Stephen Bovy created HDFS-10412:
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Summary: Add optional non-thread support for better perfromance
Key: HDFS-10412
URL: https://issues.apache.org/jira/browse/HDFS-10412
Project: Hadoop HDFS
Issue Type: Improvement
Components: libhdfs
Reporter: Stephen Bovy
Priority: Minor
I would like to propose some simple optional changes that would be activated by
a compiler flag. These changes would enable a typical monolithic single
threaded application to use libhdfs without the need to incur additional
overhead for threads that is not needed.
Here is a proposed for these changes:
#1 add a new function to "jni_helper.c"
/** getSoloJNIEnv: A helper function to get the JNIEnv* for non-threaded use.
* If no JVM exists, then one will be created. JVM command line arguments
* are obtained from the LIBHDFS_OPTS environment variable.
* @param: None.
* @return The JNIEnv* for non-thread use.
* */
JNIEnv* getSoloJNIEnv(void)
{
JNIEnv *env;
env = getGlobalJNIEnv();
if (!env) {
fprintf(stderr, "getJNIEnv: getGlobalJNIEnv failed\n");
return NULL;
}
return env;
}
Add the following the following to "hdfs.c"
#1 a static global variable : "JNIEnv* hdfsJNIEnv;"
#2 a MACRO: "GETJNIENV();"
#ifdef NOTHREAD
static JNIEnv* hdfsJNIEnv = NULL;
#define GETJNIENV() \
if (hdfsJNIEnv == NULL) { \
hdfsJNIEnv = getSoloJNIEnv(); \
} \
env = hdfsJNIEnv;
#else
#define GETJNIENV() env = getJNIEnv();
#endif
The above NEW MACRO would be used as in the following example:
int hdfsFileGetReadStatistics(hdfsFile file,
struct hdfsReadStatistics **stats)
{
jthrowable jthr;
jobject readStats = NULL;
jvalue jVal;
struct hdfsReadStatistics *s = NULL;
int ret;
JNIEnv* env;
// JNIEnv* env = getJNIEnv();
GETJNIENV();
( ... )
}
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