ConcurrentModificationException using new Startable.dependsOn(startable)

I ran into an error in one of my TravisCI builds using the new dependsOn mechanism:

    13780 ERROR 🐳 [postgres:9.6.12]  - Could not start container
    java.util.ConcurrentModificationException
    	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1660)
    	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
    	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
    	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:550)
    	at java.base/java.util.stream.AbstractPipeline.evaluateToArrayNode(AbstractPipeline.java:260)
    	at java.base/java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:517)
    	at org.testcontainers.containers.GenericContainer.applyConfiguration(GenericContainer.java:510)
    	at org.testcontainers.containers.GenericContainer.tryStart(GenericContainer.java:301)
    	at org.testcontainers.containers.GenericContainer.lambda$doStart$0(GenericContainer.java:285)
    	at org.rnorth.ducttape.unreliables.Unreliables.retryUntilSuccess(Unreliables.java:81)
    	at org.testcontainers.containers.GenericContainer.doStart(GenericContainer.java:283)
    	at org.testcontainers.containers.GenericContainer.start(GenericContainer.java:272)
    	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
    	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1654)
    	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
    	at java.base/java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:290)
    	at java.base/java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:746)
    	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
    	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
    	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
    	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
    	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)

My containers are defined like this:

	@Container
	public static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>()
					.withNetworkAliases("testpostgres")
					.withDatabaseName("testdb");
	
    @Container
    public static MicroProfileApplication<?> app = new MicroProfileApplication<>()
                    .withEnv("POSTGRES_HOSTNAME", "testpostgres")
                    .withEnv("POSTGRES_PORT", "5432")
                    .withAppContextRoot("/myservice")
                    .dependsOn(postgres);

Using the latest version of testcontainers (1.12.0), the exception lines up with this bit of code:

    private void applyConfiguration(CreateContainerCmd createCommand) {
        HostConfig hostConfig = buildHostConfig();
        createCommand.withHostConfig(hostConfig);

        // Set up exposed ports (where there are no host port bindings defined)
        ExposedPort[] portArray = exposedPorts.stream()
                .map(ExposedPort::new)
                .toArray(ExposedPort[]::new);  // << --- CONCURRENT MOD EX HERE

It should also be noted that I am starting my containers in parallel like this:

containersToStart.parallelStream().forEach(GenericContainer::start);

which should be OK, since I believe the main value of dependsOn is that it allows us to do parallel container start without needing to worry about dependencies.

Start in GenericContainer.applyConfiguration at the exposedPorts stream, then trace the dependsOn and parallel GenericContainer.start paths shown in the report. Reproduce the PostgreSQL/application setup with containersToStart.parallelStream().forEach(GenericContainer::start), and consider the issue complete when dependent containers start without ConcurrentModificationException.