[Vm-dev] Re: [squeak-dev] FileDoesNotExistException on existing changes file during trunk update

Eliot Miranda eliot.miranda at gmail.com
Tue Sep 2 15:03:58 UTC 2014

Hi Bert,

On Mon, Sep 1, 2014 at 7:13 AM, Bert Freudenberg <bert at freudenbergs.de>

> On 01.09.2014, at 15:56, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> >> Another thought is that given the abundance of memory these days, we
> might cache both sources and changes in main memory (which would also speed
> up full-text searches).
> >
> > Pharo is planning to eliminate them altogether which is more coherent
> than caching them.
> That's another discussion, but it might be a step towards that.
> >  But IMO the solution is easy, maintain a *single* read-only copy of the
> sources and changes files in SourceFilesArray (or whatever the class is
> called; I'm on my phone) and read source through them instead of reopen ing
> the damn things all the time.
> Except that Squeak files do not maintain an independent file position
> pointer, so reading from different positions in the same file is not
> thread-safe. That's why the file is opened again.

Can you explain more.  I don't understand.  As I see it every file instance
has its own FILE structure so I don't understand how this can be so.  Files
are derived from FilePlugin's primitiveFileOpen function.  That is
implemented in terms of fileOpenNamesizewritesecure, which allocates a
ByteArray to hold state (so no two Smalltalk files share state) and then
uses sqFileOpen to open the underlying file and fill in the state.  The C
library implementation of sqFileOpen in
platforms/Cross/plugins/FilePlugin/sqFilePluginBasicPrims.c uses fopen et
al, again creating unique state.  So I don't see how having a writable
Smalltalk file and a separate read-only Smalltalk file on the sources and
changes can result in other than two separate independent file pointers.

There *is* an issue with the structure of file access in the debugger.  If
one were to step through execution of accessing source from e.g. the
read-only sources file then the very act of fetching sources for the
methods being displayed would confuse the state in the file one was
observing through the debugger.  But that's hardly a new situation (one can
get into a similar situation with the current setup), and the debugger
could ease the situation by wrapping source access with something that
reset the file's buffer etc.

> > Then the file's own buffers will provide done caching.  Annoying that I
> write this code in 2008 for newspeak but we still rely on the mad "run the
> GC to finalize files when open fails" approach.
> Well, you writing this for newspeak does not immediately benefit Squeak.
> But if you point us to the code maybe someone can port it to Squeak?

I already did a year or two ago and it got shot down on the debugger
grounds I reiterated above.

> - Bert -

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