From a27faabd0a3fc0a693433fa5b277587127c14fb3 Mon Sep 17 00:00:00 2001
From: John Soo <john.soo@arista.com>
Date: Thu, 21 Apr 2022 10:46:38 -0700
Subject: [PATCH] Use Proc struct to manage forked processes.

Cleans up zombie processes.
---
 src/nix-eval-jobs.cc | 56 +++++++++++---------------------------------
 1 file changed, 14 insertions(+), 42 deletions(-)

diff --git a/src/nix-eval-jobs.cc b/src/nix-eval-jobs.cc
index 045577b..d71cf8d 100644
--- a/src/nix-eval-jobs.cc
+++ b/src/nix-eval-jobs.cc
@@ -177,8 +177,7 @@ static void worker(
     EvalState & state,
     Bindings & autoArgs,
     AutoCloseFD & to,
-    AutoCloseFD & from,
-    const Path &gcRootsDir)
+    AutoCloseFD & from)
 {
     auto vRoot = topLevelValue(state, autoArgs);
 
@@ -243,8 +242,8 @@ static void worker(
                 /* Register the derivation as a GC root.  !!! This
                    registers roots for jobs that we may have already
                    done. */
-                if (gcRootsDir != "") {
-                    Path root = gcRootsDir + "/" + std::string(baseNameOf(drvPath));
+                if (myArgs.gcRootsDir != "") {
+                    Path root = myArgs.gcRootsDir + "/" + std::string(baseNameOf(drvPath));
                     if (!pathExists(root))
                         localStore->addPermRoot(storePath, root);
                 }
@@ -391,47 +390,18 @@ int main(int argc, char * * argv)
         auto handler = [&]()
         {
             try {
-                pid_t pid = -1;
-                AutoCloseFD from, to;
+                std::optional<std::unique_ptr<Proc>> proc_;
 
                 while (true) {
 
-                    /* Start a new worker process if necessary. */
-                    if (pid == -1) {
-                        Pipe toPipe, fromPipe;
-                        toPipe.create();
-                        fromPipe.create();
-                        pid = startProcess(
-                            [&,
-                             to{std::make_shared<AutoCloseFD>(std::move(fromPipe.writeSide))},
-                             from{std::make_shared<AutoCloseFD>(std::move(toPipe.readSide))}
-                            ]()
-                            {
-                                try {
-                                    EvalState state(myArgs.searchPath, openStore());
-                                    Bindings & autoArgs = *myArgs.getAutoArgs(state);
-                                    worker(state, autoArgs, *to, *from, myArgs.gcRootsDir);
-                                } catch (Error & e) {
-                                    nlohmann::json err;
-                                    auto msg = e.msg();
-                                    err["error"] = filterANSIEscapes(msg, true);
-                                    printError(msg);
-                                    writeLine(to->get(), err.dump());
-                                    // Don't forget to print it into the STDERR log, this is
-                                    // what's shown in the Hydra UI.
-                                    writeLine(to->get(), "restart");
-                                }
-                            },
-                            ProcessOptions { .allowVfork = false });
-                        from = std::move(fromPipe.readSide);
-                        to = std::move(toPipe.writeSide);
-                        debug("created worker process %d", pid);
-                    }
+                    auto proc = proc_.has_value()
+                        ? std::move(proc_.value())
+                        : std::make_unique<Proc>(worker);
 
                     /* Check whether the existing worker process is still there. */
-                    auto s = readLine(from.get());
+                    auto s = readLine(proc->from.get());
                     if (s == "restart") {
-                        pid = -1;
+                        proc_ = std::nullopt;
                         continue;
                     } else if (s != "next") {
                         auto json = nlohmann::json::parse(s);
@@ -445,7 +415,7 @@ int main(int argc, char * * argv)
                         checkInterrupt();
                         auto state(state_.lock());
                         if ((state->todo.empty() && state->active.empty()) || state->exc) {
-                            writeLine(to.get(), "exit");
+                            writeLine(proc->to.get(), "exit");
                             return;
                         }
                         if (!state->todo.empty()) {
@@ -458,10 +428,10 @@ int main(int argc, char * * argv)
                     }
 
                     /* Tell the worker to evaluate it. */
-                    writeLine(to.get(), "do " + attrPath);
+                    writeLine(proc->to.get(), "do " + attrPath);
 
                     /* Wait for the response. */
-                    auto respString = readLine(from.get());
+                    auto respString = readLine(proc->from.get());
                     auto response = nlohmann::json::parse(respString);
 
                     /* Handle the response. */
@@ -476,6 +446,8 @@ int main(int argc, char * * argv)
                         std::cout << respString << "\n" << std::flush;
                     }
 
+                    proc_ = std::move(proc);
+
                     /* Add newly discovered job names to the queue. */
                     {
                         auto state(state_.lock());