From 18bb3df157f0b553f25d13e9e5f230889ebb412f Mon Sep 17 00:00:00 2001
From: Vitaly Cheptsov <4348897+vit9696@users.noreply.github.com>
Date: Sat, 2 Sep 2023 22:48:23 +0300
Subject: Fix race condition in MkdirFunc

---
 CHANGES.txt      |  4 ++++
 RELEASE.txt      |  2 ++
 SCons/Node/FS.py | 23 ++++++++++++++++-------
 3 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index e323e67..7986818 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -39,6 +39,10 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
     - Add arm64 to the MSVS supported architectures list for VS2017 and later to be
       consistent with the current documentation of MSVS_ARCH.
 
+  From Vitaly Cheptsov:
+    - Fix race condition in `Mkdir` which can happen when two `SConscript`
+      are processed simultaneously by two separate build commands.
+
   From William Deegan:
     - The --debug flag now has a 'json' option which will write information
       generated by --debug={count, memory, time, action-timestamps} and about
diff --git a/RELEASE.txt b/RELEASE.txt
index 8041949..b1e49ff 100644
--- a/RELEASE.txt
+++ b/RELEASE.txt
@@ -107,6 +107,8 @@ FIXES
   (Enabled/specified by SCONS_CACHE_MSVC_CONFIG).
   The existing cache will be discarded if there's a decode error reading it.
   It's possible there's a race condition creating this issue it in certain CI builds.
+- Fixed: race condition in `Mkdir` which can happen when two `SConscript`
+  are processed simultaneously by two separate build commands.
 
 IMPROVEMENTS
 ------------
diff --git a/SCons/Node/FS.py b/SCons/Node/FS.py
index 151a925..3162b21 100644
--- a/SCons/Node/FS.py
+++ b/SCons/Node/FS.py
@@ -335,13 +335,22 @@ Unlink = SCons.Action.Action(UnlinkFunc, None)
 
 def MkdirFunc(target, source, env) -> int:
     t = target[0]
-    # This os.path.exists test looks redundant, but it's possible
-    # when using Install() to install multiple dirs outside the
-    # source tree to get a case where t.exists() is true but
-    # the path does already exist, so this prevents spurious
-    # build failures in that case. See test/Install/multi-dir.
-    if not t.exists() and not os.path.exists(t.get_abspath()):
-        t.fs.mkdir(t.get_abspath())
+    # - It's possible when using Install() to install multiple
+    #   dirs outside the source tree to get a case where t.exists()
+    #   is false but the path does already exist.
+    # - It's also possible for multiple SCons processes to try to create
+    #   multiple build directories when processing SConscript files with
+    #   variant dirs.
+    # Catching OS exceptions and ensuring directory existence prevents
+    # build failures in these cases. See test/Install/multi-dir.
+
+    if not t.exists():
+        abs_path = t.get_abspath()
+        try:
+            t.fs.mkdir(abs_path)
+        except FileExistsError:
+            pass
+
     return 0
 
 Mkdir = SCons.Action.Action(MkdirFunc, None, presub=None)
-- 
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