refactor(locking): Make disabling locking on NFS mounts explict

Author: ranger-ross

src/cargo/core/compiler/layout.rs

@@ -103,6 +103,7 @@
 
 use crate::core::Workspace;
 use crate::core::compiler::CompileTarget;
+use crate::util::flock::is_on_nfs_mount;
 use crate::util::{CargoResult, FileLock};
 use cargo_util::paths;
 use std::path::{Path, PathBuf};
@@ -152,17 +153,21 @@ impl Layout {
         // For now we don't do any more finer-grained locking on the artifact
         // directory, so just lock the entire thing for the duration of this
         // compile.
-        let artifact_dir_lock =
-            dest.open_rw_exclusive_create(".cargo-lock", ws.gctx(), "build directory")?;
+        let artifact_dir_lock = if is_on_nfs_mount(root.as_path_unlocked()) {
+            None
+        } else {
+            Some(dest.open_rw_exclusive_create(".cargo-lock", ws.gctx(), "artifact directory")?)
+        };
 
-        let build_dir_lock = if root != build_root {
+        let build_dir_lock = if root == build_root || is_on_nfs_mount(build_root.as_path_unlocked())
+        {
+            None
+        } else {
             Some(build_dest.open_rw_exclusive_create(
                 ".cargo-lock",
                 ws.gctx(),
                 "build directory",
             )?)
-        } else {
-            None
         };
         let root = root.into_path_unlocked();
         let build_root = build_root.into_path_unlocked();
@@ -222,7 +227,7 @@ pub struct ArtifactDirLayout {
     timings: PathBuf,
     /// The lockfile for a build (`.cargo-lock`). Will be unlocked when this
     /// struct is `drop`ped.
-    _lock: FileLock,
+    _lock: Option<FileLock>,
 }
 
 impl ArtifactDirLayout {

src/cargo/util/flock.rs

@@ -427,7 +427,7 @@ fn acquire(
 }
 
 #[cfg(all(target_os = "linux", not(target_env = "musl")))]
-fn is_on_nfs_mount(path: &Path) -> bool {
+pub fn is_on_nfs_mount(path: &Path) -> bool {
     use std::ffi::CString;
     use std::mem;
     use std::os::unix::prelude::*;
@@ -445,7 +445,7 @@ fn is_on_nfs_mount(path: &Path) -> bool {
 }
 
 #[cfg(any(not(target_os = "linux"), target_env = "musl"))]
-fn is_on_nfs_mount(_path: &Path) -> bool {
+pub fn is_on_nfs_mount(_path: &Path) -> bool {
     false
 }
 

src/cargo/util/mod.rs

@@ -42,7 +42,7 @@ mod dependency_queue;
 pub mod diagnostic_server;
 pub mod edit_distance;
 pub mod errors;
-mod flock;
+pub mod flock;
 pub mod frontmatter;
 pub mod graph;
 mod hasher;