From e8fa0a3d2025509fcddc59fc618e91371542cf87 Mon Sep 17 00:00:00 2001
From: Samuel Dobson <dobsonsa68@gmail.com>
Date: Sun, 19 Apr 2020 11:07:14 +1200
Subject: Fix WSL file locking by using flock instead of fcntl

Co-authored-by: sipa <pieter@wuille.net>
---
 src/fs.cpp | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

(limited to 'src')

diff --git a/src/fs.cpp b/src/fs.cpp
index 066c6c10d3..e68c97b3ca 100644
--- a/src/fs.cpp
+++ b/src/fs.cpp
@@ -6,6 +6,9 @@
 
 #ifndef WIN32
 #include <fcntl.h>
+#include <string>
+#include <sys/file.h>
+#include <sys/utsname.h>
 #else
 #ifndef NOMINMAX
 #define NOMINMAX
@@ -47,20 +50,38 @@ FileLock::~FileLock()
     }
 }
 
+static bool IsWSL()
+{
+    struct utsname uname_data;
+    return uname(&uname_data) == 0 && std::string(uname_data.version).find("Microsoft") != std::string::npos;
+}
+
 bool FileLock::TryLock()
 {
     if (fd == -1) {
         return false;
     }
-    struct flock lock;
-    lock.l_type = F_WRLCK;
-    lock.l_whence = SEEK_SET;
-    lock.l_start = 0;
-    lock.l_len = 0;
-    if (fcntl(fd, F_SETLK, &lock) == -1) {
-        reason = GetErrorReason();
-        return false;
+
+    // Exclusive file locking is broken on WSL using fcntl (issue #18622)
+    // This workaround can be removed once the bug on WSL is fixed
+    static const bool is_wsl = IsWSL();
+    if (is_wsl) {
+        if (flock(fd, LOCK_EX | LOCK_NB) == -1) {
+            reason = GetErrorReason();
+            return false;
+        }
+    } else {
+        struct flock lock;
+        lock.l_type = F_WRLCK;
+        lock.l_whence = SEEK_SET;
+        lock.l_start = 0;
+        lock.l_len = 0;
+        if (fcntl(fd, F_SETLK, &lock) == -1) {
+            reason = GetErrorReason();
+            return false;
+        }
     }
+
     return true;
 }
 #else
-- 
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