Resolving Conflicts
This chapter tells you how to work in a team development environment, where multiple users who are working on the same files might need to reconcile their changes.
In settings where multiple users are working on the same set of files, conflicts can occur. Helix enables your team to work on the same files simultaneously and resolve any conflicts that arise. For example, conflicts occur if two users change the same file (the primary concern in team settings) or you edit a previous revision of a file rather than the head revision.
When you attempt to submit a file that conflicts with the head revision in the depot, Helix requires you to resolve the conflict. Merging changes from a development branch to a release branch is another typical task that requires you to resolve files.
To prevent conflicts, Helix enables you to lock files when they are edited. However, locking can restrict team development. Your team needs to choose the strategy that maximizes file availability while minimizing conflicts. For details, refer to Locking files.
You might prefer to resolve files using graphical tools like P4V, the Helix Visual Client, and its associated visual merge tool P4Merge.
How conflicts occur
File conflicts can occur when two users edit and submit two versions of the same file. Conflicts can occur in a number of ways, for example:
- Bruno opens
//depot/dev/main/jam/command.c#8
for edit. - Gale subsequently opens the same file for edit in her own client workspace.
- Bruno and Gale both edit
//depot/dev/main/jam/command.c#8
. - Bruno submits a changelist containing
//depot/dev/main/jam/command.c
, and the submit succeeds. - Gale submits a changelist with her version of
//depot/dev/main/jam/command.c
. Her submit fails.
If Helix accepts Gale’s version into the depot, her changes will overwrite Bruno’s changes. To prevent Bruno’s changes from being lost, Helix rejects the changelist and schedules the conflicting file to be resolved. If you know of file conflicts in advance and want to schedule a file for resolution, sync it. Helix detects the conflicts and schedules the file for resolution.
How to resolve conflicts
To resolve a file conflict, you determine the contents of the files you intend
to submit by issuing the p4 resolve
command and choosing the desired method
of resolution for each file. After you resolve conflicts, you submit the
changelist containing the files.
Note
If you open a file for edit, then sync a subsequently submitted revision from the depot, Helix requires you to resolve to prevent your own changes from being overwritten by the depot file.
By default, Helix uses its diff program to detect conflicts. You can configure a third-party diff program. For details, see Diffing files.
To resolve conflicts and submit your changes, perform the following steps:
- Sync the files (for example p4 sync //depot/dev/main/jam/...). Helix detects any conflicts and schedules the conflicting files for resolve.
- Issue the
p4 resolve
command and resolve any conflicts. See Options for resolving conflicts for details about resolve options. - Test the resulting files (for example, compile code and verify that it runs).
- Submit the changelist containing the files.
Note
If any of the three file revisions participating in the merge are binary instead
of text, a three-way merge is not possible. Instead, p4 resolve
performs a
two-way merge: the two conflicting file versions are presented, and you can
choose between them or edit the one in your workspace before submitting the
changelist.
Your, theirs, base and merge files
The p4 resolve
command uses the following terms during the merge process:
File revision | Description |
---|---|
yours |
The revision of the file in your client workspace, containing changes you made. |
theirs |
The revision in the depot, edited by another user, that |
base |
The file revision in the depot that yours and theirs were edited from (the closest common ancestor file). |
merge |
The file generated by Helix from theirs, yours, and base. |
result |
The final file resulting from the resolve process. |
Options for resolving conflicts
To specify how a conflict is to be resolved, you issue the p4 resolve
command, which displays a dialog for each file scheduled for resolve. The dialog
describes the differences between the file you changed and the conflicting
revision. For example:
C:\bruno_ws> p4 resolve //depot/dev/main/jam/command.c
c:\bruno_ws\dev\main\jam\command.c - merging //depot/dev/main/jam/command.c#9
Diff chunks: 4 yours + 2 theirs + 1 both + 1 conflicting
Accept(a) Edit(e) Diff(d) Merge (m) Skip(s) Help(?) e:
The differences between each pair of files are summarized by p4 resolve
.
Groups of lines (chunks) in the yours
, theirs
, and base
files can differ
in various ways. Chunks can be:
- Diffs: different between two of the three files: yours, theirs, or base
- Conflicts: different in all three files
In the preceding example:
- Four chunks are identical in theirs and base but are different in yours.
- Two chunks are identical in yours and base but are different in theirs.
- One chunk was changed identically in yours and theirs.
- One chunk is different in yours, theirs, and base.
Helix’s recommended choice is displayed at the end of the command line. Pressing Enter or choosing performs the recommended choice.
You can resolve conflicts in three basic ways:
- Accept a file without changing it (see Accepting yours, theirs, or merge)
- Edit the merge file with a text editor (see Editing the merge file)
- Merge changes selectively using a merge program (see Merging to resolve conflicts)
The preceding options are interactive. You can also specify resolve options on
the p4 resolve
command line, if you know which file you want to accept. For
details, see Resolve command-line options. To re-resolve a resolved but unsubmitted file,
specify the -f
option when you issue the p4 resolve
command. You cannot
re-resolve a file after you submit it. The following sections describe the
resolve options in more detail:
Accepting yours, theirs, or merge
To accept a file without changing it, specify one of the following options:
Option | Description | Remarks |
---|---|---|
|
Accept recommended file |
|
|
Accept edit |
If you edited the merge file (by selecting |
|
Accept merge |
Accept merge into the client workspace as the resolved revision. The version in the client workspace is overwritten. |
|
Accept theirs |
Accept theirs into the client workspace as the resolved revision. The version in the client workspace is overwritten. |
|
Accept yours |
Accept yours into the client workspace as the resolved revision, ignoring changes that might have been made in theirs. |
Accepting yours, theirs, edit, or merge overwrites changes, and the generated merge file might not be precisely what you want to submit to the depot. The most precise way to ensure that you submit only the desired changes is to use a merge program or edit the merge file.
Editing the merge file
To resolve files by editing the merge file, choose the e
option. Helix
launches your default text editor, displaying the merge file. In the merge file,
diffs and conflicts appear in the following format:
>>>> ORIGINALfile
#n
(text from the original version)
==== THEIRfile
#m
(text from their file)
==== YOURSfile
(text from your file)
<<<<
To locate conflicts and differences, look for the difference marker >>>>
and
edit that portion of the text. Examine the changes made to theirs to make sure
that they are compatible with your changes. Make sure you remove all conflict
markers before saving. After you make the desired changes, save the file. At the
p4 resolve
prompt, choose ae
.
By default, only the conflicts between the yours and theirs files are
marked. To generate difference markers for all differences, specify the -v
option when you issue the p4 resolve
command.
Merging to resolve conflicts
A merge program displays the differences between yours, theirs, and the base
file, and enables you to select and edit changes to produce the desired result
file. To configure a merge program, set P4MERGE
to the desired program. To
use the merge program during a resolve, choose the m
option. For details about
using a specific merge program, consult its online help.
After you merge, save your results and exit the merge program. At the p4
resolve
prompt, choose am
.
Full list of resolve options
The p4 resolve
command offers the following options:
Option | Action | Remarks |
---|---|---|
|
Help |
Display help for |
|
Accept automatically |
Accept the auto-selected file:
|
|
Accept edit |
If you edited the merge file (by selecting |
|
Accept merge |
Accept merge into the client workspace as the resolved revision. The version in the client workspace is overwritten. |
|
Accept theirs |
Accept theirs into the client workspace as the resolved revision. The version in the client workspace is overwritten. |
|
Accept yours |
Accept yours into the client workspace as the resolved revision, ignoring changes that might have been made in theirs. |
|
Diff |
Show diffs between merge and yours. |
|
Diff merge |
Show diffs between merge and base. |
|
Diff theirs |
Show diffs between theirs and base. |
|
Diff yours |
Show diffs between yours and base. |
|
Edit merged |
Edit the preliminary merge file generated by Helix. |
|
Edit theirs |
Edit the revision in the depot that the client revision conflicts with (usually the head revision). This edit is read-only. |
|
Edit yours |
Edit the revision of the file currently in the workspace. |
|
Merge |
Invoke the command |
|
Skip |
Skip this file and leave it scheduled for resolve. |
Note
The merge file is generated by the Helix service, but the differences
displayed by dy
, dt
, dm
, and d
are generated by your workstation’s diff
program. To configure another diff program to be launched when you choose a d
option during a resolve, set P4DIFF
. For more details, see Diffing files.
Example 28. Resolving file conflicts
To resolve conflicts between his work on a Jam README
file and Earl’s work on
the same file, Bruno types p4 resolve //depot/dev/main/jam/README
and sees
the following:
Diff chunks: 0 yours + 0 theirs + 0 both + 1 conflicting Accept(a) Edit(e) Diff(d) Merge (m) Skip(s) Help(?) e: e
Bruno sees that he and Earl have made a conflicting change to the file. He types
e
to edit the merge file and searches for the difference marker >>>>
. The
following text is displayed:
Jam/MR (formerly "jam - make(1) redux") /+\ >>>> ORIGINAL README#26 +\ Copyright 1993, 1997 Christopher Seiwald. ==== THEIRS README#27 +\ Copyright 1993, 1997, 2004 Christopher Seiwald. ==== YOURS README +\ Copyright 1993, 1997, 2005 Christopher Seiwald. <<<< \+/
Bruno and Earl have updated the copyright date differently. Bruno edits the
merge file so that the header is correct, exits from the editor and types am
.
The edited merge file is written to the client workspace, and he proceeds to
resolve the next file.
When a version of the file is accepted during a resolve, the file in the workspace is overwritten, and the new client file must still be submitted to the depot. New conflicts can occur if new versions of a file are submitted after you resolve but before you submit the resolved files. This problem can be prevented by locking the file before you perform the resolve. For details, see Locking files.
Resolving Branched Files, Deletions, Moves and Filetype Changes
Beyond reconciling changes to the contents of related files after integration, you can also determine how other kinds of changes are handled. For example:
- You edit
header.cc
in the mainline while a coworker deletes it in the release branch (or vice versa). You integrate fixes in the release branch back to main. During resolve, you can decide whetherheader.cc
is deleted from the mainline or the action in the release branch is ignored, preservingheader.cc
in the mainline. - A developer implements RCS keywords in source files in a development branch,
and changes their Helix filetype from
text
totext+k
. The release manager wants to integrate new features from the development branch to the mainline, but does not want to enable keyword expansion in the mainline. During resolve, the release manager can choose to ignore the filetype change. - The file
header.cc
is branched frommain
torel
. Subsequently, it’s renamed toheaderx.cc
in main, and moved in the release branch to theheaders
subfolder.
Following are simple cases describing how you can resolve non-content changes to
related files. After a source file is branched to a target file, changes are
made as describe below, then you integrate the source to the target. To choose
the outcome, you specify the resolve options at
(“Accept Theirs”) or ay
(“Accept Yours”) as follows:
- The source is edited and target is deleted: the
at
option re-adds the source in the target branch. Theay
option causes the file to remain deleted in the target branch. - The source is deleted and the target is edited: the
at
option causes the file to be deleted in the target branch. Theay
option retains the edited content in the target branch. - The target file was moved after being branched: the
at
option moves the target file to the source file name and location. Theay
option retains the target file name and location. - The filetype of the source file was changed after it was branched: the
at
option propagates the change to the target. Theay
option leaves the filetype of the target unchanged. If the differing filetypes do not conflict, you have the option of combining them. -
Files have been moved or renamed in conflicting ways: you are prompted to choose a path and filename. Example:
Resolving move to //depot/rel/headerx.cc Filename resolve: at: //depot/rel/headerx.cc ay: //depot/rel/headers/header.cc am: //depot/rel/headers/headerx.cc
By default, the p4 resolve
command resolves all types of change, content and
non-content. To constrain the type of actions that you want to resolve, specify
the -A
option as follows:
Option | What is Resolved |
---|---|
|
Resolve attributes set by |
|
Integrations where the source is edited and the target is deleted. |
|
Resolve file content changes as well as actions. |
|
Integrations where the source is deleted and target is edited. |
|
Renames and moves. |
|
Filetype changes. |
|
Charset changes. |
To perform more than one type of resolve, combine the options (for example:
-Abd
). By default, resolving is performed file by file, interactively. To
specify the same outcome for a particular action (for example, propagate all
moves), and avoid the prompting, include the desired option on the command line.
For example: p4 resolve -Am -at
Resolve command-line options
The p4 resolve
options described below enable you to resolve directly
instead of interactively. When you specify one of these options in the p4
resolve
command, files are resolved as described in the following table:
Option | Description |
---|---|
|
Accept the auto-selected file. |
|
Accept yours. |
|
Accept theirs. Use this option with caution, because the file revision in your client workspace is overwritten with the head revision from the depot, and you cannot recover your changes. |
|
Accept the recommended file revision according to the following logic:
|
|
Accept the recommended file revision, even if conflicts remain. If this option is used, edit the resulting file in the workspace to remove any difference markers. |
|
Accept the recommended file revision according to the following logic:
|
Example 29. Automatically accepting particular revisions of conflicting files
Bruno has been editing the documentation files in /doc
and knows that some
of them require resolving. He types p4 sync
doc/*.guide, and all of these files that conflict with files in the
depot are scheduled for resolve.
He then types p4 resolve -am
and the merge files for all scheduled resolves
are generated, and those merge files that contain no line set conflicts are
written to his client workspace. He’ll still need to manually resolve any
conflicting files, but the amount of work he needs to do is substantially
reduced.
Resolve reporting commands
The following reporting commands are helpful when you are resolving file conflicts:
Command | Meaning |
---|---|
|
Diffs the file revision in the workspace with the last revision you synced, to display changes you have made. |
|
Diffs two depot files. The specified files can be any two file revisions and different files. When you diff depot files, Helix service uses its own diff program, not the diff
program configured by setting |
|
Previews the specified sync, listing which files have conflicts and need to be resolved. |
|
Reports files that have been resolved but not yet submitted. |
Locking files
After you open a file, you can lock it to prevent other users from submitting it before you do. The benefit of locking a file is that conflicts are prevented, but when you lock a file, you might prevent other team members from proceeding with their work on that file.
Preventing multiple resolves by locking files
Without file locking, there is no guarantee that the resolve process ever ends. The following scenario demonstrates the problem:
- Bruno opens file for edit.
- Gale opens the same file in her client for edit.
- Bruno and Gale both edit their client workspace versions of the file.
- Bruno submits a changelist containing that file, and his submit succeeds.
- Gale submits a changelist with her version of the file; her submit fails because of file conflicts with the new depot’s file.
- Gale starts a resolve.
- Bruno edits and submits a new version of the same file.
-
Gale finishes the resolve and attempts to submit; the submit fails and must now be merged with Bruno’s latest file.
…and so on.
To prevent such problems, you can lock files, as follows.
- Before scheduling a resolve, lock the file.
- Sync the file (to schedule a resolve).
- Resolve the file.
- Submit the file.
- Helix automatically unlocks the file after successful changelist submission.
To list open locked files on UNIX, issue the following command:
$ p4 opened | grep "*locked*"
Preventing multiple checkouts
To ensure that only one user at a time can work on the file, use the +l
(exclusive-open) file type modifier. For example:
$ p4 reopen -t binary+l file
Although exclusive locking prevents concurrent development, for some file types (binary files), merging and resolving are not meaningful, so you can prevent conflicts by preventing multiple users from working on the file simultaneously.
Your Helix administrator can use the p4 typemap
command to ensure that all
files of a specified type (for instance, //depot/.../*.gif
for all .gif
files) can only be opened by one user at a time. See the P4 Command Reference.
The difference between p4 lock
and +l
is that p4 lock
allows anyone to
open a file for edit, but only the person who locked the file can submit it. By
contrast, a file of type +l
prevents more than one user from opening the file.