ElectricAccelerator job statuses, or, what the heck is a skipped job?

If you’ve ever looked at an annotation file generated by Electric Make, you may have noticed the status attribute on jobs. In this article I’ll explain what that attribute means so that you can better understand the performance and behavior of your builds.

Annotation files and the status attribute

An annotation file is an XML-enhanced version of the build log, optionally produced by Electric Make as it executes a build. In addition to the regular log content, annotation includes details like the duration of each job and the dependencies between jobs. the status attribute is one of several attributes on the <job> tag:

<job id="J00007fba40004240"  status="conflict" thread="7fba4a7fc700" type="rule" name="a" file="Makefile" line="6" neededby="J00007fba400042e0">
<conflict type="file" writejob="J00007fba400041f0" file="/home/ericm/src/a" rerunby="J0000000002a27890"/>
<timing invoked="0.512722" completed="3.545985" node="ericm15-2"/>
</job>

The status attribute may have one of five values:

  • normal
  • reverted
  • skipped
  • conflict
  • rerun

Let’s look at the meaning of each in detail.

normal jobs

Normal jobs are just that: completely normal. Normal jobs ran as expected and were later found to be free of conflicts, so their outputs and filesystem modifications were incorporated into the final build result. Note that normal is the default status, so it’s usually not explicitly specified in the annotation. That is, if a job does not have a status attribute, its status is normal. If you run the following makefile with emake, you’ll see the all job has normal status:

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all: ; @echo done

Here’s the annotation for the normal job:

<job id="Jf3502098" thread="f46feb40" type="rule" name="all" file="Makefile" line="1">
<command line="1">
<argv>echo done</argv>
<output src="prog">done
</output>
</command>
<timing weight="0" invoked="0.333677" completed="0.343138" node="chester-1"/>
</job>

reverted and skipped jobs

Reverted and skipped jobs are two sides of the same coin. In both cases, emake has determined that running the job is unnecessary, either because of an error in a serially earlier job, or because a prerequisite of the job was itself reverted or skipped. Remember, emake’s goal is to produce output that is identical to a serial GNU make build. In that context, barring the use of –keep-going or similar features, jobs following an error would not be run, so to preserve compatibility with that baseline, emake must not run those jobs either — or at least emake must appear not to have run those jobs.

That brings us to the sole difference between reverted and skipped jobs. Reverted jobs had already been executed (or had at least started) at the point when emake discovered the error that would have caused them not to run. Any output produced by a reverted job is discarded, so it has no effect on the final output of the build. In contrast, skipped jobs had not yet been started when the error was discovered. Since the job had not yet run, there is not output to discard.

Running the following simple makefile with at least two agents should produce one reverted job, b, and one skipped job, c.

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all: a b c
a: ; @sleep 2 && exit 1
b: ; @sleep 2
c: b ; @echo done

Here’s the annotation for the reverted and skipped jobs:

<job id="Jf3502290"  status="reverted" thread="f3efdb40" type="rule" name="b" file="Makefile" line="5" neededby="Jf35022f0">
<timing weight="0" invoked="0.545836" completed="2.558411" node="chester-1"/>
</job>
<job id="Jf35022c0"  status="skipped" thread="0" type="rule" name="c" file="Makefile" line="7" neededby="Jf35022f0">
<timing weight="0" invoked="0.000000" completed="0.000000" node=""/>
</job>

conflict jobs

A job has conflict status if emake detected a conflict in the job: the job ran too early, and used a different version of a file than it would have had it run in the correct serial order. Any output produced by the job is discarded, since it is probably incorrect, and a rerun job is created to replace the conflict job. The following simple makefile will produce a conflict job if run without an emake history file, and with at least two agents:

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all: a b
a: ; @sleep 2 && echo hello > a
b: ; @cat a

Here’s the annotation for the conflict job:

<job id="Jf33021d0"  status="conflict" thread="f44ffb40" type="rule" name="b" file="Makefile" line="5" neededby="Jf3302200">
<conflict type="file" writejob="Jf33021a0" file="/home/ericm/blog/melski.net/job_status/tmp/a" rerunby="J09b1b3c8"/>
<timing weight="0" invoked="0.541597" completed="0.552053" node="chester-2"/>
</job>

rerun jobs

A rerun job is created to replace a conflict job, rerunning the commands from the original conflict job but with a corrected filesystem context, to ensure the job produces the correct result. There are a few key things to keep in mind when you’re looking at rerun jobs:

  • By design, rerun jobs are executed after any serially earlier jobs have been verified conflict-free and committed to disk. That’s a consequence of the way that emake detects conflicts: each job is checked, in strict serial order, and committed only if it has not conflict. If a job has a conflict it is discarded as described above, and a rerun job is created to redo the work of that job.
  • It is impossible for a rerun job to have a conflict, since it is guaranteed not to run until all preceeding jobs have finished. In fact, emake does not even bother to check for conflicts on rerun jobs.
  • Rerun jobs are executed immediately upon being created, and while the rerun job is running emake will not start any other jobs. Any jobs that were already running when the rerun started are allowed to finish, but new jobs must wait until the rerun completes. Although this impairs performance in some cases, this conservation strategy helps to avoid chains of conflicts that would be even more detrimental to performance. Of course you typically won’t see conflicts and reruns if you run your build with a good history file, so in practice the performance impact of rerun jobs is immaterial.

The following simple makefile will produce a rerun job, if run without a history file and using at least two agents (yes, this is the same makefile that we used to demonstrate a conflict job!):

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all: a b
a: ; @sleep 2 && echo hello > a
b: ; @cat a

And here’s the annotation fragment for the rerun job:

<job id="J09b1b3c8"  status="rerun" thread="f3cfeb40" type="rule" name="b" file="Makefile" line="5" neededby="Jf3302200">
<command line="5">
<argv>cat a</argv>
<output src="prog">hello
</output>
</command>
<timing weight="0" invoked="2.283755" completed="2.293563" node="chester-1"/>
</job>

Job status in ElectricAccelerator annotation

To the uninitiated, ElectricAccelerator job status types might seem cryptic and mysterious, but as you’ve now seen, there’s really not much to it. I hope you’ve found this article informative. As always, if you have any questions or suggestions, hit the comments below. And don’t forget to checkout Ask Electric Cloud if you are looking for help with Electric Cloud tools!

#pragma multi and rules with multiple outputs in GNU make

Recently we released ElectricAccelerator 6.2, which introduced a new bit of makefile syntax — #pragma multi — which allows you to indicate that a single rule produces multiple outputs. Although this is a relatively minor enhancement, I’m really excited about it because this it represents a new direction for emake development: instead of waiting for the GNU make project to add syntactic features and then following some time later with our emulation, we’re adding features that GNU make doesn’t have — and hopefully they will have to follow us for a change!

Unfortunately I haven’t done a good job articulating the value of #pragma multi. Unless you’re a pretty hardcore makefile developer, you probably look at this and think, “So what?” So let’s take a look at the problem that #pragma multi solves, and why #pragma multi matters.

Rules with multiple outputs in GNU make

The problem we set out to solve is simply stated: how can you specify to GNU make that one rule produces two or more output files? The obvious — but wrong — answer is the following:

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foo bar: baz
touch foo bar

Unfortunately, this fragment is interpreted by GNU make as declaring two rules, one for foo and one for bar — it just so happens that the command for each rule creates both files. That will do more-or-less the right thing if you run a from-scratch, serial build:

$ gmake foo bar
touch foo bar
gmake: `bar' is up to date.

By the time GNU make goes to update bar, it’s already up-to-date thanks to the execution of the rule for foo. But look what happens when you run this same build in parallel:

$ gmake -j 2 foo bar
touch foo bar
touch foo bar

Oops! — the files were updated twice. No big deal in this trivial example, but it’s not hard to imagine a build where running the commands to update a file twice would produce bogus output, particularly if those updates could be happening simultaneously.

So what’s a makefile developer to do? In standard GNU make syntax, there’s only one truly correct way to create a rule with multiple outputs: pattern rules:

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%.x %.y: %.in
touch $*.x $*.y

In contrast with explicit rules, GNU make interprets this fragment as declaring a single rule that produces two output files. Sounds perfect, but there’s a significant limitation to this solution: all of the output files must share a common sequence in the filenames (called the stem in GNU make parlance). That is, if your rule produces foo.x and foo.y, then pattern rules will work for you because the outputs both have foo in their names.

If your output files do not adhere to that naming limitation, then pattern rules can’t help you. In that case, you’re pretty much out of luck: there is no way to correctly indicate to GNU make that a single rule produces multiple output files. There are a variety of hacks you can try to coerce GNU make to behave properly, but each has its own limitations. The most common is to nominate one of the targets as the “primary”, and declare that the others depend on that target:

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bar: foo
foo: baz
touch foo bar

Watch what happens when you run this build serially from scratch:

$ gmake foo bar
touch foo bar
gmake: Nothing to be done for `bar'.

Not bad, other than the odd “nothing to be done” message. At least the files weren’t generated twice. How about running it in parallel, from scratch?

$ gmake -j 2 foo bar
touch foo bar
gmake: Nothing to be done for `bar'.

Awesome! We still have the odd “nothing to be done” message, but just as in the serial build, the command was only invoked one time. Problem solved? Nope. What happens in an incremental build? If you’re lucky, GNU make happens to do the right thing and regenerate the files. But in one incremental build scenario, GNU make utterly fails to do the right thing. Check out what happens if the secondary output is deleted, but the primary is not:

$ rm -f bar && gmake foo bar
gmake: `foo' is up to date.
gmake: Nothing to be done for `bar'.

That’s right: GNU make failed to regenerate bar. If you’re very familiar with the build system, you might realize what had happened and think to either delete foo as well, or touch baz so that foo appears out-of-date (which would cause the next run to regenerate both outputs). But more likely at this point you just throw your hands up and do a full clean rebuild.

Note that all of the alternatives in vanilla GNU make have similar deficiencies. This kind of nonsense is why incremental builds have a bad reputation. This is why we created #pragma multi.

Rules with multiple outputs in Electric Make

By default Electric Make emulates GNU make, so it inherits all of GNU make’s limitations regarding rules with multiple outputs — with one critical exception. Even when running a build in parallel, Electric Make ensures that the output matches that produced by a serial GNU make build, which means that even the original, naive attempt will “work” for full builds regardless of whether the build is serial (single agent) or parallel (multiple agents).

Given that foundation, why did we bother with #pragma multi? There are a couple reasons:

  1. Correct incremental builds: with #pragma multi you can correctly articulate the relationships between inputs and outputs and thus ensure that all the outputs get rebuilt in incremental builds, rather than using kludges and hoping for the best.
  2. Out-of-the-box performance: although Electric Make guarantees correct output of the build, if you don’t have an up-to-date history file for the build you may waste time and compute resources running commands that don’t need to be run (work that will eventually be discarded when Electric Make detects the error). In the examples shown here the cost is negligible, but in real builds it could be significant.

Using #pragma multi is easy: just add the directive before the rule that will generate multiple outputs:

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#pragma multi
foo bar: baz
touch foo bar

Watch what happens when this makefile is executed with Electric Make:

$ emake foo bar
touch foo bar

Note that there is no odd “is up to date” or “nothing to be done” message for bar — because Electric Make understands that both outputs are created by a single rule. Let’s verify that the build works as desired in the tricky incremental case that foiled GNU make — deleting bar without deleting foo:

$ rm -f bar && emake foo bar
touch foo bar

As expected, both outputs are regenerated: even though foo existed, bar did not, so the commands were executed.

Summary: rules with multiple outputs

Let’s do a quick review of the strategies for creating rules with multiple outputs. For simplicity we can group them into three categories:

  • #pragma multi
  • The naive approach, which does not actually create a single rule with multiple outputs at all.
  • Any of the various hacks for approximating rules with multiple outputs.

Here’s how each strategy fares across a variety of build modes:

Electric Make GNU make
Full (serial) Full (parallel) Incremental Full (serial) Full (parallel) Incremental
#pragma multi N/A
Naive
Hacks


The table paints a grim picture for GNU make: there is no way to implement rules with multiple outputs using standard GNU make which reliably gives both correct results and good performance across all types of builds. The naive approach generates the output files correctly in serial builds, but may fail in parallel builds. The various hacks work for full builds, but may fail in incremental builds. Even in cases where the output files are generated correctly, the build is marred by spurious “is up to date” or “nothing to be done for” messages — which is why most of the entries in the GNU make side are yellow rather than green.

In contrast, #pragma multi allows you to correctly generate multiple outputs from a single rule, for both full and incremental builds, in serial and in parallel. The naive approach also “works” with Electric Make, in that it will produce correct output files, but like GNU make the build is cluttered with spurious warnings. And, unless you have a good history file, the naive approach can trigger conflicts which may negatively impact build performance. Finally, despite its sophisticated conflict detection and correction smarts, even Electric Make cannot ensure correct incremental builds when you’ve implemented one of the multiple output hacks.

So there you have it. This is why we created #pragma multi: without it, there’s just no way to get the job done quickly and reliably. You should give ElectricAccelerator a try.

try_eade_button2

Fixing recursive make

Recursive make is one of those things that everybody loves to hate. It’s even been the subject of one of those tired “… Considered Harmful” diatribes. According to popular opinion, recursive make will sap performance from your build, make it nigh impossible to ensure correctness in parallel builds, and may render the user sterile. OK, maybe not that last one. But seriously, the arguments against recursive make are legion, and deeply entrenched. The problem? They’re flawed. That’s because they assume there’s only one way to implement recursive make — when the submake is invoked, the parent make is blocked until the submake completes. That’s how almost everybody does it. But in Electric Make, part of ElectricAccelerator, we developed a novel new approach called non-blocking recursive make. This design eliminates the biggest problems attributed to recursive make, without requiring a painful and costly conversion of your build system to non-recursive make.

The problem with traditional recursive make

There’s really just two problems at the heart of complaints with traditional recursive make: first, there’s no way to ensure correctness of a parallel recursive make based build without overserializing the submakes, because there’s no way to articulate dependencies between individual targets in different submakes. That means you can’t have a dependency graph that is both correct and precise. Instead you either leave out the critical dependency entirely, which makes parallel (ie, fast) builds unreliable; or you serialize submakes in their entirety, which shackles build performance because no part of a submake with even a single dependency on some portion of an earlier submake can begin until the entire ealier submake completes. Second, even if there were a way to specify precise dependencies between targets in different submakes, most versions of make have implemented recursive make such that the parent make is blocked from proceeding until the submake has completed. Consider a typical use of recursive make with implicit serializations between submakes:

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all:
@for dir in util client server ; do \
$(MAKE) -C $$dir; \
done

Each submake compiles a bunch of source files, then links them together into a library (util) or an executable (client and server). The only actual dependency between the work in the three make instances is that the client and server programs need the util library. Everything else is parallelizable, but with traditional recursive make, gmake is unable to exploit that parallelism: all of the work in the util submake must finish before any part of the client submake begins!

Conflict detection and non-blocking recursive make

If you’re familiar with Electric Make, you already know how it solves the first half of the recursive make problem: conflict detection and correction. I’ve written about conflict detection before, but here’s a quick recap: using the explicit dependencies given in the makefiles and information about the files accessed as each target is built, emake is able to dynamically determine when targets have been built too early due to missing explicit dependencies, and rerun those targets to generate the correct output. Electric Make can ensure the correctness of parallel builds even in the face of incomplete dependencies, even if the missing dependencies are between targets in different submakes. That means you need not serialize entire submakes to ensure the build will run correctly in parallel.

Like an acrobat’s safety net, conflict detection allows us to consider solutions to the other half of the problem that would otherwise be considered risky, if not outright madness. In fact, our solution would not be possible without conflict detection: non-blocking recursive make. This is analogous to the difference between blocking and non-blocking I/O: rather than waiting for a recursive make to finish, emake carries on executing subsequent commands in the build immediately, including other recursive makes. Conflict detection ensures that only the commands in each submake which require serialization are executed sequentially, so the build runs as quickly as possible, but the final build output is identical to a serial build.

The impact of this change is dramatic. Here I’ve plotted the execution of the simple build defined above on four cores, using both gmake (normal recursive make) and emake (non-blocking recursive make):

Recursive make build with gmake


Recursive make build with emake

Electric Make is able to execute this build about 20% faster than gmake, with no changes to the Makefiles or the execution environment. emake is literally able to squeeze more parallelism out of recursive-make-based builds than gmake. In fact, we can precisely quantify just how much more parallelism emake gets through an application of Amdahl’s law. First, we compute the best possible speedup for the build — that’s just the serial runtime divided by the best possible parallel runtime, which we can figure out through analysis of the depedency graph and runtime of individual jobs in the build (the Longest Serial Chain report in ElectricInsight can do this for you). Then we can compute the parallelizable portion P of the build by plugging the speedup S into this equation: P = 1 – (1 / S). Here’s how that works out for gmake and emake:

gmake emake
Serial baseline 65s 65s
Best build time 13.5s 7.5s
Best speedup 4.8x 8.7x
Parallel portion 79% 89%

On this build, non-blocking recursive make increases the parallel portion of the build by 10%. That may not seem like much, but Amdahl’s law shows how dramatically that difference affects the speedup you can expect as you apply more cores:

Implementation

On the backend, non-blocking recursive make is handled by conflict detection — the jobs from the recursive make are checked for conflicts in the serial order defined by the makefile structure. Any issues caused by aggressively running recursive makes early are detected during the conflict check, and the target that ran too early is rerun to generate the correct result.

On the frontend, emake uses a strategy that is at once both brilliant in its simplicity, and diabolical in its trickery. It starts with an environment variable. When emake is invoked recursively, it checks the value of EMAKE_BUILD_MODE. If it is set to node, emake runs in so-called stub mode: rather than executing the submake (parsing the makefile and building targets), emake captures the invocation context (working directory, command-line and environment) in a file on disk, prints a “magic” string and exits with a zero status code.

The file containing the invocation context is identified by a second environment variable, ECLOUD_RECURSIVE_COMMAND_FILE. The Accelerator agent (which handles invoking commands on behalf of emake) checks for the presence of that file after every command that is run. If it is found, the agent relays the content to the toplevel emake invocation, where a new make instance is created to represent the submake invocation. That instance comes with it’s own parse job of course, which gets inserted into the queue of jobs. Some (short) time later, the parse job will run, discover whatever work must be run by the submake, and create additional rule jobs.

The magic string — EMAKE_FNORD — serves as a placeholder in the stdout stream for the jobs, so emake can figure out which portion of the output text comes before and which portion comes after the submake. This ensures that the build output log is identical to that generated by a serialized gmake build. For example, given the following rule that invokes a submake, you’d expect to see the “Before” and “After” messages printed before and after the output generated by commands in the submake itself:

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all:
@echo Before util ; \
@$(MAKE) -C util ; \
@echo After util

With non-blocking recursive make, the submake has not actually executed when the “echo After util” command runs. If emake doesn’t account for that reordering, both the “Before” and “After” messages will appear before any of the output from the submake. EMAKE_FNORD allows emake to “stitch” the output together so the build log matches a serial log.

Limitations

Conflict detection and non-blocking recursive make together solve the main problems associated with recursive make. But there are a couple scenarios where non-blocking recursive make does not work well. Fortunately, these are uncommon in practice and easily addressed.

Capturing recursive make stdout

The first scenario is when the build captures the output of the recursive make invocation, rather than letting it print to stdout as normal. Since emake defers the execution of the submake and prints only EMAKE_FNORD to stdout, this will not work. There are two reasons you might do this: first, you might want to have separate build logs for each submake, to simplify error detection and management. In this situation, the simplest workaround is to remove the redirection and instead us emake’s annotated build log, an XML version of the build output log which can be easily processed using standard tools. Second, you may be using make as a text-processing tool (sort of a “poor man’s” Perl), rather than for building per se:

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all:
@$(MAKE) -f genlist.mk > objects.txt
@cat objects.txt | xargs rm

In this case, the workaround is to explicitly force emake to run in so-called “local” mode, which means emake will handle the recursive make invocation as a blocking invocation, just like traditional make would. You can force emake into local mode by adding EMAKE_BUILD_MODE=local to the environment before the recursive make invocation.

Immediate consumption of build products

The second scenario is when the build consumes the product of the submake in the same command that contains the invocation. For example:

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all:
@$(MAKE) -C sub foo && cp sub/foo ./foo

Here the build assumes that the output files generated by the submake will be available for use immediately after the submake completes. Obviously this is not the case with non-blocking recursive make — when the invocation of $(MAKE) -C sub foo completes, only the submake stub has actually finished. The build products will not be available until after the submake is actually processed later. Note that in this build both the recursive make invocation and the commands that use the build products from that invocation are treated as a single command from the perspective of make: make actually invokes the shell, and the shell then runs the recursive make and cp commands.

The workaround is simple: split the consumer into a distinct command, from the perspective of make:

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all:
@$(MAKE) -C sub foo
@cp sub/foo ./foo

With that trivial change, emake is able to treat the cp as a continuation job, which can be serialized against the completion of the recursive make as needed.

A fix for recursive make

For years, people have heaped scorn and criticism on recursive make. They’ve nearly convinced everybody that even considering its use is automatically wrong — you probably can’t help feeling a little bit guilty when you use recursive make. But the reality is that recursive make is a reasonable way to structure a large build. You just need a better make. With conflict detection and non-blocking recursive make, Electric Make has fixed the problems usually associated with recursive make, so you can get parallel builds that are both fast and correct. Give it a try!

Another confusing conflict in ElectricAccelerator

After solving the case of the confounding conflict, my user came back with another scenario where ElectricAccelerator produced an unexpected (to him) conflict:

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all:
@$(MAKE) foo
@cp foo bar
foo:
@sleep 2 && echo hello world > foo

If you run this build without a history file, using at least two agents, you will see a conflict on the continuation job that executes the cp foo bar command, because that job is allowed to run before the job that creates foo in the recursive make invocation. After one run of course, emake records the dependency in history, so later builds don’t make the same mistake.

This situation is a bit different from the symlink conflict I showed you previously. In that case, it was not obvious what caused the usage that triggered the conflict (the GNU make stat cache). In this case, it’s readily apparent: the continuation job reads (or attempts to read) foo before foo has been created. That’s pretty much a text-book example of the sort of thing that causes conflicts.

What’s surprising in this example is that the continuation job is not automatically serialized with the recursive make that precedes it. In a very real sense, a continuation job is an artificial construct that we created for bookkeeping reasons internal to the implementation of emake. Logically we know that the commands in the continuation job should follow the commands in the recursive make. In fact it would be absolutely trivial for emake to just go ahead and stick in a dependency to ensure that the continuation is not allowed to start until after the recursive make finishes, thereby avoiding this conflict even when you have no history file.

Given a choice between two strategies that both produce correct output, emake uses the strategy that produces the best performance in the general case.

Absolutely trivial to do, yes — but also absolutely wrong. Not for correctness reasons, this time, but for performance. Remember, emake is all about maximizing performance across a broad range of builds. Given a choice between two strategies that both produce correct output, emake uses the strategy that produces the best performance in the general case. For continuation jobs, that means not automatically serializing the continuation against the preceding recursive make. I could give you a wordy, theoretical explanation, but it’s easier to just show you. Suppose that your makefile looked like this instead of the original — the difference here is that the continuation job itself launches another recursive make, rather than just doing a simple cp:

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all:
@$(MAKE) foo
@$(MAKE) bar
foo:
@sleep 2 && echo hello world > foo
bar:
@sleep 2 && echo goodbye > bar

Hopefully you agree that the ideal execution of this build would have both foo and bar running in parallel. Forcing the continuation job to be serialized with the preceding recursive make would choke the performance of this build. And just in case you’re thinking that emake could be really clever by looking at the commands to be executed in the continuation job, and only serializing “when it needs to”: it can’t. First, that would require emake to implement an entire shell syntax parser (or several, really, since you can override SHELL in your makefile). Second, even if emake had that ability, it would be thwarted the instant the command is something like my_custom_script.pl — there’s no way to tell what will happen when that gets invoked. It could be a simple filesystem access. It could be a recursive make. It could be a whole series of recursive makes. Even when the command is something you think you recognize, can emake really be sure? Maybe cp is not our trustworthy standard Unix cp, but something else entirely.

Again, all is not lost for this user. If you want to avoid this conflict, you have a couple options:

  1. Use a good history file from a previous build. This is the simplest solution. You’ll only get conflicts in this build if you run without a history file.
  2. Refactor the makefile. You can explicitly describe the dependency between the commands in the continuation job and the recursive make by refactoring the makefile so that the stuff in the continuation is instead its own target, thus taking the decision out of emake’s hands. Here’s one way to do that:
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    all: do_foo
    @cp foo bar
    do_foo:
    @$(MAKE) foo
    foo:
    @sleep 2 && echo hello world > foo

Either of these will eliminate the conflict from your build.

LEGO “Ship It!” Awards

Scriptics Connect 1.1 "Ship It!" Award

What am I supposed to do with this?


When we wrapped up the ElectricAccelerator 6.0 release recently, I wanted to give my teammates something to commemorate the release. Traditionally these are called “Ship It!” awards, and they often take the form of a Lucite plaque or trophy, or even a physical copy of the product (on DVD or CD, for example) locked inside an acrylic block. I’ve gotten a couple of those over the years, and honestly I think they’re kind of a waste. The last one I got went on a shelf to collect dust for a few years before being relocated to the trash heap, which is a shame because those things are expensive. Really expensive. I can’t even imagine the cost of the monster awards that Microsoft gives out.

So I don’t really like the usual embodiment of the “Ship It” award, but I do really like the underlying idea. After all, shipping a software release is a significant accomplishment, the culmination of months or even years of effort by a team of smart individuals. And unlike many other human endeavors, there’s nothing tangible when you’re finished — no bridge spanning the bay nor tower reaching to the heavens. Having something to commemorate the accomplishment seems fitting, and it’s another small way that I can show my appreciation for everybody’s contributions.

The Ideal “Ship It!” Award

To me, the ideal “Ship It!” award has the following attributes:

  • Themeable: I wanted something I could customize for each release, while maintaining consistency across releases. I plan to make this a tradition.
  • Inexpensive: I wanted something I could bankroll myself, so I could retain complete creative control.
  • Compact: I wanted something that wouldn’t take up much space, so it would be portable and easy to display.
  • Geek appeal: I wanted something that my teammates would think is cool. Chunks of Lucite just don’t cut it.

LEGO “Ship It!” Awards

LEGO race car driver minifig

The winner!


After a few days of idle brainstorming and bouncing ideas off my manager and co-conspirator, I had what seemed like a great idea: LEGO minifigs. I could get a bunch of a specific LEGO minifig and give one to each person on the team. It fit all my criteria. There have been over 4,000 different minifigs released since 1978, according to The Cult of LEGO. In the last two years alone LEGO has release five minifig packs, each with 16 completely new figures, so I can count on having a unique character for every feature release for the next several years. Minifigs are cheap, too — the majority can be bought for as little as a couple dollars each on Amazon or ebay. They’re obviously small. And of course, minifigs are dripping with geek appeal. What techie doesn’t like LEGO?

There was just one small problem. Minifigs are a little bit too small. There’s nowhere to put the information that would identify what it represented — the product name, release version and date, and so on. A couple more days of brainstorming gave me the solution: custom baseball cards. There are several companies that will print custom baseball cards. These outfits are obviously intended for children’s sports teams, but they will happily print cards with whatever graphic you want. You just have to create images of the front and back of your card and upload to their website. And like the minifigs themselves, the cards are inexpensive, at about $1 per card.

The ElectricAccelerator 6.0 “Ship It!” Award

For the ElectricAccelerator 6.0 “Ship It!” Award, I chose the race car driver shown above (because Accelerator is all about performance, of course!). I bought the minifigs on ebay. I spent a couple hours designing the card, then ordered them from CustomSportsProducts.com. The front shows the minifig, the product name, version, and release date, and the major new features; the back lists the names of everybody on the team. Total cost for awards for the entire team was about $40 for materials — about the cost of just one traditional Lucite-based “Ship It” award.

I was a little nervous when I presented the awards to my team a couple weeks ago, but as it turns out I needn’t have been! The reception was overwhelmingly positive. Although I hadn’t explicitly planned it this way, the minifigs actually arrived unassembled, in individual pouches. Immediately upon getting theirs, each person dumped out the pieces and started assembly — it was practically instinctive! Several people commented out loud that the award was “Awesome!” or “Really cool,” and, of course, “Kinda nerdy, but cool!” With that kind of reaction, you can bet that I’m already planning for the next release.

And finally, here’s a picture of the ElectricAccelerator 6.0 “Ship It!” Award, as it is proudly displayed on my desk:

ElectricAccelerator 6.0 "Ship It!" Award

Who doesn't love LEGO?

What’s new in ElectricAccelerator 6.0

Last week Electric Cloud announced the release of ElectricAccelerator 6.0. The most exciting development in this version is the addition of ElectricAccelerator Developer Edition, which enables users to leverage the rapidly increasing horsepower on their multicore workstations to accelerate their builds, as well as the cluster agents we’ve always supported. Even better, Developer Edition allows you to use emake to accelerate builds even when disconnected from the network, with all of the benefits you’ve come to depend on: reliable parallel builds, accurate incrementals — all that good stuff.

But there’s much more to Accelerator 6.0 than just Developer Edition. Several improvements make this the most robust, secure and easy-to-use release ever. Here are the major new features:

Electrify command-line interface overhaul

electrify is the alternate front-end to the Accelerator cluster that enables users to accelerate non-make-based builds (like SCons and JAM) as well as general purpose cluster parallel computing tasks. Accelerator 5.0 was the first release to include electrify, but that version was relatively unpolished — a minimal viable product strategy that we hoped would allow us to prove the technology in the field and provide feedback to guide the technical direction of electrify over subsequent releases. As a result of that feedback we made significant improvements to both the functionality and performance of electrify in the 5.2 and 5.4 releases, but electrify still retained the “charm” of its original clumsy user interface. At long last, we’ve taken the first big step towards addressing that in 6.0, which incorporates a significantly streamlined electrify interface. I won’t bother showing the “old clunky way” here — if you’ve been using electrify you already know, and if you haven’t, I’d rather you never see it. But I’m very pleased to show you how easy it is to accelerate a SCons build with electrify in Accelerator 6.0:

electrify --emake-cm=eacm --electrify-remote=gcc:ld scons -j 8

There are still a few warts, but then, if we fixed everything what would people complain about?

Kerberos authentication

For environments with heightened security requirements, Accelerator 6.0 supports Kerberos authentication. This improvement ensures the identity of the individual running emake and the agents that participate in the build. That means that emake can be certain that any agents it connects to are legimiate agents, rather than trojans set up to capture potentially sensitive information from emake. At the same time, it means that the agents can be certain of the authenticity of the connection from emake, so malicious users cannot spoof the connection to the agent.

Note that at this time Accelerator only provides authentication of the connction between emake and an agent. It does not encrypt traffic once the connection is established.

Submake usage reporting

One thing that occassionally causes trouble for people switching to emake is the so-called submake stub problem. The issue arises when a build uses constructs like this:

foo.a:
	$(MAKE) -C sub foo.a && cp sub/foo.a ./foo.a

With emake, the recursive make invocation is not processed inline, as you might normally expect. Instead, to maximize parallel performance across all the recursive makes in the build, a make stub captures the invocation context, relays it to the top-level emake for incorporation into the overall build graph, and exits immediately. Because the cp call is part of the same command, it runs immediately after the stub, but since none of the work of the submake has actully executed yet, the cp will fail.

Correcting this requires a trivial makefile change. Instead of chaining the recursive make and the cp together in a single command, this rule can be rewritten to explicitly use two distinct commands. With this minor adjustment, emake is able to treat the cp as a separate job that logically occurs after the work in the recursive make:

foo.a:
	$(MAKE) -C sub foo.a
	cp sub/foo.a ./foo.a

Although it’s generally straightforward to remedy the problem, it’s not always easy to determine that a build has run into a submake stub problem. Thus in Accelerator 6.0 we added a feature that will make it easier to identify these situations: if you enable file- or lookup-level annotation detail, emake will record an explicit submake usage operation in the job that invoked the recursive make, so you can tell exactly when the submake occurs relative to other file usage in the job. In the example above, the usage log for the job will contain something like this:

<op type="submake" file="/home/ericm/build/sub"/>
<op type="lookup" file="/home/ericm/build/sub/foo.a" found="0"/>

The presence of file usage after the submake operation is a warning flag that the job may have a submake stub vulnerability.

Optionally enable directory read conflicts

Another long-standing thorn-in-the-side for users switching to emake is builds that depend on strict accuracy of directory listing operations. Briefly, although emake can ensure that directory listings are 100% correct throughout the build, for performance reasons emake deliberately ignores the directory read conflicts that would provide that assurance. For a thorough explanation of the problem and the rational for that design decision, see my previous post on Exceptions to conflict detection in ElectricMake. For now, suffice to say that Accelerator 6.0 includes a new command-line option that forces emake to honor directory read conflicts: –emake-readdir-conflicts=1.

Agent log rotation

Last, but certainly not least, after only 10 years Accelerator finally incorporates a feature that’s been standard on Unix operating systems probably since the dawn of the epoch: the Accelerator agent now monitors the size of its debug log, and automatically rolls over to a new logfile when the log gets too big. That’s sure to be welcome news to anybody that’s had to enable agent debug logging while working with our support team.

Looking forward

As you can see, there’s a lot of great improvements in Accelerator 6.0. As always, I’m tremendously proud of the effort my engineering team has put into the product. Of course, a product like Accelerator is never really done. We’re already working on the next release. Stay tuned for updates on what we’re doing next.

Accelerator 6.0 is available immediately for current customers — contact support@electric-cloud.com for details. New users contact sales@electric-cloud.com.

2011 Customer Summit “Conflicts” Handout

As promised, here’s the corrected handout to accompany the presentation I gave at the 2011 Electric Cloud Customer Summit, “Conflict Detection in ElectricMake”. This content is also available as a pair of blog articles:

  1. How ElectricMake guarantees reliable parallel builds
  2. Exceptions to conflict detection in ElectricMake

Thanks to everybody who came to the talk! I really enjoyed giving it and answering your questions. Looking forward to seeing you next year!