Add more tests to NonBlockingSemaphore and make boolean semaphore release atomic

Author: smola

dd-java-agent/agent-iast/src/main/java/com/datadog/iast/overhead/OverheadController.java

@@ -4,7 +4,6 @@
 
 import com.datadog.iast.IastRequestContext;
 import com.datadog.iast.IastSystem;
-import datadog.trace.util.NonBlockingSemaphore;
 import datadog.trace.api.Config;
 import datadog.trace.api.gateway.RequestContext;
 import datadog.trace.api.gateway.RequestContextSlot;
@@ -13,6 +12,7 @@
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
 import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.util.AgentTaskScheduler;
+import datadog.trace.util.NonBlockingSemaphore;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
 import javax.annotation.Nullable;

internal-api/src/main/java/datadog/trace/util/NonBlockingSemaphore.java

@@ -66,7 +66,7 @@ public boolean acquire(final int count) {
     @Override
     public int release(final int count) {
       reset();
-      return available();
+      return 1;
     }
 
     @Override

internal-api/src/test/groovy/datadog/trace/util/NonBlockingSemaphoreTest.groovy

@@ -1,15 +1,15 @@
 package datadog.trace.util
 
-import datadog.trace.test.util.DDSpecification
 import groovy.transform.CompileDynamic
+import spock.lang.Specification
 
 import java.util.concurrent.Callable
 import java.util.concurrent.CountDownLatch
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
 
 @CompileDynamic
-class NonBlockingSemaphoreTest extends DDSpecification {
+class NonBlockingSemaphoreTest extends Specification {
 
   void 'test that the semaphore controls access to a shared resource (#permitCount)'(final int permitCount) {
     given:
@@ -71,6 +71,40 @@ class NonBlockingSemaphoreTest extends DDSpecification {
     2           | _
   }
 
+  void 'can never acquire more permits than the total'(final int permitCount) {
+    given:
+    final semaphore = NonBlockingSemaphore.withPermitCount(permitCount)
+
+    when:
+    final acquired = semaphore.acquire(permitCount+1)
+
+    then:
+    !acquired
+
+    where:
+    permitCount | _
+    1           | _
+    2           | _
+  }
+
+  void 'can perform extra releases'(final int permitCount) {
+    given:
+    final semaphore = NonBlockingSemaphore.withPermitCount(permitCount)
+
+    when:
+    for (int i = 0; i < permitCount * 2; i++) {
+      assert semaphore.release() == permitCount
+    }
+
+    then:
+    semaphore.available() == permitCount
+
+    where:
+    permitCount | _
+    1           | _
+    2           | _
+  }
+
   void 'reset helps recover when there is starvation (#permitCount)'(final int permitCount) {
     given:
     final semaphore = NonBlockingSemaphore.withPermitCount(permitCount)
@@ -107,6 +141,31 @@ class NonBlockingSemaphoreTest extends DDSpecification {
     acquired == threads
     semaphore.available() == Integer.MAX_VALUE
 
+    when:
+    int availableAfterRelease = semaphore.release()
+
+    then:
+    availableAfterRelease == Integer.MAX_VALUE
+    semaphore.available() == Integer.MAX_VALUE
+
+    when:
+    semaphore.reset()
+
+    then:
+    semaphore.available() == Integer.MAX_VALUE
+  }
+
+  void 'cannot create a semaphore without at least 1 permit'() {
+    when:
+    NonBlockingSemaphore.withPermitCount(0)
 
+    then:
+    thrown(AssertionError)
+
+    when:
+    NonBlockingSemaphore.withPermitCount(-1)
+
+    then:
+    thrown(AssertionError)
   }
 }