From 205c54bf10f4b0fdce64c5dace5c5a86de27d248 Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Tue, 7 Jul 2020 11:52:40 +0300
Subject: On Windows make fdopen() to retry for a second on
 ERROR_SHARING_VIOLATION error

---
 libbutl/fdstream.cxx   | 36 +++++++++++++++++++++++++++++++++---
 libbutl/filesystem.cxx |  5 ++++-
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/libbutl/fdstream.cxx b/libbutl/fdstream.cxx
index 9f54852..b12ce78 100644
--- a/libbutl/fdstream.cxx
+++ b/libbutl/fdstream.cxx
@@ -1123,9 +1123,39 @@ namespace butl
     //
     of |= _O_NOINHERIT;
 
-    int fd (pass_perm
-            ? _sopen (f, of, _SH_DENYNO, pf)
-            : _sopen (f, of, _SH_DENYNO));
+    int fd;
+
+    // For reasons unknown an attempt to open an existing file for writing
+    // sometimes ends up with the EACCES POSIX error which is presumably a
+    // translation of the ERROR_SHARING_VIOLATION system error returned by the
+    // underlying CreateFile() function call (see mventry() for details). If
+    // that's the case, we will keep trying to open the file for a second.
+    //
+    for (size_t i (0); i < 11; ++i)
+    {
+      // Sleep 100 milliseconds before the open retry.
+      //
+      if (i != 0)
+        Sleep (100);
+
+      fd = pass_perm
+           ? _sopen (f, of, _SH_DENYNO, pf)
+           : _sopen (f, of, _SH_DENYNO);
+
+      // Note that MSVCRT's _sopen() calls CreateFile() underneath,
+      // translating the system error to POSIX on failure and bailing out
+      // afterwords. Thus, we can query the original error code on _sopen()
+      // failure.
+      //
+      // Note that MinGW's _sopen() is just a stub forwarding the call to the
+      // (publicly available) MSVCRT's implementation.
+      //
+      if (!(fd == -1        &&
+            out             &&
+            errno == EACCES &&
+            GetLastError () == ERROR_SHARING_VIOLATION))
+        break;
+    }
 
 #endif
 
diff --git a/libbutl/filesystem.cxx b/libbutl/filesystem.cxx
index f246214..f145ee7 100644
--- a/libbutl/filesystem.cxx
+++ b/libbutl/filesystem.cxx
@@ -1724,7 +1724,10 @@ namespace butl
     // we will keep trying to move the file for a second.
     //
     // The thinking is that there can be some Windows process analyzing newly
-    // created files and so preventing their move or removal.
+    // created files and so preventing their move, removal, or change.
+    //
+    // Note that we address this issue in a similar way in try_rmfile() and
+    // fdopen().
     //
     DWORD ec;
     for (size_t i (0); i < 11; ++i)
-- 
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