fix null gpuSlots in LocalTaskHandler

docs/reference/config.md

@@ -642,6 +642,12 @@ The following settings are available:
 `executor.exitReadTimeout`
 : Determines how long to wait before returning an error status when a process is terminated but the `.exitcode` file does not exist or is empty (default: `270 sec`). Used only by grid executors.
 
+`executor.gpus`
+: :::{versionadded} 25.04.0
+  :::
+: *Used only by the `local` executor.*
+: The maximum number of NVIDIA GPUs made available by the underlying system. When this setting is enabled, each local task is assigned GPUs based on their `accelerator` request, using the `CUDA_VISIBLE_DEVICES` environment variable.
+
 `executor.jobName`
 : Determines the name of jobs submitted to the underlying cluster executor e.g. `executor.jobName = { "$task.name - $task.hash" }`. Make sure the resulting job name matches the validation constraints of the underlying batch scheduler.
 : This setting is supported by the following executors: Bridge, Condor, Flux, HyperQueue, Lsf, Moab, Nqsii, Oar, PBS, PBS Pro, SGE, SLURM and Google Batch.

modules/nextflow/src/main/groovy/nextflow/executor/local/LocalTaskHandler.groovy

@@ -80,6 +80,8 @@ class LocalTaskHandler extends TaskHandler implements FusionAwareTask {
 
     private volatile TaskResult result
 
+    List<Integer> gpuSlots
+
     LocalTaskHandler(TaskRun task, LocalExecutor executor) {
         super(task)
         // create the task handler
@@ -142,11 +144,13 @@ class LocalTaskHandler extends TaskHandler implements FusionAwareTask {
         final workDir = task.workDir.toFile()
         final logFile = new File(workDir, TaskRun.CMD_LOG)
 
-        return new ProcessBuilder()
+        final pb = new ProcessBuilder()
                 .redirectErrorStream(true)
                 .redirectOutput(logFile)
                 .directory(workDir)
                 .command(cmd)
+        applyGpuSlots(pb)
+        return pb
     }
 
     protected ProcessBuilder fusionProcessBuilder() {
@@ -162,10 +166,18 @@ class LocalTaskHandler extends TaskHandler implements FusionAwareTask {
 
         final logPath = Files.createTempFile('nf-task','.log')
 
-        return new ProcessBuilder()
+        final pb = new ProcessBuilder()
                 .redirectErrorStream(true)
                 .redirectOutput(logPath.toFile())
                 .command(List.of('sh','-c', cmd))
+        applyGpuSlots(pb)
+        return pb
+    }
+
+    protected void applyGpuSlots(ProcessBuilder pb) {
+        if( !gpuSlots )
+            return
+        pb.environment().put('CUDA_VISIBLE_DEVICES', gpuSlots.join(','))
     }
 
     protected ProcessBuilder createLaunchProcessBuilder() {

modules/nextflow/src/main/groovy/nextflow/processor/LocalPollingMonitor.groovy

@@ -23,8 +23,10 @@ import groovy.transform.PackageScope
 import groovy.util.logging.Slf4j
 import nextflow.Session
 import nextflow.exception.ProcessUnrecoverableException
+import nextflow.executor.local.LocalTaskHandler
 import nextflow.util.Duration
 import nextflow.util.MemoryUnit
+import nextflow.util.TrackingSemaphore
 
 /**
  * Task polling monitor specialized for local execution. It manages tasks scheduling
@@ -58,6 +60,16 @@ class LocalPollingMonitor extends TaskPollingMonitor {
      */
     private final long maxMemory
 
+    /**
+     * Number of `free` GPUs available to execute pending tasks
+     */
+    private TrackingSemaphore availGpus
+
+    /**
+     * Total number of CPUs available in the system
+     */
+    private final int maxGpus
+
     /**
      * Create the task polling monitor with the provided named parameters object.
      * <p>
@@ -74,6 +86,8 @@ class LocalPollingMonitor extends TaskPollingMonitor {
         super(params)
         this.availCpus = maxCpus = params.cpus as int
         this.availMemory = maxMemory = params.memory as long
+        this.maxGpus = params.gpus as int
+        this.availGpus = new TrackingSemaphore(maxGpus)
         assert availCpus>0, "Local avail `cpus` attribute cannot be zero"
         assert availMemory>0, "Local avail `memory` attribute cannot zero"
     }
@@ -98,14 +112,16 @@ class LocalPollingMonitor extends TaskPollingMonitor {
 
         final int cpus = configCpus(session,name)
         final long memory = configMem(session,name)
+        final int gpus = configGpus(session,name)
         final int size = session.getQueueSize(name, OS.getAvailableProcessors())
 
-        log.debug "Creating local task monitor for executor '$name' > cpus=$cpus; memory=${new MemoryUnit(memory)}; capacity=$size; pollInterval=$pollInterval; dumpInterval=$dumpInterval"
+        log.debug "Creating local task monitor for executor '$name' > cpus=$cpus; memory=${new MemoryUnit(memory)}; gpus=$gpus; capacity=$size; pollInterval=$pollInterval; dumpInterval=$dumpInterval"
 
         new LocalPollingMonitor(
                 name: name,
                 cpus: cpus,
                 memory: memory,
+                gpus: gpus,
                 session: session,
                 capacity: size,
                 pollInterval: pollInterval,
@@ -128,6 +144,11 @@ class LocalPollingMonitor extends TaskPollingMonitor {
         (session.getExecConfigProp(name, 'memory', OS.getTotalPhysicalMemorySize()) as MemoryUnit).toBytes()
     }
 
+    @PackageScope
+    static int configGpus(Session session, String name) {
+        return session.getExecConfigProp(name, 'gpus', 0) as int
+    }
+
     /**
      * @param handler
      *      A {@link TaskHandler} instance
@@ -149,6 +170,16 @@ class LocalPollingMonitor extends TaskPollingMonitor {
         handler.task.getConfig()?.getMemory()?.toBytes() ?: 1L
     }
 
+    /**
+     * @param handler
+     *      A {@link TaskHandler} instance
+     * @return
+     *      The number of gpus requested to execute the specified task
+     */
+    private static int gpus(TaskHandler handler) {
+        handler.task.getConfig()?.getAccelerator()?.getRequest() ?: 0
+    }
+
     /**
      * Determines if a task can be submitted for execution checking if the resources required
      * (cpus and memory) match the amount of avail resource
@@ -174,9 +205,14 @@ class LocalPollingMonitor extends TaskPollingMonitor {
         if( taskMemory>maxMemory)
             throw new ProcessUnrecoverableException("Process requirement exceeds available memory -- req: ${new MemoryUnit(taskMemory)}; avail: ${new MemoryUnit(maxMemory)}")
 
-        final result = super.canSubmit(handler) && taskCpus <= availCpus && taskMemory <= availMemory
+        final taskGpus = gpus(handler)
+        if( taskGpus>maxGpus )
+            throw new ProcessUnrecoverableException("Process requirement exceeds available GPUs -- req: $taskGpus; avail: $maxGpus")
+
+        final availGpus0 = availGpus.availablePermits()
+        final result = super.canSubmit(handler) && taskCpus <= availCpus && taskMemory <= availMemory && taskGpus <= availGpus0
         if( !result && log.isTraceEnabled( ) ) {
-            log.trace "Task `${handler.task.name}` cannot be scheduled -- taskCpus: $taskCpus <= availCpus: $availCpus && taskMemory: ${new MemoryUnit(taskMemory)} <= availMemory: ${new MemoryUnit(availMemory)}"
+            log.trace "Task `${handler.task.name}` cannot be scheduled -- taskCpus: $taskCpus <= availCpus: $availCpus && taskMemory: ${new MemoryUnit(taskMemory)} <= availMemory: ${new MemoryUnit(availMemory)} && taskGpus: $taskGpus <= availGpus: ${availGpus0}"
         }
         return result
     }
@@ -189,6 +225,10 @@ class LocalPollingMonitor extends TaskPollingMonitor {
      */
     @Override
     protected void submit(TaskHandler handler) {
+        final taskGpus = gpus(handler)
+        if ( taskGpus > 0 ) {
+            ((LocalTaskHandler) handler).gpuSlots = availGpus.acquire(taskGpus)
+        }
         super.submit(handler)
         availCpus -= cpus(handler)
         availMemory -= mem(handler)
@@ -204,11 +244,13 @@ class LocalPollingMonitor extends TaskPollingMonitor {
      *      {@code true} when the task is successfully removed from polling queue,
      *      {@code false} otherwise
      */
+    @Override
     protected boolean remove(TaskHandler handler) {
         final result = super.remove(handler)
         if( result ) {
             availCpus += cpus(handler)
             availMemory += mem(handler)
+            availGpus.release(((LocalTaskHandler) handler).gpuSlots ?: Collections.<Integer>emptyList())
         }
         return result
     }

modules/nextflow/src/main/groovy/nextflow/util/TrackingSemaphore.groovy

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2013-2024, Seqera Labs
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package nextflow.util
+
+import java.util.concurrent.Semaphore
+
+import groovy.transform.CompileStatic
+
+/**
+ * Specialized semaphore that keeps track of which slots
+ * are being used.
+ *
+ * @author Ben Sherman <bentshermann@gmail.com>
+ */
+@CompileStatic
+class TrackingSemaphore {
+    private final Semaphore semaphore
+    private final Map<Integer,Boolean> availIds
+
+    TrackingSemaphore(int permits) {
+        semaphore = new Semaphore(permits)
+        availIds = new HashMap<>(permits)
+        for( int i=0; i<permits; i++ )
+            availIds.put(i, true)
+    }
+
+    int availablePermits() {
+        return semaphore.availablePermits()
+    }
+
+    List<Integer> acquire(int permits) {
+        semaphore.acquire(permits)
+        final result = new ArrayList<Integer>(permits)
+        for( final entry : availIds.entrySet() ) {
+            if( entry.getValue() ) {
+                entry.setValue(false)
+                result.add(entry.getKey())
+            }
+            if( result.size() == permits )
+                break
+        }
+        return result
+    }
+
+    void release(List<Integer> ids) {
+        semaphore.release(ids.size())
+        for( id in ids )
+            availIds.put(id, true)
+    }
+
+}

modules/nextflow/src/test/groovy/nextflow/processor/LocalPollingMonitorTest.groovy

@@ -21,6 +21,7 @@ import java.lang.management.ManagementFactory
 import com.sun.management.OperatingSystemMXBean
 import nextflow.Session
 import nextflow.exception.ProcessUnrecoverableException
+import nextflow.executor.local.LocalTaskHandler
 import nextflow.util.MemoryUnit
 import spock.lang.Specification
 /**
@@ -38,14 +39,15 @@ class LocalPollingMonitorTest extends Specification {
                 cpus: 10,
                 capacity: 20,
                 memory: _20_GB,
+                gpus: 0,
                 session: session,
                 name: 'local',
                 pollInterval: 100
         )
 
         def task = new TaskRun()
         task.config = new TaskConfig(cpus: 3, memory: MemoryUnit.of('2GB'))
-        def handler = Mock(TaskHandler)
+        def handler = Mock(LocalTaskHandler)
         handler.getTask() >> { task }
 
         expect:
@@ -86,14 +88,15 @@ class LocalPollingMonitorTest extends Specification {
                 cpus: 10,
                 capacity: 10,
                 memory: _20_GB,
+                gpus: 0,
                 session: session,
                 name: 'local',
                 pollInterval: 100
         )
 
         def task = new TaskRun()
         task.config = new TaskConfig(cpus: 4, memory: MemoryUnit.of('8GB'))
-        def handler = Mock(TaskHandler)
+        def handler = Mock(LocalTaskHandler)
         handler.getTask() >> { task }
         handler.canForkProcess() >> true
         handler.isReady() >> true
@@ -132,14 +135,15 @@ class LocalPollingMonitorTest extends Specification {
                 cpus: 1,
                 capacity: 1,
                 memory: _20_GB,
+                gpus: 0,
                 session: session,
                 name: 'local',
                 pollInterval: 100
         )
 
         def task = new TaskRun()
         task.config = new TaskConfig(cpus: 1, memory: MemoryUnit.of('8GB'))
-        def handler = Mock(TaskHandler)
+        def handler = Mock(LocalTaskHandler)
         handler.getTask() >> { task }
         handler.canForkProcess() >> true
         handler.isReady() >> true
@@ -167,6 +171,7 @@ class LocalPollingMonitorTest extends Specification {
                 cpus: 10,
                 capacity: 20,
                 memory: _20_GB,
+                gpus: 0,
                 session: session,
                 name: 'local',
                 pollInterval: 100
@@ -195,6 +200,7 @@ class LocalPollingMonitorTest extends Specification {
                 cpus: 10,
                 capacity: 20,
                 memory: _20_GB,
+                gpus: 0,
                 session: session,
                 name: 'local',
                 pollInterval: 100