add a suffix to a new cache files in case of failure of renaming it t…

…o an exisiting cache file already in use (#48137)

* add a suffix to a new cache files in case of failure of renaming it to an exisiting file

base/loading.jl

@@ -927,6 +927,8 @@ function find_all_in_cache_path(pkg::PkgId)
 end
 
 ocachefile_from_cachefile(cachefile) = string(chopsuffix(cachefile, ".ji"), ".", Base.Libc.dlext)
+cachefile_from_ocachefile(cachefile) = string(chopsuffix(cachefile, ".$(Base.Libc.dlext)"), ".ji")
+
 
 # use an Int counter so that nested @time_imports calls all remain open
 const TIMING_IMPORTS = Threads.Atomic{Int}(0)
@@ -2091,7 +2093,6 @@ function compilecache(pkg::PkgId, path::String, internal_stderr::IO = stderr, in
             if pkg.uuid !== nothing
                 entrypath, entryfile = cache_file_entry(pkg)
                 cachefiles = filter!(x -> startswith(x, entryfile * "_") && endswith(x, ".ji"), readdir(cachepath))
-
                 if length(cachefiles) >= MAX_NUM_PRECOMPILE_FILES[]
                     idx = findmin(mtime.(joinpath.(cachepath, cachefiles)))[2]
                     evicted_cachefile = joinpath(cachepath, cachefiles[idx])
@@ -2104,11 +2105,31 @@ function compilecache(pkg::PkgId, path::String, internal_stderr::IO = stderr, in
                 end
             end
 
-            # this is atomic according to POSIX (not Win32):
-            rename(tmppath, cachefile; force=true)
             if cache_objects
-                rename(tmppath_so, ocachefile::String; force=true)
+                try
+                    rename(tmppath_so, ocachefile::String; force=true)
+                catch e
+                    e isa IOError || rethrow()
+                    isfile(ocachefile) || rethrow()
+                    # Windows prevents renaming a file that is in use so if there is a Julia session started
+                    # with a package image loaded, we cannot rename that file.
+                    # The code belows append a `_i` to the name of the cache file where `i` is the smallest number such that
+                    # that cache file does not exist.
+                    ocachename, ocacheext = splitext(ocachefile)
+                    old_cachefiles = Set(readdir(cachepath))
+                    num = 1
+                    while true
+                        ocachefile = ocachename * "_$num" * ocacheext
+                        in(basename(ocachefile), old_cachefiles) || break
+                        num += 1
+                    end
+                    # TODO: Risk for a race here if some other process grabs this name before us
+                    cachefile = cachefile_from_ocachefile(ocachefile)
+                    rename(tmppath_so, ocachefile::String; force=true)
+                end
             end
+            # this is atomic according to POSIX (not Win32):
+            rename(tmppath, cachefile; force=true)
             return cachefile, ocachefile
         end
     finally

test/precompile.jl

@@ -1708,6 +1708,31 @@ precompile_test_harness("BadInvalidations") do load_path
     end
 end
 
+# https://github.com/JuliaLang/julia/issues/48074
+precompile_test_harness("WindowsCacheOverwrite") do load_path
+    # https://github.com/JuliaLang/julia/pull/47184#issuecomment-1364716312
+    write(joinpath(load_path, "WindowsCacheOverwrite.jl"),
+    """
+    module WindowsCacheOverwrite
+
+    end # module
+    """)
+    ji, ofile = Base.compilecache(Base.PkgId("WindowsCacheOverwrite"))
+    (@eval (using WindowsCacheOverwrite))
+
+    write(joinpath(load_path, "WindowsCacheOverwrite.jl"),
+    """
+    module WindowsCacheOverwrite
+
+    f() = "something new"
+
+    end # module
+    """)
+
+    ji_2, ofile_2 = Base.compilecache(Base.PkgId("WindowsCacheOverwrite"))
+    @test ofile_2 == Base.ocachefile_from_cachefile(ji_2)
+end
+
 empty!(Base.DEPOT_PATH)
 append!(Base.DEPOT_PATH, original_depot_path)
 empty!(Base.LOAD_PATH)