From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 07 Apr 2010 05:21:12 GMT
Subject: Re: [PATCH v2] Make xmalloc and xrealloc thread-safe
Message-ID: <7vk4sjg7nb.fsf@alter.siamese.dyndns.org>
In-Reply-To: <20100407031655.GA7156@spearce.org>

"Shawn O. Pearce" <spearce@spearce.org> writes:

>> +static void try_to_free_from_threads(size_t size)
>> +{
>> +	int self = pthread_equal(read_mutex_owner, pthread_self());
>> +	if (!self)
>> +		read_lock();
>> +	release_pack_memory(size, -1);
>> +	if (!self)
>> +		read_unlock();
>> +}
>
> Is there any concern that a partially unset read_mutex_owner might
> look like the current thread's identity?
>
> That is, memset() can be setting the bytes one by one.  If the lock
> is being released we might observe the current owner as ourselves
> if we see only part of that release, and our identity is the same
> as another thread, only with the lower-address bytes unset.

Yuck.  I hope that it doesn't mean we need another mutex to protect the
owner data.