If two Clojure projects are started concurrently, and both require the same :git/url dependency, then one of the projects will raise an exception. This doesn't appear to be a problem for maven dependencies. We have encountered the issue during local testing and continuous integration.
Minimal repro case:
mkdir gitlibs
mkdir project
echo '{:deps {com.cognitect/test-runner {:git/url "https://github.com/cognitect-labs/test-runner" :sha "b6b3193fcc42659d7e46ecd1884a228993441182"}}}' > project/deps.edn
export GITLIBS=gitlibs
(cd project && clojure -Spath) & (cd project && clojure -Spath)
Running this is likely to raise the following exception:
Cloning: https://github.com/cognitect-labs/test-runner
Cloning: https://github.com/cognitect-labs/test-runner
Error building classpath. Cannot lock /home/sean/tmp/project/gitlibs/_repos/github.com/cognitect-labs/test-runner/config. Ensure that no other process has an open file handle on the lock file /home/sean/tmp/project/gitlibs/_repos/github.com/cognitect-labs/test-runner/config.lock, then you may delete the lock file and retry.
org.eclipse.jgit.api.errors.JGitInternalException: Cannot lock /home/sean/tmp/project/gitlibs/_repos/github.com/cognitect-labs/test-runner/config. Ensure that no other process has an open file handle on the lock file /home/sean/tmp/project/gitlibs/_repos/github.com/cognitect-labs/test-runner/config.lock, then you may delete the lock file and retry.
at org.eclipse.jgit.api.CloneCommand.call(CloneCommand.java:206)
at org.eclipse.jgit.api.CloneCommand.call(CloneCommand.java:89)
at clojure.tools.gitlibs.impl$call_with_auth.invokeStatic(impl.clj:50)
at clojure.tools.gitlibs.impl$call_with_auth.invoke(impl.clj:41)
at clojure.tools.gitlibs.impl$git_clone_bare.invokeStatic(impl.clj:71)
at clojure.tools.gitlibs.impl$git_clone_bare.invoke(impl.clj:68)
at clojure.tools.gitlibs.impl$ensure_git_dir.invokeStatic(impl.clj:110)
at clojure.tools.gitlibs.impl$ensure_git_dir.invoke(impl.clj:100)
at clojure.tools.gitlibs$resolve.invokeStatic(gitlibs.clj:33)
at clojure.tools.gitlibs$resolve.invoke(gitlibs.clj:29)
at clojure.tools.gitlibs$procure.invokeStatic(gitlibs.clj:47)
at clojure.tools.gitlibs$procure.invoke(gitlibs.clj:41)
at clojure.tools.deps.alpha.extensions.git$eval966$fn__968.invoke(git.clj:41)
at clojure.lang.MultiFn.invoke(MultiFn.java:239)
at clojure.tools.deps.alpha$expand_deps.invokeStatic(alpha.clj:181)
at clojure.tools.deps.alpha$expand_deps.invoke(alpha.clj:164)
at clojure.tools.deps.alpha$resolve_deps.invokeStatic(alpha.clj:231)
at clojure.tools.deps.alpha$resolve_deps.invoke(alpha.clj:213)
at clojure.tools.deps.alpha.script.make_classpath$create_classpath.invokeStatic(make_classpath.clj:61)
at clojure.tools.deps.alpha.script.make_classpath$create_classpath.invoke(make_classpath.clj:53)
at clojure.tools.deps.alpha.script.make_classpath$run.invokeStatic(make_classpath.clj:79)
at clojure.tools.deps.alpha.script.make_classpath$run.invoke(make_classpath.clj:72)
at clojure.tools.deps.alpha.script.make_classpath$_main.invokeStatic(make_classpath.clj:118)
at clojure.tools.deps.alpha.script.make_classpath$_main.doInvoke(make_classpath.clj:93)
at clojure.lang.RestFn.applyTo(RestFn.java:137)
at clojure.lang.Var.applyTo(Var.java:705)
at clojure.core$apply.invokeStatic(core.clj:665)
at clojure.main$main_opt.invokeStatic(main.clj:514)
at clojure.main$main_opt.invoke(main.clj:510)
at clojure.main$main.invokeStatic(main.clj:664)
at clojure.main$main.doInvoke(main.clj:616)
at clojure.lang.RestFn.applyTo(RestFn.java:137)
at clojure.lang.Var.applyTo(Var.java:705)
at clojure.main.main(main.java:40)
Caused by: org.eclipse.jgit.errors.LockFailedException: Cannot lock /home/sean/tmp/project/gitlibs/_repos/github.com/cognitect-labs/test-runner/config. Ensure that no other process has an open file handle on the lock file /home/sean/tmp/project/gitlibs/_repos/github.com/cognitect-labs/test-runner/config.lock, then you may delete the lock file and retry.
at org.eclipse.jgit.storage.file.FileBasedConfig.save(FileBasedConfig.java:209)
at org.eclipse.jgit.api.CloneCommand.fetch(CloneCommand.java:294)
at org.eclipse.jgit.api.CloneCommand.call(CloneCommand.java:200)
... 33 more
I'm not sure what the best fix is. A straightforward approach would be to acquire a blocking file lock inside clojure.tools.gitlibs.impl/call-with-auth.
For example, when cloning or checking-out $GITLIBS/_repos/github.com/cognitect-labs/test-runner, clojure.tools.gitlibs could acquire a file lock on $GITLIBS/_repos/github.com/cognitect-labs/test-runner.lock.
I'm happy to propose a patch along these lines.
