OK so this is a weird one.

Once a week or so, by Jenkins builds get stuck with Waiting for next available executor on master. E.g. now, the a build got stuck for 2 days this way.

The funny thing is: I can resolve this bug simply by read-only-browsing around in the Jenkins UI. Once I view the console output of the finished build before the hanging build, the hanging build suddenly starts building.

So, "looking angry at Jenkins" makes the issue go away.

I could reproduce this 4 times so far, but it takes a week or so to happen again so it's not exactly easy to reproduce.

After short consideration if you have any idea what might cause this, please advise how I can gather more information to figure this out. Thanks!

(I've filed the bug as `core` but don't know if it might be caused by a different plugin.)

Jenkins 2.95
Plugins:

{{
org.jenkins-ci.main:jenkins-war:2.95
org.jenkins-ci:crypto-util:1.1
commons-httpclient:commons-httpclient:3.1-jenkins-1
aopalliance:aopalliance:1.0
com.google.inject:guice:4.0
org.jenkins-ci.modules:slave-installer:1.6
org.springframework:spring-dao:1.2.9
org.jenkins-ci.modules:instance-identity:2.1
org.jenkins-ci:constant-pool-scanner:1.2
org.connectbot.jbcrypt:jbcrypt:1.0.0
org.jenkins-ci.modules:ssh-cli-auth:1.4
org.ow2.asm:asm-commons:5.0.3
org.jenkins-ci:symbol-annotation:1.1
com.github.jnr:jnr-constants:0.9.8
org.jenkins-ci.modules:windows-slave-installer:1.9.2
commons-digester:commons-digester:2.1
commons-io:commons-io:2.4
org.kohsuke:trilead-putty-extension:1.2
commons-codec:commons-codec:1.9
org.kohsuke:libzfs:0.8
org.jenkins-ci.ui:jquery-detached:1.2
org.kohsuke.stapler:json-lib:2.4-jenkins-2
org.jvnet.robust-http-client:robust-http-client:1.2
org.ow2.asm:asm:5.0.3
net.java.sezpoz:sezpoz:1.12
org.kohsuke.stapler:stapler-adjunct-timeline:1.5
org.jenkins-ci:winstone:4.1
org.slf4j:log4j-over-slf4j:1.7.25
org.jenkins-ci:version-number:1.4
org.codehaus.groovy:groovy-all:2.4.11
org.jvnet.hudson:commons-jelly-tags-define:1.0.1-hudson-20071021
org.jenkins-ci:jmdns:3.4.0-jenkins-3
commons-lang:commons-lang:2.6
org.springframework:spring-jdbc:1.2.9
org.codehaus.woodstox:wstx-asl:3.2.9
org.springframework:spring-core:2.5.6.SEC03
org.springframework:spring-aop:2.5.6.SEC03
org.samba.jcifs:jcifs:1.3.17-kohsuke-1
org.jenkins-ci:bytecode-compatibility-transformer:1.8
org.kohsuke.stapler:stapler-jrebel:1.253
org.jenkins-ci.main:cli:2.95
com.sun.solaris:embedded_su4j:1.1
javax.inject:javax.inject:1
org.jenkins-ci.modules:upstart-slave-installer:1.1
org.apache.commons:commons-compress:1.10
commons-beanutils:commons-beanutils:1.8.3
org.jvnet.localizer:localizer:1.24
org.fusesource.jansi:jansi:1.11
org.springframework:spring-beans:2.5.6.SEC03
javax.xml.stream:stax-api:1.0-2
org.slf4j:slf4j-jdk14:1.7.25
org.jvnet.hudson:activation:1.1.1-hudson-1
commons-jelly:commons-jelly-tags-fmt:1.0
net.i2p.crypto:eddsa:0.2.0
jfree:jfreechart:1.0.9
org.jenkins-ci:task-reactor:1.4
org.apache.ant:ant-launcher:1.8.4
org.apache.sshd:sshd-core:1.6.0
oro:oro:2.0.8
org.jenkins-ci.main:jenkins-core:2.95
org.jenkins-ci:commons-jexl:1.1-jenkins-20111212
org.kohsuke:access-modifier-annotation:1.11
org.jenkins-ci.plugins.icon-shim:icon-set:1.0.5
stax:stax-api:1.0.1
com.google.code.findbugs:jsr305:2.0.1
org.kohsuke:windows-package-checker:1.2
org.acegisecurity:acegi-security:1.0.7
org.jenkins-ci.modules:sshd:2.3
commons-fileupload:commons-fileupload:1.3.1-jenkins-2
org.kohsuke.stapler:stapler-groovy:1.253
org.jenkins-ci.modules:launchd-slave-installer:1.2
org.jenkins-ci:annotation-indexer:1.12
org.kohsuke:libpam4j:1.8
jline:jline:2.12
com.github.jnr:jffi:1.2.15
org.kohsuke.stapler:stapler-adjunct-zeroclipboard:1.3.5-1
org.kohsuke.stapler:stapler-adjunct-codemirror:1.3
org.ow2.asm:asm-util:5.0.3
org.slf4j:jcl-over-slf4j:1.7.25
org.kohsuke:akuma:1.10
javax.mail:mail:1.4.4
org.hamcrest:hamcrest-core:1.3
jfree:jcommon:1.0.12
org.springframework:spring-context-support:2.5.6.SEC03
com.google.guava:guava:11.0.1
org.jvnet.hudson:jtidy:4aug2000r7-dev-hudson-1
org.jenkins-ci:commons-jelly:1.1-jenkins-20120928
org.jenkins-ci.ui:handlebars:1.1.1
org.springframework:spring-context:2.5.6.SEC03
org.jenkins-ci.ui:jquery-detached:1.2.1
org.ow2.asm:asm-analysis:5.0.3
io.github.stephenc.crypto:self-signed-cert-generator:1.0.0
com.github.jnr:jffi:1.2.15
org.jvnet.winp:winp:1.25
javax.servlet.jsp.jstl:javax.servlet.jsp.jstl-api:1.2.1
org.kohsuke.stapler:stapler:1.253
commons-discovery:commons-discovery:0.4
org.jenkins-ci.dom4j:dom4j:1.6.1-jenkins-4
org.jenkins-ci:memory-monitor:1.9
org.jenkins-ci.modules:systemd-slave-installer:1.1
org.jvnet.hudson:xstream:1.4.7-jenkins-1
org.jvnet:tiger-types:2.2
com.sun.xml.txw2:txw2:20110809
org.springframework:spring-web:2.5.6.SEC03
org.kohsuke.jinterop:j-interop:2.0.6-kohsuke-1
org.jenkins-ci.main:remoting:3.14
org.jruby.ext.posix:jna-posix:1.0.3-jenkins-1
com.github.jnr:jnr-ffi:2.1.4
com.github.jnr:jnr-posix:3.0.41
javax.annotation:javax.annotation-api:1.2
org.kohsuke.jinterop:j-interopdeps:2.0.6-kohsuke-1
com.infradna.tool:bridge-method-annotation:1.13
org.ow2.asm:asm-tree:5.0.3
args4j:args4j:2.0.31
org.kohsuke:asm5:5.0.1
antlr:antlr:2.7.6
relaxngDatatype:relaxngDatatype:20020414
com.jcraft:jzlib:1.1.3-kohsuke-1
org.kohsuke.stapler:stapler-jelly:1.253
org.jenkins-ci.ui:bootstrap:1.3.2
commons-collections:commons-collections:3.2.2
net.java.dev.jna:jna:4.2.1
junit:junit:4.12
org.jenkins-ci:trilead-ssh2:build-217-jenkins-11
org.slf4j:slf4j-api:1.7.25
net.sf.ezmorph:ezmorph:1.0.6
org.apache.ant:ant:1.8.4
org.springframework:spring-webmvc:2.5.6.SEC03
com.github.jnr:jnr-x86asm:1.0.2
xpp3:xpp3:1.1.4c
jaxen:jaxen:1.1-beta-11
commons-jelly:commons-jelly-tags-xml:1.1
}}