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8366093: [lworld] Add preview mode to C++ classloader #1618

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8366093: [lworld] Add preview mode to C++ classloader #1618

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180 changes: 116 additions & 64 deletions src/hotspot/share/classfile/classLoader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -96,9 +96,18 @@ static JImageClose_t JImageClose = nullptr;
static JImageFindResource_t JImageFindResource = nullptr;
static JImageGetResource_t JImageGetResource = nullptr;

// JimageFile pointer, or null if exploded JDK build.
// JImageFile pointer, or null if exploded JDK build.
static JImageFile* JImage_file = nullptr;

// JImageMode status to control preview behaviour. JImage_file is unusable
// for normal lookup until (JImage_mode != JIMAGE_MODE_UNINITIALIZED).
enum JImageMode {
JIMAGE_MODE_UNINITIALIZED = 0,
JIMAGE_MODE_DEFAULT = 1,
JIMAGE_MODE_ENABLE_PREVIEW = 2
};
static JImageMode JImage_mode = JIMAGE_MODE_UNINITIALIZED;

// Globals

PerfCounter* ClassLoader::_perf_accumulated_time = nullptr;
Expand Down Expand Up @@ -153,7 +162,7 @@ void ClassLoader::print_counters(outputStream *st) {

GrowableArray<ModuleClassPathList*>* ClassLoader::_patch_mod_entries = nullptr;
GrowableArray<ModuleClassPathList*>* ClassLoader::_exploded_entries = nullptr;
ClassPathEntry* ClassLoader::_jrt_entry = nullptr;
ClassPathImageEntry* ClassLoader::_jrt_entry = nullptr;

ClassPathEntry* volatile ClassLoader::_first_append_entry_list = nullptr;
ClassPathEntry* volatile ClassLoader::_last_append_entry = nullptr;
Expand All @@ -170,15 +179,6 @@ static bool string_starts_with(const char* str, const char* str_to_find) {
}
#endif

static const char* get_jimage_version_string() {
static char version_string[10] = "";
if (version_string[0] == '\0') {
jio_snprintf(version_string, sizeof(version_string), "%d.%d",
VM_Version::vm_major_version(), VM_Version::vm_minor_version());
}
return (const char*)version_string;
}

bool ClassLoader::string_ends_with(const char* str, const char* str_to_find) {
size_t str_len = strlen(str);
size_t str_to_find_len = strlen(str_to_find);
Expand Down Expand Up @@ -233,6 +233,73 @@ Symbol* ClassLoader::package_from_class_name(const Symbol* name, bool* bad_class
return SymbolTable::new_symbol(name, pointer_delta_as_int(start, base), pointer_delta_as_int(end, base));
}

// --------------------------------
// The following jimage_xxx static functions encapsulate all JImage_file and JImage_mode access.
// This is done to make it easy to reason about the JImage file state (exists vs initialized etc.).

// Opens the named JImage file and sets the JImage file reference.
// Returns true if opening the JImage file was successful (see also jimage_exists()).
static bool jimage_open(const char* modules_path) {
// Currently 'error' is not set to anything useful, so ignore it here.
jint error;
JImage_file = (*JImageOpen)(modules_path, &error);
return JImage_file != nullptr;
}

// Closes and clears the JImage file reference (this will only be called during shutdown).
static void jimage_close() {
if (JImage_file != nullptr) {
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I'm not familiar with jimage at all, is there as reason we could close a non-open jimage? And following from that, can we guarantee to not call jimage_open on an open jimage? (Maybe an assert should guard it?)

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I honestly don't know, so this is the old behaviour, so I'm keeping it for now.
Alan might know more.

(*JImageClose)(JImage_file);
JImage_file = nullptr;
}
}

// Returns whether a JImage file was opened (but NOT whether it was initialized yet).
static bool jimage_exists() {
return JImage_file != nullptr;
}

// Returns the JImage file reference (which may or may not be initialized).
static JImageFile* jimage_non_null() {
assert(jimage_exists(), "should have been opened by ClassLoader::lookup_vm_options "
"and remained throughout normal JVM lifetime");
return JImage_file;
}

// Called once to set the access mode for resource (i.e. preview or non-preview) before
// general resource lookup can occur.
static void jimage_init(bool enable_preview) {
assert(JImage_mode == JIMAGE_MODE_UNINITIALIZED, "jimage_init must not be called twice");
JImage_mode = enable_preview ? JIMAGE_MODE_ENABLE_PREVIEW : JIMAGE_MODE_DEFAULT;
}

// Returns true if jimage_init() has been called. Once the JImage file is initialized,
// jimage_is_preview_enabled() can be called to correctly determine the access mode.
static bool jimage_is_initialized() {
return jimage_exists() && JImage_mode != JIMAGE_MODE_UNINITIALIZED;
}

// Returns the access mode for an initialized JImage file (reflects --enable-preview).
static bool jimage_is_preview_enabled() {
assert(jimage_is_initialized(), "jimage is not initialized");
return JImage_mode == JIMAGE_MODE_ENABLE_PREVIEW;
}

// Looks up the location of a named JImage resource. This "raw" lookup function allows
// the preview mode to be manually specified, so must not be accessible outside this
// class. ClassPathImageEntry manages all calls for resources after startup is complete.
static JImageLocationRef jimage_find_resource(const char* module_name,
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This function makes the rest of the code more legible. Thanks!

const char* file_name,
bool is_preview,
jlong *size) {
return ((*JImageFindResource)(jimage_non_null(),
module_name,
file_name,
is_preview,
size));
}
// --------------------------------

// Given a fully qualified package name, find its defining package in the class loader's
// package entry table.
PackageEntry* ClassLoader::get_package_entry(Symbol* pkg_name, ClassLoaderData* loader_data) {
Expand Down Expand Up @@ -371,28 +438,15 @@ ClassFileStream* ClassPathZipEntry::open_stream(JavaThread* current, const char*

DEBUG_ONLY(ClassPathImageEntry* ClassPathImageEntry::_singleton = nullptr;)

JImageFile* ClassPathImageEntry::jimage() const {
return JImage_file;
}

JImageFile* ClassPathImageEntry::jimage_non_null() const {
assert(ClassLoader::has_jrt_entry(), "must be");
assert(jimage() != nullptr, "should have been opened by ClassLoader::lookup_vm_options "
"and remained throughout normal JVM lifetime");
return jimage();
}

void ClassPathImageEntry::close_jimage() {
if (jimage() != nullptr) {
(*JImageClose)(jimage());
JImage_file = nullptr;
}
jimage_close();
}

ClassPathImageEntry::ClassPathImageEntry(JImageFile* jimage, const char* name) :
ClassPathImageEntry::ClassPathImageEntry(const char* name) :
ClassPathEntry() {
guarantee(jimage != nullptr, "jimage file is null");
guarantee(jimage_is_initialized(), "jimage is not initialized");
guarantee(name != nullptr, "jimage file name is null");

assert(_singleton == nullptr, "VM supports only one jimage");
DEBUG_ONLY(_singleton = this);
size_t len = strlen(name) + 1;
Expand All @@ -411,16 +465,18 @@ ClassFileStream* ClassPathImageEntry::open_stream(JavaThread* current, const cha
// 2. A package is in at most one module in the jimage file.
//
ClassFileStream* ClassPathImageEntry::open_stream_for_loader(JavaThread* current, const char* name, ClassLoaderData* loader_data) {
bool is_preview = jimage_is_preview_enabled();

jlong size;
JImageLocationRef location = (*JImageFindResource)(jimage_non_null(), "", get_jimage_version_string(), name, &size);
JImageLocationRef location = jimage_find_resource("", name, is_preview, &size);

if (location == 0) {
TempNewSymbol class_name = SymbolTable::new_symbol(name);
TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name);

if (pkg_name != nullptr) {
if (!Universe::is_module_initialized()) {
location = (*JImageFindResource)(jimage_non_null(), JAVA_BASE_NAME, get_jimage_version_string(), name, &size);
location = jimage_find_resource(JAVA_BASE_NAME, name, is_preview, &size);
} else {
PackageEntry* package_entry = ClassLoader::get_package_entry(pkg_name, loader_data);
if (package_entry != nullptr) {
Expand All @@ -431,7 +487,7 @@ ClassFileStream* ClassPathImageEntry::open_stream_for_loader(JavaThread* current
assert(module->is_named(), "Boot classLoader package is in unnamed module");
const char* module_name = module->name()->as_C_string();
if (module_name != nullptr) {
location = (*JImageFindResource)(jimage_non_null(), module_name, get_jimage_version_string(), name, &size);
location = jimage_find_resource(module_name, name, is_preview, &size);
}
}
}
Expand All @@ -444,7 +500,7 @@ ClassFileStream* ClassPathImageEntry::open_stream_for_loader(JavaThread* current
char* data = NEW_RESOURCE_ARRAY(char, size);
(*JImageGetResource)(jimage_non_null(), location, data, size);
// Resource allocated
assert(this == (ClassPathImageEntry*)ClassLoader::get_jrt_entry(), "must be");
assert(this == ClassLoader::get_jrt_entry(), "must be");
return new ClassFileStream((u1*)data,
checked_cast<int>(size),
_name,
Expand All @@ -454,16 +510,9 @@ ClassFileStream* ClassPathImageEntry::open_stream_for_loader(JavaThread* current
return nullptr;
}

JImageLocationRef ClassLoader::jimage_find_resource(JImageFile* jf,
const char* module_name,
const char* file_name,
jlong &size) {
return ((*JImageFindResource)(jf, module_name, get_jimage_version_string(), file_name, &size));
}

bool ClassPathImageEntry::is_modules_image() const {
assert(this == _singleton, "VM supports a single jimage");
assert(this == (ClassPathImageEntry*)ClassLoader::get_jrt_entry(), "must be used for jrt entry");
assert(this == ClassLoader::get_jrt_entry(), "must be used for jrt entry");
return true;
}

Expand Down Expand Up @@ -618,14 +667,15 @@ void ClassLoader::setup_bootstrap_search_path_impl(JavaThread* current, const ch
struct stat st;
if (os::stat(path, &st) == 0) {
// Directory found
if (JImage_file != nullptr) {
if (jimage_exists()) {
assert(Arguments::has_jimage(), "sanity check");
const char* canonical_path = get_canonical_path(path, current);
assert(canonical_path != nullptr, "canonical_path issue");

_jrt_entry = new ClassPathImageEntry(JImage_file, canonical_path);
// Hand over lifecycle control of the JImage file to the _jrt_entry singleton
// (see ClassPathImageEntry::close_jimage). The image must be initialized by now.
_jrt_entry = new ClassPathImageEntry(canonical_path);
assert(_jrt_entry != nullptr && _jrt_entry->is_modules_image(), "No java runtime image present");
assert(_jrt_entry->jimage() != nullptr, "No java runtime image");
} // else it's an exploded build.
} else {
// If path does not exist, exit
Expand Down Expand Up @@ -1439,49 +1489,51 @@ void ClassLoader::initialize(TRAPS) {
setup_bootstrap_search_path(THREAD);
}

static char* lookup_vm_resource(JImageFile *jimage, const char *jimage_version, const char *path) {
jlong size;
JImageLocationRef location = (*JImageFindResource)(jimage, "java.base", jimage_version, path, &size);
if (location == 0)
return nullptr;
char *val = NEW_C_HEAP_ARRAY(char, size+1, mtClass);
(*JImageGetResource)(jimage, location, val, size);
val[size] = '\0';
return val;
}

// Lookup VM options embedded in the modules jimage file
char* ClassLoader::lookup_vm_options() {
jint error;
char modules_path[JVM_MAXPATHLEN];
const char* fileSep = os::file_separator();

// Initialize jimage library entry points
load_jimage_library();

jio_snprintf(modules_path, JVM_MAXPATHLEN, "%s%slib%smodules", Arguments::get_java_home(), fileSep, fileSep);
JImage_file =(*JImageOpen)(modules_path, &error);
if (JImage_file == nullptr) {
return nullptr;
if (jimage_open(modules_path)) {
// Special case where we lookup the options string *before* calling jimage_init().
// Since VM arguments have not been parsed, and the ClassPathImageEntry singleton
// has not been created yet, we access the JImage file directly in non-preview mode.
jlong size;
JImageLocationRef location =
jimage_find_resource(JAVA_BASE_NAME, "jdk/internal/vm/options", /* is_preview */ false, &size);
if (location != 0) {
char *options = NEW_C_HEAP_ARRAY(char, size+1, mtClass);
(*JImageGetResource)(jimage_non_null(), location, options, size);
options[size] = '\0';
return options;
}
}
return nullptr;
}

const char *jimage_version = get_jimage_version_string();
char *options = lookup_vm_resource(JImage_file, jimage_version, "jdk/internal/vm/options");
return options;
// Finishes initializing the JImageFile (if present) by setting the access mode.
void ClassLoader::init_jimage(bool enable_preview) {
if (jimage_exists()) {
jimage_init(enable_preview);
}
}

bool ClassLoader::is_module_observable(const char* module_name) {
assert(JImageOpen != nullptr, "jimage library should have been opened");
if (JImage_file == nullptr) {
if (!jimage_exists()) {
struct stat st;
const char *path = get_exploded_module_path(module_name, true);
bool res = os::stat(path, &st) == 0;
FREE_C_HEAP_ARRAY(char, path);
return res;
}
// We don't expect preview mode (i.e. --enable-preview) to affect module visibility.
jlong size;
const char *jimage_version = get_jimage_version_string();
return (*JImageFindResource)(JImage_file, module_name, jimage_version, "module-info.class", &size) != 0;
return jimage_find_resource(module_name, "module-info.class", /* is_preview */ false, &size) != 0;
}

jlong ClassLoader::classloader_time_ms() {
Expand Down
25 changes: 16 additions & 9 deletions src/hotspot/share/classfile/classLoader.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -99,19 +99,21 @@ class ClassPathZipEntry: public ClassPathEntry {
};


// For java image files
// A singleton path entry which takes ownership of the initialized JImageFile
// reference. Not used for exploded builds.
class ClassPathImageEntry: public ClassPathEntry {
private:
const char* _name;
DEBUG_ONLY(static ClassPathImageEntry* _singleton;)
public:
bool is_modules_image() const;
const char* name() const { return _name == nullptr ? "" : _name; }
JImageFile* jimage() const;
JImageFile* jimage_non_null() const;
// Called to close the JImage during os::abort (normally not called).
void close_jimage();
ClassPathImageEntry(JImageFile* jimage, const char* name);
// Takes effective ownership of the static JImageFile pointer.
ClassPathImageEntry(const char* name);
virtual ~ClassPathImageEntry() { ShouldNotReachHere(); }

ClassFileStream* open_stream(JavaThread* current, const char* name);
ClassFileStream* open_stream_for_loader(JavaThread* current, const char* name, ClassLoaderData* loader_data);
};
Expand Down Expand Up @@ -200,10 +202,10 @@ class ClassLoader: AllStatic {
static GrowableArray<ModuleClassPathList*>* _patch_mod_entries;

// 2. the base piece
// Contains the ClassPathEntry of the modular java runtime image.
// Contains the ClassPathImageEntry of the modular java runtime image.
// If no java runtime image is present, this indicates a
// build with exploded modules is being used instead.
static ClassPathEntry* _jrt_entry;
static ClassPathImageEntry* _jrt_entry;
static GrowableArray<ModuleClassPathList*>* _exploded_entries;
enum { EXPLODED_ENTRY_SIZE = 80 }; // Initial number of exploded modules

Expand Down Expand Up @@ -350,15 +352,20 @@ class ClassLoader: AllStatic {
static void append_boot_classpath(ClassPathEntry* new_entry);
#endif

// Retrieves additional VM options prior to flags processing. Options held
// in the JImage file are retrieved without fully initializing it. (this is
// the only JImage lookup which can succeed before init_jimage() is called).
static char* lookup_vm_options();

// Called once, after all flags are processed, to finish initializing the
// JImage file. Until this is called, jimage_find_resource(), and any other
// JImage resource lookups or access will fail.
static void init_jimage(bool enable_preview);

// Determines if the named module is present in the
// modules jimage file or in the exploded modules directory.
static bool is_module_observable(const char* module_name);

static JImageLocationRef jimage_find_resource(JImageFile* jf, const char* module_name,
const char* file_name, jlong &size);

static void trace_class_path(const char* msg, const char* name = nullptr);

// VM monitoring and management support
Expand Down
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