) {
             pollStatus.push_back((struct pollfd) { .fd = j, .events = POLLIN });
             fdToPollStatus[j] = pollStatus.size() - 1;
         }
@@ -425,6 +446,28 @@ void Worker::waitForInput()
         if (errno == EINTR) return;
         throw SysError("waiting for input");
     }
+#else
+    OVERLAPPED_ENTRY oentries[0x20] = {0};
+    ULONG removed;
+    bool gotEOF = false;
+
+    // we are on at least Windows Vista / Server 2008 and can get many (countof(oentries)) statuses in one API call
+    if (!GetQueuedCompletionStatusEx(
+        ioport.get(),
+        oentries,
+        sizeof(oentries) / sizeof(*oentries),
+        &removed,
+        useTimeout ? timeout * 1000 : INFINITE,
+        false))
+    {
+        windows::WinError winError("GetQueuedCompletionStatusEx");
+        if (winError.lastError != WAIT_TIMEOUT)
+            throw winError;
+        assert(removed == 0);
+    } else {
+        assert(0 < removed && removed <= sizeof(oentries)/sizeof(*oentries));
+    }
+#endif
 
     auto after = steady_time_point::clock::now();
 
@@ -439,20 +482,21 @@ void Worker::waitForInput()
         GoalPtr goal = j->goal.lock();
         assert(goal);
 
-        std::set<int> fds2(j->fds);
+#ifndef _WIN32
+        std::set<Descriptor> fds2(j->channels);
         std::vector<unsigned char> buffer(4096);
         for (auto & k : fds2) {
             const auto fdPollStatusId = get(fdToPollStatus, k);
             assert(fdPollStatusId);
             assert(*fdPollStatusId < pollStatus.size());
             if (pollStatus.at(*fdPollStatusId).revents) {
-                ssize_t rd = ::read(k, buffer.data(), buffer.size());
+                ssize_t rd = ::read(fromDescriptorReadOnly(k), buffer.data(), buffer.size());
                 // FIXME: is there a cleaner way to handle pt close
                 // than EIO? Is this even standard?
                 if (rd == 0 || (rd == -1 && errno == EIO)) {
                     debug("%1%: got EOF", goal->getName());
                     goal->handleEOF(k);
-                    j->fds.erase(k);
+                    j->channels.erase(k);
                 } else if (rd == -1) {
                     if (errno != EINTR)
                         throw SysError("%s: read failed", goal->getName());
@@ -465,6 +509,48 @@ void Worker::waitForInput()
                 }
             }
         }
+#else
+        decltype(j->channels)::iterator p = j->channels.begin();
+        while (p != j->channels.end()) {
+            decltype(p) nextp = p;
+            ++nextp;
+            for (ULONG i = 0; i < removed; i++) {
+                if (oentries[i].lpCompletionKey == ((ULONG_PTR)((*p)->readSide.get()) ^ 0x5555)) {
+                    printMsg(lvlVomit, "%s: read %s bytes", goal->getName(), oentries[i].dwNumberOfBytesTransferred);
+                    if (oentries[i].dwNumberOfBytesTransferred > 0) {
+                        std::string data {
+                            (char *) (*p)->buffer.data(),
+                            oentries[i].dwNumberOfBytesTransferred,
+                        };
+                        //std::cerr << "read  [" << data << "]" << std::endl;
+                        j->lastOutput = after;
+                        goal->handleChildOutput((*p)->readSide.get(), data);
+                    }
+
+                    if (gotEOF) {
+                        debug("%s: got EOF", goal->getName());
+                        goal->handleEOF((*p)->readSide.get());
+                        nextp = j->channels.erase(p); // no need to maintain `j->channels` ?
+                    } else {
+                        BOOL rc = ReadFile((*p)->readSide.get(), (*p)->buffer.data(), (*p)->buffer.size(), &(*p)->got, &(*p)->overlapped);
+                        if (rc) {
+                            // here is possible (but not obligatory) to call `goal->handleChildOutput` and repeat ReadFile immediately
+                        } else {
+                            windows::WinError winError("ReadFile(%s, ..)", (*p)->readSide.get());
+                            if (winError.lastError == ERROR_BROKEN_PIPE) {
+                                debug("%s: got EOF", goal->getName());
+                                goal->handleEOF((*p)->readSide.get());
+                                nextp = j->channels.erase(p); // no need to maintain `j->channels` ?
+                            } else if (winError.lastError != ERROR_IO_PENDING)
+                                throw winError;
+                        }
+                    }
+                    break;
+                }
+            }
+            p = nextp;
+        }
+#endif
 
         if (goal->exitCode == Goal::ecBusy &&
             0 != settings.maxSilentTime &&
diff --git a/src/libstore/unix/build/worker.hh b/src/libstore/build/worker.hh
similarity index 92%
rename from src/libstore/unix/build/worker.hh
rename to src/libstore/build/worker.hh
index ced013ddd..b57734b45 100644
--- a/src/libstore/unix/build/worker.hh
+++ b/src/libstore/build/worker.hh
@@ -2,18 +2,23 @@
 ///@file
 
 #include "types.hh"
-#include "lock.hh"
 #include "store-api.hh"
 #include "goal.hh"
 #include "realisation.hh"
 
+#ifdef _WIN32
+#  include "windows-async-pipe.hh"
+#endif
+
 #include <future>
 #include <thread>
 
 namespace nix {
 
 /* Forward definition. */
+#ifndef _WIN32 // TODO Enable building on Windows
 struct DerivationGoal;
+#endif
 struct PathSubstitutionGoal;
 class DrvOutputSubstitutionGoal;
 
@@ -36,14 +41,22 @@ typedef std::chrono::time_point<std::chrono::steady_clock> steady_time_point;
 
 /**
  * A mapping used to remember for each child process to what goal it
- * belongs, and file descriptors for receiving log data and output
+ * belongs, and comm channels for receiving log data and output
  * path creation commands.
  */
 struct Child
 {
+    using CommChannel =
+#ifndef _WIN32
+        Descriptor
+#else
+        windows::AsyncPipe *
+#endif
+        ;
+
     WeakGoalPtr goal;
     Goal * goal2; // ugly hackery
-    std::set<int> fds;
+    std::set<CommChannel> channels;
     bool respectTimeouts;
     bool inBuildSlot;
     /**
@@ -53,8 +66,10 @@ struct Child
     steady_time_point timeStarted;
 };
 
+#ifndef _WIN32 // TODO Enable building on Windows
 /* Forward definition. */
 struct HookInstance;
+#endif
 
 /**
  * The worker class.
@@ -101,7 +116,9 @@ private:
      * Maps used to prevent multiple instantiations of a goal for the
      * same derivation / path.
      */
+#ifndef _WIN32 // TODO Enable building on Windows
     std::map<StorePath, std::weak_ptr<DerivationGoal>> derivationGoals;
+#endif
     std::map<StorePath, std::weak_ptr<PathSubstitutionGoal>> substitutionGoals;
     std::map<DrvOutput, std::weak_ptr<DrvOutputSubstitutionGoal>> drvOutputSubstitutionGoals;
 
@@ -152,10 +169,16 @@ public:
      */
     bool checkMismatch;
 
+#ifdef _WIN32
+    AutoCloseFD ioport;
+#endif
+
     Store & store;
     Store & evalStore;
 
+#ifndef _WIN32 // TODO Enable building on Windows
     std::unique_ptr<HookInstance> hook;
+#endif
 
     uint64_t expectedBuilds = 0;
     uint64_t doneBuilds = 0;
@@ -184,6 +207,7 @@ public:
      * Make a goal (with caching).
      */
 
+#ifndef _WIN32 // TODO Enable building on Windows
     /**
      * @ref DerivationGoal "derivation goal"
      */
@@ -198,6 +222,7 @@ public:
     std::shared_ptr<DerivationGoal> makeBasicDerivationGoal(
         const StorePath & drvPath, const BasicDerivation & drv,
         const OutputsSpec & wantedOutputs, BuildMode buildMode = bmNormal);
+#endif
 
     /**
      * @ref SubstitutionGoal "substitution goal"
@@ -238,7 +263,7 @@ public:
      * Registers a running child process.  `inBuildSlot` means that
      * the process counts towards the jobs limit.
      */
-    void childStarted(GoalPtr goal, const std::set<int> & fds,
+    void childStarted(GoalPtr goal, const std::set<Child::CommChannel> & channels,
         bool inBuildSlot, bool respectTimeouts);
 
     /**
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
index cc67da786..60174d009 100644
--- a/src/libstore/local.mk
+++ b/src/libstore/local.mk
@@ -4,7 +4,7 @@ libstore_NAME = libnixstore
 
 libstore_DIR := $(d)
 
-libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc)
+libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc $(d)/build/*.cc)
 ifdef HOST_UNIX
   libstore_SOURCES += $(wildcard $(d)/unix/*.cc $(d)/unix/builtins/*.cc $(d)/unix/build/*.cc)
 endif
@@ -43,7 +43,7 @@ endif
 
 INCLUDE_libstore := -I $(d) -I $(d)/build
 ifdef HOST_UNIX
-  INCLUDE_libstore += -I $(d)/unix
+  INCLUDE_libstore += -I $(d)/unix -I $(d)/unix/build
 endif
 ifdef HOST_LINUX
   INCLUDE_libstore += -I $(d)/linux
diff --git a/src/libstore/unix/build/derivation-goal.cc b/src/libstore/unix/build/derivation-goal.cc
index 8d6e35015..004094015 100644
--- a/src/libstore/unix/build/derivation-goal.cc
+++ b/src/libstore/unix/build/derivation-goal.cc
@@ -1280,7 +1280,7 @@ bool DerivationGoal::isReadDesc(int fd)
     return fd == hook->builderOut.readSide.get();
 }
 
-void DerivationGoal::handleChildOutput(int fd, std::string_view data)
+void DerivationGoal::handleChildOutput(Descriptor fd, std::string_view data)
 {
     // local & `ssh://`-builds are dealt with here.
     auto isWrittenToLog = isReadDesc(fd);
@@ -1347,7 +1347,7 @@ void DerivationGoal::handleChildOutput(int fd, std::string_view data)
 }
 
 
-void DerivationGoal::handleEOF(int fd)
+void DerivationGoal::handleEOF(Descriptor fd)
 {
     if (!currentLogLine.empty()) flushLine();
     worker.wakeUp(shared_from_this());
diff --git a/src/libstore/unix/build/derivation-goal.hh b/src/libstore/unix/build/derivation-goal.hh
index ddb5ee1e3..be6eb50c4 100644
--- a/src/libstore/unix/build/derivation-goal.hh
+++ b/src/libstore/unix/build/derivation-goal.hh
@@ -2,7 +2,7 @@
 ///@file
 
 #include "parsed-derivations.hh"
-#include "lock.hh"
+#include "user-lock.hh"
 #include "outputs-spec.hh"
 #include "store-api.hh"
 #include "pathlocks.hh"
@@ -292,8 +292,8 @@ struct DerivationGoal : public Goal
     /**
      * Callback used by the worker to write to the log.
      */
-    void handleChildOutput(int fd, std::string_view data) override;
-    void handleEOF(int fd) override;
+    void handleChildOutput(Descriptor fd, std::string_view data) override;
+    void handleEOF(Descriptor fd) override;
     void flushLine();
 
     /**
diff --git a/src/libstore/unix/lock.cc b/src/libstore/unix/user-lock.cc
similarity index 99%
rename from src/libstore/unix/lock.cc
rename to src/libstore/unix/user-lock.cc
index 023c74e34..8057aa13e 100644
--- a/src/libstore/unix/lock.cc
+++ b/src/libstore/unix/user-lock.cc
@@ -1,4 +1,4 @@
-#include "lock.hh"
+#include "user-lock.hh"
 #include "file-system.hh"
 #include "globals.hh"
 #include "pathlocks.hh"
diff --git a/src/libstore/unix/lock.hh b/src/libstore/unix/user-lock.hh
similarity index 100%
rename from src/libstore/unix/lock.hh
rename to src/libstore/unix/user-lock.hh
diff --git a/src/libstore/windows/build.cc b/src/libstore/windows/build.cc
deleted file mode 100644
index 3eadc5bda..000000000
--- a/src/libstore/windows/build.cc
+++ /dev/null
@@ -1,37 +0,0 @@
-#include "store-api.hh"
-#include "build-result.hh"
-
-namespace nix {
-
-void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMode, std::shared_ptr<Store> evalStore)
-{
-    unsupported("buildPaths");
-}
-
-std::vector<KeyedBuildResult> Store::buildPathsWithResults(
-    const std::vector<DerivedPath> & reqs,
-    BuildMode buildMode,
-    std::shared_ptr<Store> evalStore)
-{
-    unsupported("buildPathsWithResults");
-}
-
-BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
-    BuildMode buildMode)
-{
-    unsupported("buildDerivation");
-}
-
-
-void Store::ensurePath(const StorePath & path)
-{
-    unsupported("ensurePath");
-}
-
-
-void Store::repairPath(const StorePath & path)
-{
-    unsupported("repairPath");
-}
-
-}
diff --git a/src/libstore/windows/pathlocks.cc b/src/libstore/windows/pathlocks.cc
index 738057f68..8a4d55e00 100644
--- a/src/libstore/windows/pathlocks.cc
+++ b/src/libstore/windows/pathlocks.cc
@@ -9,6 +9,8 @@
 
 namespace nix {
 
+using namespace nix::windows;
+
 void deleteLockFile(const Path & path, Descriptor desc)
 {
 
diff --git a/src/libutil/error.hh b/src/libutil/error.hh
index 0419f36d6..87d181c94 100644
--- a/src/libutil/error.hh
+++ b/src/libutil/error.hh
@@ -206,11 +206,11 @@ MakeError(SystemError, Error);
  *
  * Throw this, but prefer not to catch this, and catch `SystemError`
  * instead. This allows implementations to freely switch between this
- * and `WinError` without breaking catch blocks.
+ * and `windows::WinError` without breaking catch blocks.
  *
  * However, it is permissible to catch this and rethrow so long as
  * certain conditions are not met (e.g. to catch only if `errNo =
- * EFooBar`). In that case, try to also catch the equivalent `WinError`
+ * EFooBar`). In that case, try to also catch the equivalent `windows::WinError`
  * code.
  *
  * @todo Rename this to `PosixError` or similar. At this point Windows
@@ -248,7 +248,9 @@ public:
 };
 
 #ifdef _WIN32
-class WinError;
+namespace windows {
+    class WinError;
+}
 #endif
 
 /**
@@ -258,7 +260,7 @@ class WinError;
  */
 using NativeSysError =
 #ifdef _WIN32
-    WinError
+    windows::WinError
 #else
     SysError
 #endif
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 5ea27ccbe..36b99905a 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -136,7 +136,7 @@ size_t FdSource::readUnbuffered(char * data, size_t len)
     checkInterrupt();
     if (!::ReadFile(fd, data, len, &n, NULL)) {
         _good = false;
-        throw WinError("ReadFile when FdSource::readUnbuffered");
+        throw windows::WinError("ReadFile when FdSource::readUnbuffered");
     }
 #else
     ssize_t n;
diff --git a/src/libutil/windows/file-descriptor.cc b/src/libutil/windows/file-descriptor.cc
index 26f769b66..b5c21ad32 100644
--- a/src/libutil/windows/file-descriptor.cc
+++ b/src/libutil/windows/file-descriptor.cc
@@ -14,6 +14,8 @@
 
 namespace nix {
 
+using namespace nix::windows;
+
 std::string readFile(HANDLE handle)
 {
     LARGE_INTEGER li;
diff --git a/src/libutil/windows/users.cc b/src/libutil/windows/users.cc
index 1792ff1a1..db6c42df3 100644
--- a/src/libutil/windows/users.cc
+++ b/src/libutil/windows/users.cc
@@ -9,6 +9,8 @@
 
 namespace nix {
 
+using namespace nix::windows;
+
 std::string getUserName()
 {
     // Get the required buffer size
diff --git a/src/libutil/windows/windows-async-pipe.cc b/src/libutil/windows/windows-async-pipe.cc
new file mode 100644
index 000000000..7aae603bd
--- /dev/null
+++ b/src/libutil/windows/windows-async-pipe.cc
@@ -0,0 +1,43 @@
+#include "windows-async-pipe.hh"
+#include "windows-error.hh"
+
+namespace nix::windows {
+
+void AsyncPipe::createAsyncPipe(HANDLE iocp)
+{
+    // std::cerr << (format("-----AsyncPipe::createAsyncPipe(%x)") % iocp) << std::endl;
+
+    buffer.resize(0x1000);
+    memset(&overlapped, 0, sizeof(overlapped));
+
+    std::string pipeName = fmt("\\\\.\\pipe\\nix-%d-%p", GetCurrentProcessId(), (void *) this);
+
+    readSide = CreateNamedPipeA(
+        pipeName.c_str(), PIPE_ACCESS_INBOUND | FILE_FLAG_OVERLAPPED, PIPE_TYPE_BYTE, PIPE_UNLIMITED_INSTANCES, 0, 0,
+        INFINITE, NULL);
+    if (!readSide)
+        throw WinError("CreateNamedPipeA(%s)", pipeName);
+
+    HANDLE hIocp = CreateIoCompletionPort(readSide.get(), iocp, (ULONG_PTR) (readSide.get()) ^ 0x5555, 0);
+    if (hIocp != iocp)
+        throw WinError("CreateIoCompletionPort(%x[%s], %x, ...) returned %x", readSide.get(), pipeName, iocp, hIocp);
+
+    if (!ConnectNamedPipe(readSide.get(), &overlapped) && GetLastError() != ERROR_IO_PENDING)
+        throw WinError("ConnectNamedPipe(%s)", pipeName);
+
+    SECURITY_ATTRIBUTES psa2 = {0};
+    psa2.nLength = sizeof(SECURITY_ATTRIBUTES);
+    psa2.bInheritHandle = TRUE;
+
+    writeSide = CreateFileA(pipeName.c_str(), GENERIC_WRITE, 0, &psa2, OPEN_EXISTING, 0, NULL);
+    if (!readSide)
+        throw WinError("CreateFileA(%s)", pipeName);
+}
+
+void AsyncPipe::close()
+{
+    readSide.close();
+    writeSide.close();
+}
+
+}
diff --git a/src/libutil/windows/windows-async-pipe.hh b/src/libutil/windows/windows-async-pipe.hh
new file mode 100644
index 000000000..c980201a8
--- /dev/null
+++ b/src/libutil/windows/windows-async-pipe.hh
@@ -0,0 +1,20 @@
+#pragma once
+///@file
+
+#include "file-descriptor.hh"
+
+namespace nix::windows {
+
+class AsyncPipe
+{
+public:
+    AutoCloseFD writeSide, readSide;
+    OVERLAPPED overlapped;
+    DWORD got;
+    std::vector<unsigned char> buffer;
+
+    void createAsyncPipe(HANDLE iocp);
+    void close();
+};
+
+}
diff --git a/src/libutil/windows/windows-error.cc b/src/libutil/windows/windows-error.cc
index 26faaae6d..aead4af23 100644
--- a/src/libutil/windows/windows-error.cc
+++ b/src/libutil/windows/windows-error.cc
@@ -4,7 +4,7 @@
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 
-namespace nix {
+namespace nix::windows {
 
 std::string WinError::renderError(DWORD lastError)
 {
diff --git a/src/libutil/windows/windows-error.hh b/src/libutil/windows/windows-error.hh
index fdfd0f52c..624b4c4cb 100644
--- a/src/libutil/windows/windows-error.hh
+++ b/src/libutil/windows/windows-error.hh
@@ -5,7 +5,7 @@
 
 #include "error.hh"
 
-namespace nix {
+namespace nix::windows {
 
 /**
  * Windows Error type.