From 67aace0024c8421c7419c02d488d48426eb2a6b0 Mon Sep 17 00:00:00 2001
From: Tugdual Saunier <tugdual.saunier@gmail.com>
Date: Thu, 12 Jun 2025 11:42:37 +0200
Subject: [PATCH 1/2] do not truncate log files on each LogWriter calls

We used to have a single concurrent usage of the `LogWriter`, but this is not the case anymore since b29665f7afcba0a71a30077d3516aa6076908924.
Because of this we now loose the runner logs as he file is being truncated during the `buildCmd` call when the LogWrited is fetched.

To fix this i propose to instantiate the LogWriter once which will effectively truncate the file only once per `server:start` launch.
---
 local/pid/pidfile.go | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/local/pid/pidfile.go b/local/pid/pidfile.go
index db0ee4fd..3edf706a 100644
--- a/local/pid/pidfile.go
+++ b/local/pid/pidfile.go
@@ -49,6 +49,7 @@ type PidFile struct {
 	CustomName string   `json:"name"`
 
 	path string
+	lw   io.WriteCloser // log writer, used to write logs to the log file
 }
 
 func New(dir string, args []string) *PidFile {
@@ -258,15 +259,24 @@ func (p *PidFile) LogReader() (io.ReadCloser, error) {
 }
 
 func (p *PidFile) LogWriter() (io.WriteCloser, error) {
+	// instantiate the log writer only once per process lifetime, this is useful
+	// to have a single truncate (and thus a clean log file) at the beginning of
+	// the process management but not truncate the log file when the process is
+	// restarted.
+	if p.lw != nil {
+		return p.lw, nil
+	}
+
 	logFile := p.LogFile()
-	if err := os.MkdirAll(filepath.Dir(logFile), 0755); err != nil {
+	err := os.MkdirAll(filepath.Dir(logFile), 0755)
+	if err != nil {
 		return nil, err
 	}
-	w, err := os.OpenFile(logFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
+	p.lw, err = os.OpenFile(logFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
 	if err != nil {
 		return nil, err
 	}
-	return w, nil
+	return p.lw, nil
 }
 
 func (p *PidFile) Binary() string {

From 606fd41e3f88bd50266d406ac4921bd47f95e86c Mon Sep 17 00:00:00 2001
From: Tugdual Saunier <tugdual.saunier@gmail.com>
Date: Sat, 14 Jun 2025 12:31:41 +0200
Subject: [PATCH 2/2] use sync.Once to make `PidFile.LogWriter` calls safe

---
 local/pid/pidfile.go | 42 +++++++++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/local/pid/pidfile.go b/local/pid/pidfile.go
index 3edf706a..b044c8a0 100644
--- a/local/pid/pidfile.go
+++ b/local/pid/pidfile.go
@@ -27,6 +27,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -49,7 +50,9 @@ type PidFile struct {
 	CustomName string   `json:"name"`
 
 	path string
-	lw   io.WriteCloser // log writer, used to write logs to the log file
+
+	lwInit sync.Once      // used to ensure that the log writer is only created once
+	lw     io.WriteCloser // log writer, used to write logs to the log file
 }
 
 func New(dir string, args []string) *PidFile {
@@ -258,25 +261,34 @@ func (p *PidFile) LogReader() (io.ReadCloser, error) {
 	return r, nil
 }
 
+// LogWriter returns a writer to write logs to the log file. It creates the log
+// file if it does not exist, and truncates it if it does. It is safe to call
+// this method multiple times, it will only create the log file once per process
+// lifetime: it is useful to have a single truncation (and thus a clean log
+// file) at the beginning of the process management but not to truncate the log
+// file when the process is restarted.
+// Please note this method might not return a writer even if the error is nil
+// (the error is returned only for the first call).
 func (p *PidFile) LogWriter() (io.WriteCloser, error) {
-	// instantiate the log writer only once per process lifetime, this is useful
-	// to have a single truncate (and thus a clean log file) at the beginning of
-	// the process management but not truncate the log file when the process is
-	// restarted.
-	if p.lw != nil {
-		return p.lw, nil
-	}
+	var err error
+
+	p.lwInit.Do(func() {
+		logFile := p.LogFile()
+		if err = errors.WithStack(os.MkdirAll(filepath.Dir(logFile), 0755)); err != nil {
+			return
+		}
+		p.lw, err = os.OpenFile(logFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
+		if err != nil {
+			err = errors.WithStack(err)
+			return
+		}
+	})
 
-	logFile := p.LogFile()
-	err := os.MkdirAll(filepath.Dir(logFile), 0755)
-	if err != nil {
-		return nil, err
-	}
-	p.lw, err = os.OpenFile(logFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
 	if err != nil {
 		return nil, err
 	}
-	return p.lw, nil
+
+	return p.lw, err
 }
 
 func (p *PidFile) Binary() string {