From d59189b0d90d5a464f8ed7d8df7b1f0643bd8e6f Mon Sep 17 00:00:00 2001
From: Jun Wu <quark@fb.com>
Date: Tue, 23 Jun 2020 22:51:50 -0700
Subject: [PATCH] revlogindex: update outdated nodemap more aggressively

Summary:
If the nodemap file is seriously out of sync, it's harder to recover on Windows,
because nodemap mmap in other processes prevents `atomic_write`.

Use `util::path::remove_file` to remove the old mmap files and improve the
success rate of nodemap rewrites.

Reviewed By: xavierd

Differential Revision: D22168134

fbshipit-source-id: 577df978b3175eac3257794f5e5ff7522cf21871
---
 eden/scm/lib/revlogindex/Cargo.toml         |  1 +
 eden/scm/lib/revlogindex/src/revlogindex.rs | 18 +++++++++++++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/eden/scm/lib/revlogindex/Cargo.toml b/eden/scm/lib/revlogindex/Cargo.toml
index 5cf9c19e62..b61462b85e 100644
--- a/eden/scm/lib/revlogindex/Cargo.toml
+++ b/eden/scm/lib/revlogindex/Cargo.toml
@@ -11,3 +11,4 @@ indexedlog = { path = "../indexedlog" }
 minibytes = { path = "../minibytes" }
 parking_lot = "0.10"
 radixbuf = { path = "../radixbuf" }
+util = { path = "../util" }
diff --git a/eden/scm/lib/revlogindex/src/revlogindex.rs b/eden/scm/lib/revlogindex/src/revlogindex.rs
index 7d333ca1a1..de995be160 100644
--- a/eden/scm/lib/revlogindex/src/revlogindex.rs
+++ b/eden/scm/lib/revlogindex/src/revlogindex.rs
@@ -394,10 +394,9 @@ impl RevlogIndex {
         let empty_nodemap_data = Bytes::from(nodemap::empty_index_buffer());
         let nodemap_data = read_path(nodemap_path, empty_nodemap_data.clone())?;
         let changelogi_data = read_path(changelogi_path, Bytes::default())?;
-        let nodemap =
-            NodeRevMap::new(changelogi_data.into(), nodemap_data.into()).or_else(|_| {
-                // Attempt to rebuild the index automatically.
-                let changelogi_data = read_path(changelogi_path, Bytes::default())?;
+        let nodemap = NodeRevMap::new(changelogi_data.clone().into(), nodemap_data.into())
+            .or_else(|_| {
+                // Attempt to rebuild the index (in-memory) automatically.
                 NodeRevMap::new(changelogi_data.into(), empty_nodemap_data.into())
             })?;
         // 20000 is chosen as it takes a few milliseconds to build up.
@@ -409,7 +408,16 @@ impl RevlogIndex {
                 let slice =
                     unsafe { slice::from_raw_parts(buf.as_ptr() as *const u8, buf.len() * 4) };
                 // Not fatal if we cannot update the on-disk index.
-                let _ = atomic_write(nodemap_path, slice, false);
+                if atomic_write(nodemap_path, slice, false).is_err() && cfg!(windows) {
+                    // On Windows it can fail if nodemap_path is mmap-ed. Retry after deleting the file.
+                    // Note: This makes the file disappear temporarily. Another process reading the
+                    // revlog at this time might have to rebuild the nodemap. The `remove_file`
+                    // strategy should be used with care and should not be used for cases where the
+                    // file needs to be always present.
+                    if util::path::remove_file(nodemap_path).is_ok() {
+                        let _ = atomic_write(nodemap_path, slice, false);
+                    }
+                }
             }
         }
         let result = Self {