Add new methods to get current pid to KiwiEnvironment

* Add currentPid() and tryGetCurrentPid() to KiwiEnvironment
* Add default implementations of these methods in DefaultEnvironment

Closes #640

src/main/java/org/kiwiproject/base/DefaultEnvironment.java

@@ -124,6 +124,21 @@ public long nanoTime() {
         return System.nanoTime();
     }
 
+    @Override
+    public long currentPid() {
+        return ProcessHandle.current().pid();
+    }
+
+    @Override
+    public Optional<Long> tryGetCurrentPid() {
+        try {
+            return Optional.of(currentPid());
+        } catch (Exception e) {
+            LOG.trace("Unable to get current process ID", e);
+            return Optional.empty();
+        }
+    }
+
     /**
      * {@inheritDoc}
      * <p>

src/main/java/org/kiwiproject/base/KiwiEnvironment.java

@@ -161,6 +161,27 @@ public interface KiwiEnvironment {
      */
     long nanoTime();
 
+    /**
+     * Returns the process ID of the currently executing JVM. This method does not perform any error checking. Use
+     * {@link #tryGetCurrentPid()} for a version that returns an empty optional if it is unable to obtain the pid
+     * for any reason.
+     *
+     * @return the pid of the current process
+     * @see ProcessHandle#current()
+     * @see ProcessHandle#pid()
+     */
+    long currentPid();
+
+    /**
+     * Tries to obtain the process ID of the currently executing JVM. If any problem occurs, it is caught and an
+     * empty optional is returned.
+     *
+     * @return an optional containing the pid of the current process, or empty if <em>any</em> problem occurred
+     * @see ProcessHandle#current()
+     * @see ProcessHandle#pid()
+     */
+    Optional<Long> tryGetCurrentPid();
+
     /**
      * Returns the process ID of the currently executing JVM. This method does not perform any error checking. Use
      * {@link #tryGetCurrentProcessId()} for a safer version, which returns the result as an integer (wrapped in an

src/test/java/org/kiwiproject/base/DefaultEnvironmentTest.java

@@ -1,6 +1,8 @@
 package org.kiwiproject.base;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.anyLong;
@@ -10,6 +12,7 @@
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.kiwiproject.collect.KiwiMaps;
 
@@ -195,6 +198,49 @@ private void assertNow(long envNow, long now, long delta) {
                 .isLessThan(delta);
     }
 
+    @Nested
+    class CurrentPid {
+
+        @Test
+        void shouldGetCurrentPid() {
+            assertThatCode(() -> env.currentPid()).doesNotThrowAnyException();
+        }
+
+        @Test
+        void shouldAllowUnsupportedExceptionsToEscape() {
+            var envSpy = spy(env);
+            var errorMessage = "this fake JVM doesn't support getting the current pid for some reason";
+            doThrow(new UnsupportedOperationException(errorMessage))
+                    .when(envSpy)
+                    .currentPid();
+
+            assertThatThrownBy(envSpy::currentPid)
+                    .isExactlyInstanceOf(UnsupportedOperationException.class)
+                    .hasMessage(errorMessage);
+        }
+    }
+
+    @Nested
+    class TryGetCurrentPid {
+
+        @Test
+        void shouldReturnOptionalContainingPid() {
+            var optionalPid = env.tryGetCurrentPid();
+            assertThat(optionalPid).isPresent();
+        }
+
+        @Test
+        void shouldReturnEmptyOptional_WhenCurrentPidCannotBeObtained() {
+            var envSpy = spy(env);
+            doThrow(new UnsupportedOperationException("this fake JVM doesn't support getting the current pid for some reason"))
+                    .when(envSpy)
+                    .currentPid();
+
+            var optionalPid = envSpy.tryGetCurrentPid();
+            assertThat(optionalPid).isEmpty();
+        }
+    }
+
     @Test
     void testCurrentProcessId() {
         String pid = env.currentProcessId();