remove log4j dependency.

core/build.gradle.kts

@@ -15,8 +15,6 @@ dependencies {
   implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.1")
   implementation("com.github.ajalt.clikt:clikt:4.2.2")
   testImplementation("org.jetbrains.kotlin:kotlin-test")
-  implementation("org.apache.logging.log4j:log4j-core:2.23.1")
-  implementation("org.apache.logging.log4j:log4j-slf4j-impl:2.23.1")
   testCompileOnly(project(":runtime"))
 }
 

core/src/main/kotlin/org/pastalab/fray/core/RunContext.kt

@@ -35,7 +35,6 @@ class RunContext(val config: Configuration) {
   var mainExiting = false
   var nanoTime = System.nanoTime()
   val terminatingThread = mutableSetOf<Int>()
-  val logger = config.loggerContext.getLogger(RunContext::class.java)
   val hashCodeMapper = ReferencedContextManager<Int>({ config.randomnessProvider.nextInt() })
   var forkJoinPool: ForkJoinPool? = null
   private val lockManager = LockManager()
@@ -82,12 +81,13 @@ class RunContext(val config: Configuration) {
       } else {
         e.printStackTrace(PrintWriter(sw))
       }
-      logger.error(sw.toString())
+      config.frayLogger.error(sw.toString())
       if (config.exploreMode || config.noExitWhenBugFound) {
         return
       }
       if (!config.isReplay) {
-        logger.error("Error found, the recording is saved to ${config.report}/recording_0/")
+        config.frayLogger.error(
+            "Error found, the recording is saved to ${config.report}/recording_0/")
         println("Error found, you may find the error report in ${config.report}")
         config.saveToReportFolder(0)
       }

core/src/main/kotlin/org/pastalab/fray/core/TestRunner.kt

@@ -2,7 +2,6 @@ package org.pastalab.fray.core
 
 import java.util.*
 import kotlin.time.TimeSource
-import org.apache.logging.log4j.Logger
 import org.pastalab.fray.core.command.Configuration
 import org.pastalab.fray.core.randomness.ControlledRandom
 import org.pastalab.fray.core.scheduler.RandomScheduler
@@ -13,8 +12,6 @@ class TestRunner(val config: Configuration) {
   val context = RunContext(config)
   var currentDivision = 1
 
-  val logger: Logger = config.loggerContext.getLogger(TestRunner::class.java)
-
   init {
     context.bootstrap()
   }
@@ -44,7 +41,7 @@ class TestRunner(val config: Configuration) {
       val timeSource = TimeSource.Monotonic
       val start = timeSource.markNow()
       var i = 0
-      logger.info("Fray started.")
+      config.frayLogger.info("Fray started.")
       var bugsFound = 0
       if (config.dummyRun) {
         // We want to do a dummy-run first to make sure all variables are initialized
@@ -95,10 +92,10 @@ class TestRunner(val config: Configuration) {
           if (config.isReplay) {
             break
           }
-          logger.info(
+          config.frayLogger.info(
               "Error found at iter: $i, Elapsed time: ${(timeSource.markNow() - start).inWholeMilliseconds}ms",
           )
-          logger.info("The recording is saved to ${config.report}/recording_$i/")
+          config.frayLogger.info("The recording is saved to ${config.report}/recording_$i/")
           if (!config.exploreMode) {
             config.saveToReportFolder(i)
             break
@@ -107,7 +104,7 @@ class TestRunner(val config: Configuration) {
         i++
       }
       context.shutDown()
-      logger.info(
+      config.frayLogger.info(
           "Run finished. Total iter: $i, Elapsed time: ${(timeSource.markNow() - start).inWholeMilliseconds}ms",
       )
     }

core/src/main/kotlin/org/pastalab/fray/core/command/Configuration.kt

@@ -20,9 +20,7 @@ import kotlinx.serialization.json.JsonNamingStrategy
 import kotlinx.serialization.modules.SerializersModule
 import kotlinx.serialization.modules.polymorphic
 import kotlinx.serialization.modules.subclass
-import org.apache.logging.log4j.core.LoggerContext
-import org.apache.logging.log4j.core.config.Configurator
-import org.apache.logging.log4j.core.config.builder.api.ConfigurationBuilderFactory
+import org.pastalab.fray.core.logger.FrayLogger
 import org.pastalab.fray.core.observers.ScheduleObserver
 import org.pastalab.fray.core.observers.ScheduleRecorder
 import org.pastalab.fray.core.observers.ScheduleRecording
@@ -242,29 +240,7 @@ data class Configuration(
     scheduleObservers.forEach { it.saveToReportFolder("$report/recording_$index") }
   }
 
-  val loggerContext by lazy {
-    val builder = ConfigurationBuilderFactory.newConfigurationBuilder()
-    builder.setConfigurationName("Fray")
-    builder.setLoggerContext(LoggerContext("Fray"))
-    val standard = builder.newLayout("PatternLayout")
-    standard.addAttribute("pattern", "%d [%t] %-5level: %msg%n%throwable")
-    val appender =
-        if (isReplay) {
-          builder.newAppender("log", "Console").addAttribute("target", "SYSTEM_OUT").add(standard)
-        } else {
-          builder
-              .newAppender("log", "File")
-              .addAttribute("fileName", "${report}/fray.log")
-              .addAttribute("append", false)
-        }
-    appender.add(standard)
-    builder.add(appender)
-    val logger = builder.newLogger("org.pastalab.fray", "INFO")
-    logger.add(builder.newAppenderRef("log"))
-    logger.addAttribute("additivity", false)
-    builder.add(logger)
-    Configurator.initialize(builder.build())
-  }
+  val frayLogger = FrayLogger("$report/fray.log")
 
   init {
     if (!isReplay) {

core/src/main/kotlin/org/pastalab/fray/core/logger/FrayLogger.kt

@@ -0,0 +1,25 @@
+package org.pastalab.fray.core.logger
+
+import java.io.File
+import java.time.LocalDateTime
+import java.time.format.DateTimeFormatter
+
+class FrayLogger(location: String) {
+  val logFile = File(location)
+
+  @Synchronized
+  fun log(level: String, message: String) {
+    val currentDateTime =
+        LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"))
+    val logMessage = "$currentDateTime [$level]: $message\n"
+    logFile.appendText(logMessage)
+  }
+
+  fun info(message: String) {
+    log("INFO", message)
+  }
+
+  fun error(message: String) {
+    log("ERROR", message)
+  }
+}