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Re-use Java VM if it already exists
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JNI prohibits creating multiple Java VM within a single process.
JNI_CreateJavaVM returns JNI_EEXIST error if Java VM already exists.
In that case, we have to re-use the existing Java VM by calling JNI_GetCreatedJavaVM.
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@choplin
choplin committed May 30, 2023
1 parent ec26734 commit 5ff5323
Showing 1 changed file with 169 additions and 35 deletions.
204 changes: 169 additions & 35 deletions jq.c
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,8 @@
/* POSTGRES_TO_UNIX_EPOCH_DAYS to microseconds */
#define POSTGRES_TO_UNIX_EPOCH_USECS (POSTGRES_TO_UNIX_EPOCH_DAYS * USECS_PER_DAY)

#define JNI_VERSION JNI_VERSION_1_2

/*
* Local housekeeping functions and Java objects
*/
Expand Down Expand Up @@ -105,6 +107,20 @@ static void jdbc_attach_jvm();
*/
static void jdbc_detach_jvm();

/*
* Get JNIEnv from JavaVM
*/
static void jdbc_get_jni_env(void);

/*
* Add classpath to system class loader using reflection
*/
static void jdbc_add_classpath_to_system_class_loader(char *classpath);

/*
* Get the maximum heap size for JVM by calling Runtime.getRuntime().maxMemory()
*/
static long jdbc_get_max_heap_size();
/*
* SIGINT interrupt check and process function
*/
Expand Down Expand Up @@ -277,6 +293,135 @@ jdbc_detach_jvm()
(*jvm)->DetachCurrentThread(jvm);
}

static void jdbc_get_jni_env(void)
{
int JVMEnvStat;

ereport(DEBUG3, (errmsg("In jdbc_get_jni_env")));

JVMEnvStat = (*jvm)->GetEnv(jvm, (void **) &Jenv, JNI_VERSION);
if (JVMEnvStat == JNI_EDETACHED)
{
ereport(DEBUG3, (errmsg("JVMEnvStat: JNI_EDETACHED; the current thread is not attached to the VM")));
jdbc_attach_jvm();
}
else if (JVMEnvStat == JNI_OK)
{
ereport(DEBUG3, (errmsg("JVMEnvStat: JNI_OK")));
}
else if (JVMEnvStat == JNI_EVERSION)
{
ereport(ERROR, (errmsg("JVMEnvStat: JNI_EVERSION; the specified version is not supported")));
}
}

static void jdbc_add_classpath_to_system_class_loader(char *classpath)
{
int url_classpath_len;
char *url_classpath;
jclass ClassLoader_class;
jmethodID ClassLoader_getSystemClassLoader;
jobject system_class_loader;
jclass URLClassLoader_class;
jmethodID URLClassLoader_addURL;
jclass URL_class;
jmethodID URL_constructor;
jobject url;

ereport(DEBUG3, errmsg("In jdbc_add_classpath_to_system_class_loader"));

url_classpath_len = 5 + strlen(classpath) + 2; /* "file:" + classpath + '/\0' */
url_classpath = (char *)palloc0(url_classpath_len);
snprintf(url_classpath, url_classpath_len, "file:%s/", classpath);


ClassLoader_class = (*Jenv)->FindClass(Jenv, "java/lang/ClassLoader");
if (ClassLoader_class == NULL) {
ereport(ERROR, errmsg("java/lang/ClassLoader is not found"));
}

ClassLoader_getSystemClassLoader = (*Jenv)->GetStaticMethodID(Jenv, ClassLoader_class,
"getSystemClassLoader", "()Ljava/lang/ClassLoader;");
if (ClassLoader_getSystemClassLoader == NULL) {
ereport(ERROR, errmsg("ClassLoader.getSystemClassLoader is not found"));
}

URLClassLoader_class = (*Jenv)->FindClass(Jenv, "java/net/URLClassLoader");
if (URLClassLoader_class == NULL) {
ereport(ERROR, errmsg("java/net/URLClassLoader is not found"));
}

URLClassLoader_addURL = (*Jenv)->GetMethodID(Jenv, URLClassLoader_class,
"addURL", "(Ljava/net/URL;)V");
if (URLClassLoader_addURL == NULL) {
ereport(ERROR, errmsg("URLClassLoader.addURL is not found"));
}

URL_class = (*Jenv)->FindClass(Jenv, "java/net/URL");
if (URL_class == NULL) {
ereport(ERROR, errmsg("java/net/URL is not found"));
}

URL_constructor = (*Jenv)->GetMethodID(Jenv, URL_class,
"<init>", "(Ljava/lang/String;)V");
if (URL_constructor == NULL) {
ereport(ERROR, errmsg("URL.<init> is not found"));
}

jq_exception_clear();
system_class_loader = (*Jenv)->CallStaticObjectMethod(
Jenv, ClassLoader_class, ClassLoader_getSystemClassLoader);
jq_get_exception();

jq_exception_clear();
url = (*Jenv)->NewObject(Jenv, URL_class, URL_constructor, (*Jenv)->NewStringUTF(Jenv, url_classpath));
jq_get_exception();

jq_exception_clear();
(*Jenv)->CallVoidMethod(Jenv, system_class_loader, URLClassLoader_addURL, url);
jq_get_exception();

ereport(DEBUG3, errmsg("Add classpath to System Class Loader: %s", url_classpath));
}

static long jdbc_get_max_heap_size()
{
jclass Runtime_class;
jmethodID Runtime_getRuntime;
jobject runtime;
jmethodID Runtime_maxMemory;
jlong max_memory;

ereport(DEBUG3, errmsg("entering function %s", __func__));

Runtime_class = (*Jenv)->FindClass(Jenv, "java/lang/Runtime");
if (Runtime_class == NULL) {
ereport(ERROR, errmsg("java/lang/Runtime is not found"));
}

Runtime_getRuntime = (*Jenv)->GetStaticMethodID(Jenv, Runtime_class,
"getRuntime", "()Ljava/lang/Runtime;");
if (Runtime_getRuntime == NULL) {
ereport(ERROR, errmsg("Runtime.getRuntime is not found"));
}

Runtime_maxMemory = (*Jenv)->GetMethodID(Jenv, Runtime_class, "maxMemory", "()J");
if (Runtime_maxMemory == NULL) {
ereport(ERROR, errmsg("Runtime.maxMemory is not found"));
}

jq_exception_clear();
runtime = (*Jenv)->CallStaticObjectMethod(Jenv, Runtime_class,
Runtime_getRuntime);
jq_get_exception();

jq_exception_clear();
max_memory = (*Jenv)->CallLongMethod(Jenv, runtime, Runtime_maxMemory);
jq_get_exception();

return max_memory;
}

/*
* jdbc_jvm_init Create the JVM which will be used for calling the Java
* routines that use JDBC to connect and access the foreign database.
Expand All @@ -293,9 +438,8 @@ jdbc_jvm_init(const ForeignServer * server, const UserMapping * user)
* whether JVM has been correctly created or
* not */
JavaVMInitArgs vm_args;
JavaVMOption *options;
JavaVMOption *options = NULL;
char strpkglibdir[] = STR_PKGLIBDIR;
char *classpath;
char *maxheapsizeoption = NULL;

opts.maxheapsize = 0;
Expand All @@ -308,62 +452,52 @@ jdbc_jvm_init(const ForeignServer * server, const UserMapping * user)

if (FunctionCallCheck == false)
{
classpath = (char *) palloc0(strlen(strpkglibdir) + 19);
snprintf(classpath, strlen(strpkglibdir) + 19, "-Djava.class.path=%s", strpkglibdir);

if (opts.maxheapsize != 0)
{ /* If the user has given a value for setting
* the max heap size of the JVM */
options = (JavaVMOption *) palloc0(sizeof(JavaVMOption) * 2);
options = (JavaVMOption *) palloc0(sizeof(JavaVMOption));
maxheapsizeoption = (char *) palloc0(sizeof(int) + 6);
snprintf(maxheapsizeoption, sizeof(int) + 6, "-Xmx%dm", opts.maxheapsize);
options[0].optionString = classpath;
options[1].optionString = maxheapsizeoption;
vm_args.nOptions = 2;
options[0].optionString = maxheapsizeoption;
vm_args.nOptions = 1;
}
else
{
options = (JavaVMOption *) palloc0(sizeof(JavaVMOption));
options[0].optionString = classpath;
vm_args.nOptions = 1;
vm_args.nOptions = 0;
}
vm_args.version = JNI_VERSION_1_2;
vm_args.version = JNI_VERSION;
vm_args.options = options;
vm_args.ignoreUnrecognized = JNI_FALSE;

/* Create the Java VM */
res = JNI_CreateJavaVM(&jvm, (void **) &Jenv, &vm_args);
if (res < 0)
if (res == JNI_EEXIST) {
res = JNI_GetCreatedJavaVMs(&jvm, 1, NULL);
if (res < 0) {
ereport(ERROR, errmsg("Failed to get created Java VM"));
}
jdbc_get_jni_env();
jdbc_add_classpath_to_system_class_loader(strpkglibdir);
ereport(INFO, errmsg("Java VM has already been created by another extension. "
"The existing Java VM will be re-used. "
"The max heapsize may be different from the setting value. "
"The current max heapsize is %ld bytes", jdbc_get_max_heap_size()));
}
else if (res < 0)
{
ereport(ERROR,
(errmsg("Failed to create Java VM")
));
ereport(ERROR, (errmsg("Failed to create Java VM")));
} else {
ereport(DEBUG3, (errmsg("Successfully created a JVM with %d MB heapsize", opts.maxheapsize)));
jdbc_add_classpath_to_system_class_loader(strpkglibdir);
}
ereport(DEBUG3, (errmsg("Successfully created a JVM with %d MB heapsize", opts.maxheapsize)));
InterruptFlag = false;
/* Register an on_proc_exit handler that shuts down the JVM. */
on_proc_exit(jdbc_destroy_jvm, 0);
FunctionCallCheck = true;
}
else
{
int JVMEnvStat;

vm_args.version = JNI_VERSION_1_2;
JVMEnvStat = (*jvm)->GetEnv(jvm, (void **) &Jenv, vm_args.version);
if (JVMEnvStat == JNI_EDETACHED)
{
ereport(DEBUG3, (errmsg("JVMEnvStat: JNI_EDETACHED; the current thread is not attached to the VM")));
jdbc_attach_jvm();
}
else if (JVMEnvStat == JNI_OK)
{
ereport(DEBUG3, (errmsg("JVMEnvStat: JNI_OK")));
}
else if (JVMEnvStat == JNI_EVERSION)
{
ereport(ERROR, (errmsg("JVMEnvStat: JNI_EVERSION; the specified version is not supported")));
}
jdbc_get_jni_env();
}
}

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