fix: EXPOSED-133 Suspend transactions blocking Hikari connection pool (…

…JetBrains#1837)

* fix: EXPOSED-133 Suspend transactions blocking Hikari connection pool

If the maximumPoolSize of a HikariDataSource is reached, the active connections
made through newSuspendedTransaction() are not being released back into the pool,
leading to a connection timeout exception when attempting to get more connections.

resetIfClosed(), in suspendedTransactionAsyncInternal(), calls getConnection() to
check if the transaction is closed (may happen after a repetition attempt), so
that it can be properly reset for a new attempt.

This blocks the connections being released and should not be necessary for the
first loop, as the created transaction has an open connection.

resetIfClosed() is now only accessed on subsequent repetition attempt loops.

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/transactions/experimental/Suspended.kt

@@ -162,6 +162,7 @@ private fun Transaction.resetIfClosed(): Transaction {
     }
 }
 
+@Suppress("CyclomaticComplexMethod")
 private fun <T> TransactionScope.suspendedTransactionAsyncInternal(
     shouldCommit: Boolean,
     statement: suspend Transaction.() -> T
@@ -172,7 +173,7 @@ private fun <T> TransactionScope.suspendedTransactionAsyncInternal(
 
     var answer: T
     while (true) {
-        val transaction = tx.value.resetIfClosed()
+        val transaction = if (repetitions == 0) tx.value else tx.value.resetIfClosed()
 
         @Suppress("TooGenericExceptionCaught")
         try {

exposed-tests/build.gradle.kts

@@ -24,6 +24,7 @@ dependencies {
     implementation("org.apache.logging.log4j", "log4j-core", Versions.log4j2)
     implementation("junit", "junit", "4.12")
     implementation("org.hamcrest", "hamcrest-library", "1.3")
+    implementation("com.zaxxer", "HikariCP", "5.0.1")
     implementation("org.jetbrains.kotlinx", "kotlinx-coroutines-debug", Versions.kotlinCoroutines)
 
     implementation("org.testcontainers", "mysql", Versions.testContainers)

exposed-tests/src/test/kotlin/org/jetbrains/exposed/sql/tests/h2/ConnectionPoolTests.kt

@@ -0,0 +1,70 @@
+package org.jetbrains.exposed.sql.tests.h2
+
+import com.zaxxer.hikari.HikariConfig
+import com.zaxxer.hikari.HikariDataSource
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import org.jetbrains.exposed.dao.IntEntity
+import org.jetbrains.exposed.dao.IntEntityClass
+import org.jetbrains.exposed.dao.id.EntityID
+import org.jetbrains.exposed.dao.id.IntIdTable
+import org.jetbrains.exposed.sql.Database
+import org.jetbrains.exposed.sql.SchemaUtils
+import org.jetbrains.exposed.sql.tests.TestDB
+import org.jetbrains.exposed.sql.tests.shared.assertEquals
+import org.jetbrains.exposed.sql.transactions.experimental.newSuspendedTransaction
+import org.jetbrains.exposed.sql.transactions.transaction
+import org.junit.Assume
+import org.junit.Test
+
+class ConnectionPoolTests {
+    private val hikariDataSource1 by lazy {
+        HikariDataSource(
+            HikariConfig().apply {
+                jdbcUrl = "jdbc:h2:mem:hikariDB1"
+                maximumPoolSize = 10
+            }
+        )
+    }
+
+    private val hikariDB1 by lazy {
+        Database.connect(hikariDataSource1)
+    }
+
+    @Test
+    fun testSuspendTransactionsExceedingPoolSize() {
+        Assume.assumeTrue(TestDB.H2 in TestDB.enabledInTests())
+        transaction(db = hikariDB1) {
+            SchemaUtils.create(TestTable)
+        }
+
+        val exceedsPoolSize = (hikariDataSource1.maximumPoolSize * 2 + 1).coerceAtMost(50)
+        runBlocking {
+            repeat(exceedsPoolSize) {
+                launch {
+                    newSuspendedTransaction {
+                        delay(100)
+                        TestEntity.new { testValue = "test$it" }
+                    }
+                }
+            }
+        }
+
+        transaction(db = hikariDB1) {
+            assertEquals(exceedsPoolSize, TestEntity.all().toList().count())
+
+            SchemaUtils.drop(TestTable)
+        }
+    }
+
+    object TestTable : IntIdTable("HIKARI_TESTER") {
+        val testValue = varchar("test_value", 32)
+    }
+
+    class TestEntity(id: EntityID<Int>) : IntEntity(id) {
+        companion object : IntEntityClass<TestEntity>(TestTable)
+
+        var testValue by TestTable.testValue
+    }
+}