libutil: remove callback.hh

it's no longer used. it really shouldn't have existed this long since it
was just a mashup of both std::promise and std::packaged_task in a shape
that makes composition unnecessarily difficult. all but a single case of
Callback pattern calls were fully synchronous anyway, and even this sole
outlier was by far not important enough to justify the extra complexity.

Change-Id: I208aec4572bf2501cdbd0f331f27d505fca3a62f

src/libstore/binary-cache-store.cc

@@ -11,7 +11,6 @@
 #include "nar-accessor.hh"
 #include "thread-pool.hh"
 #include "signals.hh"
-#include "callback.hh"
 
 #include <chrono>
 #include <future>

src/libstore/build/derivation-goal.cc

@@ -11,7 +11,6 @@
 #include "common-protocol.hh"
 #include "common-protocol-impl.hh"
 #include "topo-sort.hh"
-#include "callback.hh"
 #include "local-store.hh" // TODO remove, along with remaining downcasts
 #include "logging-json.hh"
 

src/libstore/build/drv-output-substitution-goal.cc

@@ -2,7 +2,6 @@
 #include "finally.hh"
 #include "worker.hh"
 #include "substitution-goal.hh"
-#include "callback.hh"
 #include "signals.hh"
 
 namespace nix {

src/libstore/build/local-derivation-goal.cc

@@ -11,7 +11,6 @@
 #include "compression.hh"
 #include "daemon.hh"
 #include "topo-sort.hh"
-#include "callback.hh"
 #include "json-utils.hh"
 #include "cgroup.hh"
 #include "personality.hh"

src/libstore/dummy-store.cc

@@ -1,5 +1,4 @@
 #include "store-api.hh"
-#include "callback.hh"
 
 namespace nix {
 

src/libstore/filetransfer.cc

@@ -6,7 +6,6 @@
 #include "signals.hh"
 #include "compression.hh"
 #include "finally.hh"
-#include "callback.hh"
 
 #if ENABLE_S3
 #include <aws/core/client/ClientConfiguration.h>

src/libstore/http-binary-cache-store.cc

@@ -2,7 +2,6 @@
 #include "filetransfer.hh"
 #include "globals.hh"
 #include "nar-info-disk-cache.hh"
-#include "callback.hh"
 
 namespace nix {
 

src/libstore/legacy-ssh-store.cc

@@ -9,7 +9,6 @@
 #include "path-with-outputs.hh"
 #include "ssh.hh"
 #include "derivations.hh"
-#include "callback.hh"
 
 namespace nix {
 

src/libstore/local-store.cc

@@ -6,7 +6,6 @@
 #include "derivations.hh"
 #include "nar-info.hh"
 #include "references.hh"
-#include "callback.hh"
 #include "topo-sort.hh"
 #include "signals.hh"
 #include "finally.hh"

src/libstore/misc.cc

@@ -5,7 +5,6 @@
 #include "store-api.hh"
 #include "thread-pool.hh"
 #include "topo-sort.hh"
-#include "callback.hh"
 #include "closure.hh"
 #include "filetransfer.hh"
 

src/libstore/remote-store.cc

@@ -15,7 +15,6 @@
 #include "pool.hh"
 #include "finally.hh"
 #include "logging.hh"
-#include "callback.hh"
 #include "filetransfer.hh"
 #include <nlohmann/json.hpp>
 

src/libstore/store-api.cc

@@ -9,7 +9,6 @@
 #include "url.hh"
 #include "references.hh"
 #include "archive.hh"
-#include "callback.hh"
 #include "remote-store.hh"
 #include "signals.hh"
 // FIXME this should not be here, see TODO below on

src/libutil/callback.hh

@@ -1,49 +0,0 @@
-#pragma once
-///@file
-
-#include <future>
-#include <functional>
-
-namespace nix {
-
-/**
- * A callback is a wrapper around a lambda that accepts a valid of
- * type T or an exception. (We abuse std::future<T> to pass the value or
- * exception.)
- */
-template<typename T>
-class Callback
-{
-    std::function<void(std::future<T>)> fun;
-    std::atomic_flag done = ATOMIC_FLAG_INIT;
-
-public:
-
-    Callback(std::function<void(std::future<T>)> fun) : fun(fun) { }
-
-    Callback(Callback && callback) : fun(std::move(callback.fun))
-    {
-        auto prev = callback.done.test_and_set();
-        if (prev) done.test_and_set();
-    }
-
-    void operator()(T && t) noexcept
-    {
-        auto prev = done.test_and_set();
-        assert(!prev);
-        std::promise<T> promise;
-        promise.set_value(std::move(t));
-        fun(promise.get_future());
-    }
-
-    void rethrow(const std::exception_ptr & exc = std::current_exception()) noexcept
-    {
-        auto prev = done.test_and_set();
-        assert(!prev);
-        std::promise<T> promise;
-        promise.set_exception(exc);
-        fun(promise.get_future());
-    }
-};
-
-}

src/libutil/meson.build

@@ -43,7 +43,6 @@ libutil_headers = files(
   'args/root.hh',
   'args.hh',
   'box_ptr.hh',
-  'callback.hh',
   'canon-path.hh',
   'cgroup.hh',
   'chunked-vector.hh',

src/libutil/util.hh

@@ -836,10 +836,6 @@ std::optional<typename T::value_type> pop(T & c)
 }
 
 
-template<typename T>
-class Callback;
-
-
 /**
  * A RAII helper that increments a counter on construction and
  * decrements it on destruction.