unnamed threads: Obliterate

Ever read gdb output and you just kinda get a headache because you have
to infer what a thread is by reading the stack trace? It's not hard, but
we could also just never have to do that again, which is also not hard.

Sample:

(gdb) info thr
  Id   Target Id                    Frame
* 1    LWP 3719283 "nix-daemon"     0x00007e558587da0f in accept ()
   from target:/nix/store/c10zhkbp6jmyh0xc5kd123ga8yy2p4hk-glibc-2.39-52/lib/libc.so.6
  2    LWP 3719284 "signal handler" 0x00007e55857b2bea in sigtimedwait ()
   from target:/nix/store/c10zhkbp6jmyh0xc5kd123ga8yy2p4hk-glibc-2.39-52/lib/libc.so.6

The API design for this is forced by the macOS pthread_setname_np only
being able to change the current thread's name, but if we just conform
everything to that, it works everywhere.

Change-Id: I2b1d6ed41e3c94170cb0b4e73ad66f239ebd9c88

doc/manual/rl-next/thread-names.md

@@ -0,0 +1,17 @@
+---
+synopsis: All Lix threads are named
+cls: [2210]
+category: Development
+credits: [jade]
+---
+
+Lix now sets thread names on all of its secondary threads, which will make debugger usage slightly nicer and easier.
+
+```
+(gdb) info thr
+  Id   Target Id                    Frame
+* 1    LWP 3719283 "nix-daemon"     0x00007e558587da0f in accept ()
+   from target:/nix/store/c10zhkbp6jmyh0xc5kd123ga8yy2p4hk-glibc-2.39-52/lib/libc.so.6
+  2    LWP 3719284 "signal handler" 0x00007e55857b2bea in sigtimedwait ()
+   from target:/nix/store/c10zhkbp6jmyh0xc5kd123ga8yy2p4hk-glibc-2.39-52/lib/libc.so.6
+```

src/libmain/progress-bar.cc

@@ -4,6 +4,7 @@
 #include "lix/libstore/names.hh"
 #include "lix/libutil/terminal.hh"
 #include "lix/libutil/strings.hh"
+#include "lix/libutil/thread-name.hh"
 
 #include <map>
 #include <thread>
@@ -84,6 +85,7 @@ void ProgressBar::resume()
     if (state->paused > 0) return; // recursive pause, wait for the parents to resume too
     state->haveUpdate = true;
     updateThread = std::thread([&]() {
+        setCurrentThreadName("progress bar");
         auto state(state_.lock());
         auto nextWakeup = A_LONG_TIME;
         while (state->paused == 0) {

src/libstore/binary-cache-store.cc

@@ -196,7 +196,7 @@ ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
 
         if (narAccessor->stat(buildIdDir).type == FSAccessor::tDirectory) {
 
-            ThreadPool threadPool(25);
+            ThreadPool threadPool("write debuginfo pool", 25);
 
             auto doFile = [&](std::string member, std::string key, std::string target) {
                 checkInterrupt();

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

@@ -19,6 +19,7 @@
 #include "lix/libutil/unix-domain-socket.hh"
 #include "lix/libutil/mount.hh"
 #include "lix/libutil/strings.hh"
+#include "lix/libutil/thread-name.hh"
 
 #include <regex>
 #include <queue>
@@ -1224,6 +1225,7 @@ void LocalDerivationGoal::startDaemon()
     chownToBuilder(socketPath);
 
     daemonThread = std::thread([this, store]() {
+        setCurrentThreadName("recursive nix daemon");
 
         while (true) {
 
@@ -1244,6 +1246,7 @@ void LocalDerivationGoal::startDaemon()
             debug("received daemon connection");
 
             auto workerThread = std::thread([store, remote{std::move(remote)}]() {
+                setCurrentThreadName("recursive nix worker");
                 FdSource from(remote.get());
                 FdSink to(remote.get());
                 try {

src/libstore/filetransfer.cc

@@ -5,6 +5,7 @@
 #include "lix/libstore/s3.hh"
 #include "lix/libutil/signals.hh"
 #include "lix/libutil/strings.hh"
+#include "lix/libutil/thread-name.hh"
 #include <cstddef>
 
 #include <cstdio>
@@ -454,7 +455,10 @@ struct curlFileTransfer : public FileTransfer
         curl_multi_setopt(curlm.get(), CURLMOPT_MAX_TOTAL_CONNECTIONS,
             fileTransferSettings.httpConnections.get());
 
-        workerThread = std::thread([&]() { workerThreadEntry(); });
+        workerThread = std::thread([&]() {
+            setCurrentThreadName("curlFileTransfer worker");
+            workerThreadEntry();
+        });
     }
 
     ~curlFileTransfer()

src/libstore/gc.cc

@@ -6,6 +6,7 @@
 #include "lix/libutil/finally.hh"
 #include "lix/libutil/unix-domain-socket.hh"
 #include "lix/libutil/strings.hh"
+#include "lix/libutil/thread-name.hh"
 
 #include <queue>
 #include <regex>
@@ -420,7 +421,10 @@ class GCOperation {
             throw SysError("making socket '%1%' non-blocking", socketPath);
         }
 
-        serverThread = std::thread([this]() { runServerThread(); });
+        serverThread = std::thread([this]() {
+            setCurrentThreadName("gc server");
+            runServerThread();
+        });
     }
 
     void addTempRoot(std::string rootHashPart)
@@ -491,6 +495,7 @@ void GCOperation::runServerThread()
             /* Process the connection in a separate thread. */
             auto fdClient_ = fdClient.get();
             std::thread clientThread([&, fdClient = std::move(fdClient)]() {
+                setCurrentThreadName("gc server connection");
                 Finally cleanup([&]() {
                     auto conn(connections.lock());
                     auto i = conn->find(fdClient.get());
@@ -900,6 +905,7 @@ void LocalStore::autoGC(bool sync)
         future = state->gcFuture = promise.get_future().share();
 
         std::thread([promise{std::move(promise)}, this, avail, getAvail]() mutable {
+            setCurrentThreadName("auto gc");
 
             try {
 

src/libstore/misc.cc

@@ -86,7 +86,7 @@ void Store::queryMissing(const std::vector<DerivedPath> & targets,
     downloadSize_ = narSize_ = 0;
 
     // FIXME: make async.
-    ThreadPool pool(fileTransferSettings.httpConnections);
+    ThreadPool pool("queryMissing pool", fileTransferSettings.httpConnections);
 
     struct State
     {

src/libstore/remote-store.cc

@@ -17,6 +17,7 @@
 #include "lix/libutil/logging.hh"
 #include "lix/libstore/filetransfer.hh"
 #include "lix/libutil/strings.hh"
+#include "lix/libutil/thread-name.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -971,6 +972,7 @@ void RemoteStore::ConnectionHandle::withFramedSink(std::function<void(Sink & sin
        thread. */
     std::thread stderrThread([&]()
     {
+        setCurrentThreadName("remote stderr thread");
         try {
             ReceiveInterrupts receiveInterrupts;
             processStderr(nullptr, nullptr, false);

src/libstore/store-api.cc

@@ -306,7 +306,7 @@ void Store::addMultipleToStore(
         act.progress(nrDone, pathsToCopy.size(), nrRunning, nrFailed);
     };
 
-    ThreadPool pool;
+    ThreadPool pool{"addMultipleToStore pool"};
 
     processGraph<StorePath>(pool,
         storePathsToAdd,
@@ -835,7 +835,7 @@ StorePathSet Store::queryValidPaths(const StorePathSet & paths, SubstituteFlag m
     Sync<State> state_(State{paths.size(), StorePathSet()});
 
     std::condition_variable wakeup;
-    ThreadPool pool;
+    ThreadPool pool{"queryValidPaths pool"};
 
     auto doQuery = [&](const StorePath & path) {
         checkInterrupt();
@@ -1136,7 +1136,7 @@ std::map<StorePath, StorePath> copyPaths(
     }
     auto pathsMap = copyPaths(srcStore, dstStore, storePaths, repair, checkSigs, substitute);
 
-    ThreadPool pool;
+    ThreadPool pool{"copyPaths pool"};
 
     try {
         // Copy the realisation closure

src/libutil/meson.build

@@ -38,6 +38,7 @@ libutil_sources = files(
   'suggestions.cc',
   'tarfile.cc',
   'terminal.cc',
+  'thread-name.cc',
   'thread-pool.cc',
   'unix-domain-socket.cc',
   'url.cc',
@@ -118,6 +119,7 @@ libutil_headers = files(
   'sync.hh',
   'tarfile.hh',
   'terminal.hh',
+  'thread-name.hh',
   'thread-pool.hh',
   'topo-sort.hh',
   'types.hh',

src/libutil/monitor-fd.hh

@@ -4,15 +4,14 @@
 #include <thread>
 #include <atomic>
 
-#include <cstdlib>
 #include <poll.h>
 #include <sys/types.h>
 #include <unistd.h>
-#include <signal.h>
 
 #include "lix/libutil/error.hh"
 #include "lix/libutil/file-descriptor.hh"
 #include "lix/libutil/signals.hh"
+#include "lix/libutil/thread-name.hh"
 
 namespace nix {
 
@@ -34,6 +33,7 @@ public:
         auto &quit_ = this->quit;
         int terminateFd = terminatePipe.readSide.get();
         thread = std::thread([fd, terminateFd, &quit_]() {
+            setCurrentThreadName("MonitorFdHup");
             while (!quit_) {
                 /* Wait indefinitely until a POLLHUP occurs. */
                 struct pollfd fds[2];

src/libutil/signals.cc

@@ -2,6 +2,7 @@
 #include "lix/libutil/error.hh"
 #include "lix/libutil/sync.hh"
 #include "lix/libutil/terminal.hh"
+#include "lix/libutil/thread-name.hh"
 
 #include <map>
 #include <thread>
@@ -49,6 +50,7 @@ static Sync<InterruptCallbacks> _interruptCallbacks;
 
 static void signalHandlerThread(sigset_t set)
 {
+    setCurrentThreadName("signal handler");
     while (true) {
         int signal = 0;
         sigwait(&set, &signal);

src/libutil/thread-name.cc

@@ -0,0 +1,20 @@
+#include <pthread.h>
+#if defined(__FreeBSD__) || defined(__OpenBSD__)
+#include <pthread_np.h>
+#endif
+
+namespace nix {
+
+void setCurrentThreadName(const char * name)
+{
+    // https://stackoverflow.com/questions/2369738/how-to-set-the-name-of-a-thread-in-linux-pthreads/7989973
+#if defined(__linux__)
+    pthread_setname_np(pthread_self(), name);
+#elif defined(__APPLE__)
+    pthread_setname_np(name);
+#elif defined(__FreeBSD__) || defined(__OpenBSD__)
+    pthread_set_name_np(pthread_self(), name);
+#endif
+}
+
+}

src/libutil/thread-name.hh

@@ -0,0 +1,12 @@
+#pragma once
+///@file
+
+namespace nix {
+
+/**
+ * Sets the name of the current operating system thread for the benefit of
+ * debuggers.
+ */
+void setCurrentThreadName(const char * name);
+
+}

src/libutil/thread-pool.cc

@@ -1,11 +1,12 @@
 #include "lix/libutil/thread-pool.hh"
 #include "lix/libutil/logging.hh"
 #include "lix/libutil/signals.hh"
+#include "lix/libutil/thread-name.hh"
 
 namespace nix {
 
-ThreadPool::ThreadPool(size_t _maxThreads)
+ThreadPool::ThreadPool(const char * name, size_t _maxThreads)
-    : maxThreads(_maxThreads)
+    : maxThreads(_maxThreads), name(name)
 {
     if (!maxThreads) {
         maxThreads = std::thread::hardware_concurrency();
@@ -81,8 +82,10 @@ void ThreadPool::doWork(bool mainThread)
 {
     ReceiveInterrupts receiveInterrupts;
 
-    if (!mainThread)
+    if (!mainThread) {
+        setCurrentThreadName(this->name);
         interruptCheck = [&]() { return (bool) quit; };
+    }
 
     bool didWork = false;
     std::exception_ptr exc;

src/libutil/thread-pool.hh

@@ -22,7 +22,7 @@ class ThreadPool
 {
 public:
 
-    ThreadPool(size_t maxThreads = 0);
+    ThreadPool(const char * name, size_t maxThreads = 0);
 
     ~ThreadPool();
 
@@ -56,6 +56,8 @@ private:
 
     size_t maxThreads;
 
+    const char * name;
+
     struct State
     {
         std::queue<work_t> pending;

src/nix/sigs.cc

@@ -38,7 +38,7 @@ struct CmdCopySigs : StorePathsCommand
         for (auto & s : substituterUris)
             substituters.push_back(openStore(s));
 
-        ThreadPool pool;
+        ThreadPool pool{"CopySigs pool"};
 
         std::string doneLabel = "done";
         std::atomic<size_t> added{0};

src/nix/verify.cc

@@ -79,7 +79,7 @@ struct CmdVerify : StorePathsCommand
             act.progress(done, storePaths.size(), active, failed);
         };
 
-        ThreadPool pool;
+        ThreadPool pool{"Verify pool"};
 
         auto doPath = [&](const StorePath & storePath) {
             try {

tests/unit/libstore/filetransfer.cc

@@ -1,5 +1,6 @@
 #include "lix/libstore/filetransfer.hh"
 #include "lix/libutil/compression.hh"
+#include "lix/libutil/thread-name.hh"
 
 #include <cstdint>
 #include <exception>
@@ -90,6 +91,7 @@ serveHTTP(std::vector<Reply> replies)
 
     std::thread(
         [replies, at{0}](AutoCloseFD socket, AutoCloseFD trigger) mutable {
+            setCurrentThreadName("test httpd server");
             while (true) {
                 pollfd pfds[2] = {
                     {
@@ -120,6 +122,7 @@ serveHTTP(std::vector<Reply> replies)
                 const auto & reply = replies[at++ % replies.size()];
 
                 std::thread([=, conn{std::move(conn)}] {
+                    setCurrentThreadName("test httpd connection");
                     auto send = [&](std::string_view bit) {
                         while (!bit.empty()) {
                             auto written = ::send(conn.get(), bit.data(), bit.size(), MSG_NOSIGNAL);