Re: zsh got stuck without any message because of history lock file

[Mikael Magnusson <mikachu@xxxxxxxxx>]

On 26 June 2014 22:46, Mikael Magnusson <mikachu@xxxxxxxxx> wrote:
> On 25 April 2014 07:02, Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> wrote:
>> On Apr 24, 10:02am, Bart Schaefer wrote:
>> }
>> } The way the code is currently written the shell will wait until 10
>> } seconds after the modification time stamp of the file.  If for some
>> } reason the time stamp is wrong (clocks out of sync with NFS server,
>> } for example) then it may end up waiting for longer.
>>
>> So ... here is a patch that checks for future timestamps.  If it finds
>> one, it leaves errno set to EEXIST, which results in:
>>
>> zsh: locking failed for /home/schaefer/.zhistory: file exists
>>
>> This isn't perfect, but at least it provides a clue.
>>
>> There's a controversial bit in this patch:  It appears HIST_FCNTL_LOCK
>> may have been broken ever since workers/28047 in 2010.  That patch
>> changed flockhistfile() [which is misnamed, it uses fcntl] to return 0
>> on success, but then also this:
>>
>>         ret = flockhistfile(fn, keep_trying);
>>         if (ret)
>>             return ret;
>>
>> That means that we only stop when flockhistfile() FAILS.  On success,
>> we go on and lock with BOTH fcntl AND a .LOCK file.  This completely
>> contradicts the documentation claim that "this may provide better
>> performance."  So the second hunk below makes flockhistfile() the
>> only lock applied when HIST_FCNTL_LOCK is set.
>>
>> However, this would mean that every zsh that is accessing the same
>> HISTFILE has to be using the same locking options.  Is that OK?
>
> I'm not 100% sure it's because of this change, but recently, I've had
> new terminals stuck forever on startup until I exit all open terminals
> logged in as that user (or possibly just a specific one of them). It
> happens very spuriously, maybe a few times per week. I have
> histfcntllock set. On one occasion I tried moving the .history file
> instead of exiting, and this also immediately unstuck all new
> terminals.

I'm still seeing reports of this every now and then in #zsh (and I
have the option unset so I'm not sure if it happens to me anymore.) If
nobody fixed this, it's probably still a problem.

-- 
Mikael Magnusson