Random SE79:04: Concurrence issues and memory leaks
Some 79:04 errors can happen randomly when the printer is being heavily used. However, it’s
impossible to find a single set of conditions that reproduce the problem. It just happens from time to
time, without a defined pattern.
These random 79:04 can have two different types of root causes:
• Memory leaks: Before a program is executed, it allocates the memory it will need. After the execution
is complete, the allocated memory is freed to be used by other programs. If the allocation or the release
of the memory are not properly programmed, every time the program is executed some memory will be
incorrectly labeled (either as used or as free). This is known as a memory leak. When a program with a
memory leak is executed a lot, the memory becomes progressively full (since it is not properly freed).
When the leak becomes too big, the printer is left ‘out of memory’ to execute new processes and a
79:04 is triggered.
• Concurrence issues: There are certain resources that can be accessed by multiple programs or by
multiple executions of the same program (what is known as multiple threads). Access to these resources
must be correctly controlled to prevent unexpected behavior. Issues caused by an incorrect control of
these resources are concurrence issues.
In the following you have a simple example: let’s imagine that there is a counter that controls the
communication between the Jetdirect card and the printer’s firmware. Whenever a new packet of
information is sent by the Jetdirect card to the printer, the counter increases. When the printer receives
the packet and processes it correctly, the counter decreases. Another process checks the counter from
time to time to see its value and take conclusions from it. If the counter is near 0, it means that the
printer is processing correctly, and if it grows too big, it may mean that there is a bottleneck somewhere
and maybe the Jetdirect card throughput is decreased to control its speed to the printer. However, if the
access to this counter is not properly controlled, undesirable effects may happen: in a real environment,
a Jetdirect card processes thousands of information packets per second, so this counter is updated
frequently, both by the Jetdirect and the printer. If at a certain point the Jetdirect and the printer try to
access the counter at the same time and the code is not prepare to handle this, it may happen that the
Jetdirect cannot increase the counter because the printer is writing to it, and what’s worse, that it does
not realize this fact. If this happens a few times each second, it may happen that the counter is
decreasing faster than it’s increasing and that at a certain point it has a negative value. And then, what
will the process that is checking this counter do? Most likely, the process will not be prepared to react to
a negative value and will launch an exception that will trigger a 79:04 system error.
Cause Solution
This type of 79:04 always occurs in heavy load conditions, so
the symptoms will always be similar to this pattern:
●
A printer that is being heavily used (printing a project or
in a reprographics environment) produces 79:04 errors
randomly, forcing the user to restart.
●
After restarting, the printer can be used without any
issues for an extended period of time, but if the workload
is consistently high, a random error will occur again.
●
The error can never be associated with a specific file.
The file that was being printed when the error occurred
the last time can be printed without issues after restart.
And a file that has been printed without issues several
times can trigger the error in the future.
●
This error is very dependant of the workflow the customer
has. The most common user workflows have been
extensively tested both by HP and by our beta sites, so it
is highly unlikely to see random 79:04 issues in these
cases. These random issues tend to occur in very specific
corner cases, and cannot be reproduced unless the exact
conditions of the workflow are replicated. They normally
happen when sending files generated by external
applications (RIPs, 3
rd
party drivers, etc.).
Random 79:04 errors are, by far, the most complex ones to
diagnose and to fix. The only solutions available in these
cases are:
1. Identify the root cause (either in the files or in the
firmware) and fix it in the code, which requires the
intervention of the GBU
2. Test any options available to modify the customer’s
workflow and see if any combination of them solves the
issue
In both cases, a profound understanding of the customer’s
workflow is necessary. In particular, the information that is
needed is:
●
Printer front panel settings
●
Application that is being used; RIP or driver that is being
used
●
Application/RIP/Driver settings
●
Type of output files this application, RIP or driver is
generating
●
Some sample files that are representative of what the
customer is using
●
Operating System
●
Method of connection to the printer
●
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