Gradle Spawn Plugin

A plugin for the Gradle build system that allows spawning, detaching and terminating processes on unix systems.

Usage

Applying the plugin

To use the Spawn plugin, include the following in your build script:

plugins {
    id 'ch.kk7.spawn'
}

Tasks

The plugin introduces two task types to your gradle build, but doesn't add any explicit tasks itself.

Spawn Task

The Spawn Task will bring a given command in a running state and put it into background. If configured correctly, it will not spawn a second instance but can still determine if the previously running instance died. A simple setup looks like:

task ping(type: SpawnTask) {
    command "ping localhost"
}

Spawn Task extends the Kill Task, since it might need to kill before launching a new process in case its configuration changed. A full example:

task processStarted(type: SpawnTask) {
    // mandatory command to be spawned
    // alternative: command "commandToRun with arguments"
    commandLine "commandToRun", "with", "arguments"
    
    // special environment variables for the new process
    environment ENV_KEY: "ENV_VALUE"
    
    // regular expression to await on the processes stdout/stderr before assuming it is successfully started
    // this let's you block the task until a service is ready and put it in background at this point
    waitFor "Listening on port [0-9]+"
    
    // maximum wait time in milliseconds for the `waitFor` expression to match
    waitForTimeout 30000
    
    // Alternate location of PID (and instance) files
    pidFile "${buildDir}/spawn/${name}.pid"
    
    workingDir "another/process/base/dir"
    
    // milliseconds before killing the process the hard way (kill -9)
    killTimeout 5000
    
    // recommended way of killing the process if the PID was lost (like `killall` or `pkill`). 
    // Try to avoid sideffects as `killall java` might not be a good idea.
    killallCommandLine "pkill", "-f", "somebinary .* arg2"
    killallCommandLine "bash", "-c", "kill -9 \$(lsof -t -i:8080 -sTCP:LISTEN)"
    
    // stdout and stderr are redirected into this file
    stdOutFile "${pidFile}.out"
    
    // use standard gradle inputs to let it fail the up-to-date checks
    // which triggers a kill+relaunch of the process
    inputs.file = "src/main/resources/config.properties"
}
// test.dependsOn processStarted

Starting a process performs the following steps:

if no PID file exists, no matching process is running or any input changed → not up-to-date
if not up-to-date: kill running processes (see KillTask)
start a new process and listen on stdout/stderr until the waitFor expression matches

Kill Task

Whereas the SpawnTask will (kill and) launch a process, the KillTask will only remove it. Usefull as part of a cleanup step. A subset of the methods of the spawn task are supported.

task processStopped(type: SpawnTask) {
    // inherits properties from a given SpawnTask
    kills mySpawnTask
    
    // alternatively use the previously explained...
    pidFile
    killTimeout
    killallCommandLine
}
// test.finalizedBy processStopped

Killing a process performs the following steps:

if the pid file exists: kill $pid
if the pid file exists after $killTimeoutms elapsed: kill -9 $pid and remove the pid file
if killallCommandLine is defined, run it

Limitations

The plugin requires the native kill command on the system and access to the hidden pid filed of the JVM (Oracle or OpenJDK).