parallelize artifact downloads

src/Operations.jl

@@ -826,16 +826,29 @@ function download_artifacts(env::EnvCache;
         pkg_root === nothing || push!(pkg_roots, pkg_root)
     end
     push!(pkg_roots, dirname(env.project_file))
+    used_artifact_tomls = Set{String}()
+    download_jobs = Channel{Function}(Inf)
     for pkg_root in pkg_roots
         for (artifacts_toml, artifacts) in collect_artifacts(pkg_root; platform)
             # For each Artifacts.toml, install each artifact we've collected from it
             for name in keys(artifacts)
-                ensure_artifact_installed(name, artifacts[name], artifacts_toml;
+                # @info name
+                push!(download_jobs,
+                    () -> ensure_artifact_installed(name, artifacts[name], artifacts_toml;
                                             verbose, quiet_download=!(usable_io(io)), io=io)
+                )
             end
-            write_env_usage(artifacts_toml, "artifact_usage.toml")
+            push!(used_artifact_tomls, artifacts_toml)
         end
     end
+    close(download_jobs)
+    @sync for f in download_jobs
+        Threads.@spawn f()
+    end
+
+    for f in used_artifact_tomls
+        write_env_usage(f, "artifact_usage.toml")
+    end
 end
 
 function check_artifacts_downloaded(pkg_root::String; platform::AbstractPlatform=HostPlatform())

src/Pkg.jl

@@ -17,7 +17,7 @@ export UpgradeLevel, UPLEVEL_MAJOR, UPLEVEL_MINOR, UPLEVEL_PATCH
 export PreserveLevel, PRESERVE_TIERED_INSTALLED, PRESERVE_TIERED, PRESERVE_ALL_INSTALLED, PRESERVE_ALL, PRESERVE_DIRECT, PRESERVE_SEMVER, PRESERVE_NONE
 export Registry, RegistrySpec
 
-public activate, add, build, compat, develop, free, gc, generate, instantiate, 
+public activate, add, build, compat, develop, free, gc, generate, instantiate,
        pin, precompile, redo, rm, resolve, status, test, undo, update, why
 
 depots() = Base.DEPOT_PATH

src/PlatformEngines.jl

@@ -282,7 +282,7 @@ function download(
         (total, now) -> nothing
     end
     try
-        Downloads.download(url, dest; headers, progress)
+        Downloads.download(url, dest; headers, progress, downloader=Downloads.Downloader(; grace=0))
     finally
         do_fancy && end_progress(io, bar)
     end