Allow prefetching of a range of mapped file

include/inc_linux/jni_md.h

@@ -20,5 +20,6 @@ typedef long long jlong;
 #endif
 
 typedef signed char jbyte;
+typedef unsigned char jboolean;
 
 #endif /* !_JAVASOFT_JNI_MD_H_ */

include/inc_mac/jni_md.h

@@ -19,5 +19,6 @@ typedef long jint;
 #endif
 typedef long long jlong;
 typedef signed char jbyte;
+typedef unsigned char jboolean;
 
 #endif /* !_JAVASOFT_JNI_MD_H_ */

include/inc_win/jni_md.h

@@ -15,5 +15,6 @@
 typedef long jint;
 typedef __int64 jlong;
 typedef signed char jbyte;
+typedef unsigned char jboolean;
 
 #endif /* !_JAVASOFT_JNI_MD_H_ */

larray-mmap/src/main/java/xerial/larray/impl/LArrayNative.c

@@ -109,7 +109,7 @@ JNIEXPORT void JNICALL Java_xerial_larray_impl_LArrayNative_munmap
 
 
 JNIEXPORT void JNICALL Java_xerial_larray_impl_LArrayNative_msync
-(JNIEnv *env, jclass cls, jlong fd, jlong addr, jlong size) {
+  (JNIEnv *env, jclass cls, jlong fd, jlong addr, jlong size) {
 
 #if defined(_WIN32) || defined(_WIN64)
   void *a = (void *) addr;
@@ -161,3 +161,17 @@ JNIEXPORT jlong JNICALL Java_xerial_larray_impl_LArrayNative_duplicateHandle
 #endif
 
   }
+
+JNIEXPORT jboolean JNICALL Java_xerial_larray_impl_LArrayNative_prefetch
+  (JNIEnv *env, jclass cls, jlong addr, jlong size) {
+
+#if defined(_WIN32) || defined(_WIN64)
+  WIN32_MEMORY_RANGE_ENTRY range = {(PVOID) addr, (SIZE_T) size};
+  // PrefetchVirtualMemory returns non-zero on success
+  return PrefetchVirtualMemory(GetCurrentProcess(), 1, &range, 0) != 0 ? JNI_TRUE : JNI_FALSE;
+#else
+  // posix_madvise returns zero on success
+  return posix_madvise((void *) addr, (size_t) size, POSIX_MADV_WILLNEED) == 0 ? JNI_TRUE : JNI_FALSE;
+#endif
+
+}

larray-mmap/src/main/java/xerial/larray/impl/LArrayNative.java

@@ -37,4 +37,5 @@ public class LArrayNative {
     public static native void munmap(long address, long size);
     public static native void msync(long handle, long address, long size);
     public static native long duplicateHandle(long handle);
+    public static native boolean prefetch(long address, long size);
 }

larray-mmap/src/main/java/xerial/larray/mmap/MMapBuffer.java

@@ -121,6 +121,24 @@ public void close() throws IOException {
         fc.close();
     }
 
+    /**
+     * Attempts to prefetch the specified range in memory so that followup
+     * accesses do not incur I/O. This method is best-effort: there are no
+     * guarantees that the JVM and the OS will honor this request, and even
+     * if they do there are no guarantees for how long the data in the range
+     * will remain in memory before being paged out. When this method
+     * returns the prefetch operation may be still ongoing.
+     * You should only attempt to prefetch data you are going to access soon,
+     * and most likely length should be significantly smaller than the size of
+     * the page cache.
+     * This method returns false if the prefetch request could not be issued
+     * to the OS; true otherwise. Note that the best-effort behavior described
+     * above applies even if prefetch returns true.
+     */
+    public bool prefetch(long offset, long length) {
+        return LArrayNative.prefetch(m.headerAddress()+offset, length);
+    }
+
     protected long offset() {
         return pagePosition;
     }