Windows port for a semaphore data type.

semaphore_impl.cpp

#include "semaphore_impl.h"
#include <windows.h>

static const char* CLASS = "net/coderodde/util/concurrent/WindowsSemaphoreImpl";
static const char* FIELD = "semaphoreHandle";

static HANDLE get_semaphore_handle(JNIEnv* env, jobject obj)
{
	jclass clazz = env->FindClass(CLASS);
	jfieldID fid = env->GetFieldID(clazz, FIELD, "J");
	return (HANDLE) env->GetLongField(obj, fid); 
}

JNIEXPORT void JNICALL
Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_init(
	JNIEnv* env,
	jobject obj,
	jint maxCount,
	jint count)
{
	// Create a handle to a semaphore.
	HANDLE semaphore;
	semaphore = CreateSemaphore(NULL,
								count,
								maxCount,
								NULL);

	// Get to the 'semaphoreHandle' field.
	const jclass clazz = env->FindClass(CLASS);
	const jfieldID semaphore_field_id = env->GetFieldID(clazz, FIELD, "J");

	// Store the value of the semaphore to the Java semaphore object.
	env->SetLongField(obj, semaphore_field_id, (jlong) semaphore);
}

JNIEXPORT void JNICALL
Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_clean(
	JNIEnv* env,
	jobject obj)
{
	CloseHandle(get_semaphore_handle(env, obj));
}

JNIEXPORT void JNICALL
Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_lock(
	JNIEnv* env,
	jobject obj)
{
	WaitForSingleObject(get_semaphore_handle(env, obj), INFINITE);
}

JNIEXPORT void JNICALL
Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_unlock(
	JNIEnv* env,
	jobject obj)
{
	ReleaseSemaphore(get_semaphore_handle(env, obj), 1L, NULL);
}

semaphore_impl.h

#include <jni.h>

#ifndef WINDOWS_SEMAPHORE_IMPL_H
#define WINDOWS_SEMAPHORE_IMPL_H

#ifdef __cplusplus
extern "C" {
#endif

	JNIEXPORT void JNICALL
		Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_init(
			JNIEnv*,
			jobject,
			jint,
			jint);

	JNIEXPORT void JNICALL
		Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_clean(JNIEnv*, jobject);

	JNIEXPORT void JNICALL
		Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_lock(JNIEnv*, jobject);

	JNIEXPORT void JNICALL
		Java_net_coderodde_util_concurrent_WindowsSemaphoreImpl_unlock(JNIEnv*, jobject);

#ifdef __cplusplus
}
#endif

#endif // WINDOWS_SEMAPHORE_IMPL_H