chore: auto obtain worker pid in gdb script

Author: steve-chavez

.gitignore

@@ -14,3 +14,4 @@ nix/nginx/logs/nginx.pid
 *.so
 nginx.pid
 tags
+net_worker.pid

docs/contributing.md

@@ -54,20 +54,11 @@ select net.http_get('http://localhost:3000/projects');
 
 ### GDB
 
-To debug the background worker, grab its PID from the logs:
+To debug the background worker, there's a script that wraps GDB. It automatically obtains the pid of the latest started worker:
 
 ```
 $ nix-shell
-$ net-with-pg-16 psql
-
-2024-09-02 20:16:26.905 -05 [1145879] INFO:  pg_net_worker started with a config of: pg_net.ttl=6 hours, pg_net.batch_size=200, pg_net.database_name=postgres
-```
-
-And use it like:
-
-```
-$ nix-shell
-$ sudo with-gdb -p 1145879
+$ sudo net-with-gdb
 ```
 
 ## Load Testing

nix/gdbScript.nix

@@ -1,12 +1,20 @@
-{ gdb, writeText, writeShellScriptBin } :
+{ gdb, writeText, writeShellScriptBin, pidFileName } :
 
 let
   file = writeText "gdbconf" ''
     # Do this so we can do `backtrace` once a segfault occurs. Otherwise once SIGSEGV is received the bgworker will quit and we can't backtrace.
     handle SIGSEGV stop nopass
   '';
   script = ''
-    ${gdb}/bin/gdb -x ${file} "$@"
+    set -euo pipefail
+
+    if [ ! -e ${pidFileName} ]
+    then
+      echo "The pg_net worker is not started. Exiting."
+      exit 1
+    fi
+    pid=$(cat ${pidFileName})
+    ${gdb}/bin/gdb -x ${file} -p ''$pid "$@"
   '';
 in
-writeShellScriptBin "with-gdb" script
+writeShellScriptBin "net-with-gdb" script

nix/pgScript.nix

@@ -1,4 +1,4 @@
-{ postgresql, writeShellScriptBin } :
+{ postgresql, writeShellScriptBin, gnused, pidFileName } :
 
 let
   ver = builtins.head (builtins.splitVersion postgresql.version);
@@ -14,7 +14,7 @@ let
     export PGUSER=postgres
     export PGDATABASE=postgres
 
-    trap 'pg_ctl stop -m i && rm -rf "$tmpdir"' sigint sigterm exit
+    trap 'pg_ctl stop -m i && rm -rf "$tmpdir" && rm ${pidFileName}' sigint sigterm exit
 
     PGTZ=UTC initdb --no-locale --encoding=UTF8 --nosync -U "$PGUSER"
 
@@ -26,6 +26,12 @@ let
 
     psql -v ON_ERROR_STOP=1 -c "create extension pg_net" -d postgres
 
+    psql -t -c "\o ${pidFileName}" -c "select pid from pg_stat_activity where backend_type ilike '%pg_net%'"
+
+    ${gnused}/bin/sed '/^''$/d;s/[[:blank:]]//g' -i ${pidFileName}
+
+    psql -f ${./bench.sql}
+
     "$@"
   '';
 in

shell.nix

@@ -6,6 +6,7 @@ with import (builtins.fetchTarball {
 mkShell {
   buildInputs =
     let
+      pidFileName = "net_worker.pid";
       supportedPgVersions = [
         postgresql_12
         postgresql_13
@@ -14,9 +15,9 @@ mkShell {
         postgresql_16
       ];
       pgWithExt = { pg }: pg.withPackages (p: [ (callPackage ./nix/pg_net.nix { postgresql = pg;}) ]);
-      extAll = map (x: callPackage ./nix/pgScript.nix { postgresql = pgWithExt { pg = x;}; }) supportedPgVersions;
+      extAll = map (x: callPackage ./nix/pgScript.nix { postgresql = pgWithExt { pg = x;}; inherit pidFileName;}) supportedPgVersions;
+      gdbScript = callPackage ./nix/gdbScript.nix {inherit pidFileName;};
       nginxCustom = callPackage ./nix/nginxCustom.nix {};
-      gdbScript = callPackage ./nix/gdbScript.nix {};
       nixopsScripts = callPackage ./nix/nixopsScripts.nix {};
       pythonDeps = with python3Packages; [
         pytest