toddlipcon commented on a change in pull request #597: HDFS-3246: pRead
equivalent for direct read path
URL: https://github.com/apache/hadoop/pull/597#discussion_r273629967
##########
File path:
hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfs/hdfs.c
##########
@@ -1571,6 +1651,51 @@ tSize hdfsPread(hdfsFS fs, hdfsFile f, tOffset position,
return jVal.i;
}
+tSize preadDirect(hdfsFS fs, hdfsFile f, tOffset position, void* buffer,
+ tSize length)
+{
+ // JAVA EQUIVALENT:
+ // ByteBuffer buf = ByteBuffer.allocateDirect(length) // wraps C buffer
+ // fis.read(position, buf);
+
+ jvalue jVal;
+ jthrowable jthr;
+ jobject bb;
+
+ //Get the JNIEnv* corresponding to current thread
+ JNIEnv* env = getJNIEnv();
+ if (env == NULL) {
+ errno = EINTERNAL;
+ return -1;
+ }
+
+ //Error checking... make sure that this file is 'readable'
+ if (f->type != HDFS_STREAM_INPUT) {
+ fprintf(stderr, "Cannot read from a non-InputStream object!\n");
+ errno = EINVAL;
+ return -1;
+ }
+
+ //Read the requisite bytes
+ bb = (*env)->NewDirectByteBuffer(env, buffer, length);
+ if (bb == NULL) {
+ errno = printPendingExceptionAndFree(env, PRINT_EXC_ALL,
+ "readDirect: NewDirectByteBuffer");
+ return -1;
+ }
+
+ jthr = invokeMethod(env, &jVal, INSTANCE, f->file,
+ JC_FS_DATA_INPUT_STREAM, "read", "(JLjava/nio/ByteBuffer;)I",
+ position, bb);
+ destroyLocalReference(env, bb);
+ if (jthr) {
+ errno = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+ "preadDirect: FSDataInputStream#read");
+ return -1;
+ }
+ return (jVal.i < 0) ? 0 : jVal.i;
Review comment:
it seems the javadoc says that the method can return 0 for a transient
zero-length result, and -1 for EOF. But here we're converting -1 to 0, so the
caller can't distinguish between a must-retry '0 length read' and a 'shouldn't
retry' EOF, right?
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