add an optional parameter to File.rename to avoid data loss about sdk

[lrhn]

Checking first is a race condition. The only way to be certain is to have the operation fail if it is not the first to create the target file.
That will allow separate processes to all create files in the same directory, as long as they all retry with a fresh name on failure, using the file system itself as the mutex.

That does mean that the operation itself must fail atomically, not just move a non-atomic extra check into the same library function. That buys nothing.

If there is no atomic "own this file name from scratch" operation in the OS, then it's probably not going to be possible.

[lrhn]

Changing the signature of an interface method breaks existing third-party classes which implement that interface, because they no longer satisfy the interface signature of that method

[a-siva]

@a-siva if rename takes an optional parameter to avoid the overwrite, how this is creating a breaking change? if you not changing the default behavior I think there is no breaking change. Do you want to modify rename differently?

See comment above .

[mraleph]

If you are concerned about newPath existing you can just check that before executing rename. Is there any reason why you want this behavior to be baked into rename itself?

cc @brianquinlan @lrhn

[mraleph]

Good point about atomicity.

• Linux has renameat2 with RENAME_NOREPLACE (Linux 3.15, glibc 2.28)
• Mac OS X has renameatx_np with RENAME_EXCL (10.12+)
• On Windows MoveFileExW without MOVEFILE_REPLACE_EXISTING should also error

Both Linux and Mac OS X require underlying file system to support atomic replacement (not all file systems do).

[stephane-archer]

@mraleph can the requirement of the underlying file system be an issue?
Can it be detected and an exception be thrown in that case?

[a-siva]

This is going to be a breaking change and would require updates in a number of packages that override File operations.

[stephane-archer]

@a-siva if rename takes an optional parameter to avoid the overwrite, how this is creating a breaking change?
if you not changing the default behavior I think there is no breaking change.
Do you want to modify rename differently?