GlueGen is a compiler
for function and data-structure declarations, generating Java and JNI C
code offline at compile time and allows using native libraries within
your Java application.
It reads ANSI C header files and separate configuration files which
provide control over many aspects of the glue code generation. GlueGen
uses a complete ANSI C parser and an internal representation (IR)
capable of representing all C types to represent the APIs for which it
generates interfaces. It has the ability to perform significant
transformations on the IR before glue code emission.
GlueGen can produce native foreign function bindings to Java as well
as map native data structures to be fully accessible from Java including
potential calls to embedded function pointer.
GlueGen is also capable to bind even low-level APIs such as the Java
Native Interface (JNI) and the AWT Native Interface (JAWT) back up to
the Java programming language.
GlueGen utilizes JCPP, migrated C
preprocessor written in Java.
Gluegen has build-in types (terminal symbols) for:
type
java-bits
native-bits x32
native bits x64
type
signed
origin
void
0
0
0
void
void
ANSI-C
char
8
8
8
integer
any
ANSI-C
short
16
16
16
integer
any
ANSI-C
int
32
32
32
integer
any
ANSI-C
long
64
32
32†
integer
any
ANSI-C - Windows
long
64
32
64
integer
any
ANSI-C - Unix
float
32
32
32
float
signed
ANSI-C
double
64
64
64
double
signed
ANSI-C
__int32
32
32
32
integer
any
windows
__int64
64
64
64
integer
any
windows
int8_t
8
8
8
integer
signed
stdint.h
uint8_t
8
8
8
integer
unsigned
stdint.h
int16_t
16
16
16
integer
signed
stdint.h
uint16_t
16
16
16
integer
unsigned
stdint.h
int32_t
32
32
32
integer
signed
stdint.h
uint32_t
32
32
32
integer
unsigned
stdint.h
int64_t
64
64
64
integer
signed
stdint.h
uint64_t
64
64
64
integer
unsigned
stdint.h
intptr_t
64
32
64
integer
signed
stdint.h
uintptr_t
64
32
64
integer
unsigned
stdint.h
ptrdiff_t
64
32
64
integer
signed
stddef.h
size_t
64
32
64
integer
unsigned
stddef.h
wchar_t
32
32
32
integer
signed
stddef.h
Warning: Try to avoid unspecified bit sized types,
especially long, since it differs on Unix and
Windows! Notes:
† Type long will result in broken code on Windows,
since we don't differentiate the OS and it's bit size is ambiguous.
Anonymous void-pointer void* are mapped to NIO
Buffer.
Pointers to pointer-size types like intptr_t*,
uintptr_t*, ptrdiff_t* and size_t* are mapped
to PointerBuffer, to reflect the architecture depending storage
size.
String Mapping
Function return String
values
Function return values are currently mapped from char*
to Java String using UTF-8 via JNI function
FIXME: This might need more flexibility in case UTF-8 is not
suitable for 8-bit wide char mappings or wide characters,
e.g. for UTF-16 needs to be supported.
Function argument String
values
Function argument values are either mapped from char* to
Java String using UTF-8 via JNI function
String value mapping for Struct fields is performed
solely from the Java side using Charset and is hence most
flexible.
By default, UTF-8 is being used for getter and setter of
String values.
The Struct class provides two methods to get and set the used
Charset for conversion
/** Returns the Charset for this class's String mapping, default is StandardCharsets.UTF_8. */
public static Charset getCharset() { return _charset; };
/** Sets the Charset for this class's String mapping, default is StandardCharsets.UTF_8. */
public static void setCharset(Charset cs) { _charset = cs; }
In case the String length has not been configured via
ReturnedArrayLength, it will be dynamically calculated via
strnlen(aptr, max_len).
The maximum length default for the strnlen(..) operation is
8192 bytes and can be get and set using:
/** Returns the maximum number of bytes to read to determine native string length using `strnlen(..)`, default is 8192. */
public static int getMaxStrnlen() { return _max_strnlen; };
/** Sets the maximum number of bytes to read to determine native string length using `strnlen(..)`, default is 8192. */
public static void setMaxStrnlen(int v) { _max_strnlen = v; }
FIXME: This only works reliable using an 8-bit Charset
encoding, e.g. the default UTF-8.
Alignment for Compound Data
In general, depending on CPU and it's configuration (OS), alignment
is set up for each type (char, short, int, long, ..).
Compounds (structures) are aligned naturally, i.e. their inner
components are aligned
and are itself aligned to it's largest element.
Function Pointer, a typedef'ed and set callable
function pointer
A field may be a direct aggregation, i.e. instance, within the struct
including an array or a reference to a single element or array via a
pointer.
Both, primitive and struct field type mappings only
produce pure Java code, utilizing the GlueGen Runtime. Hence no
additional native code must be compiled nor a resulting additional
library loaded to use the mapping.
Only when mapping function-pointer within structs,
additional native glue-code is produced to call the underlying native
function which has to be compiled and its library loaded.
The generated method
public static boolean usesNativeCode() can be used to
validate whether the produced Java class requires a corresponding
library for additional native code.
GlueGen Struct Settings
ImmutableAccesssymbol
Immutable access can be set for a whole struct or a single field of a
struct.
Immutable access will simply suppress generating setters in the Java
code and hence also reduces the footprint of the generated Java class
for such struct.
ImmutableAccess TK_Struct
Immutable access for the whole struct `TK_Struct
Sets pseudo-code flag ImmutableAccess, see below.
ImmutableAccess TK_Struct.val
Immutable access for the single field val within struct
TK_Struct
Sets pseudo-code flag ImmutableAccess, see below.
MaxOneElementsymbol
MaxOneElement TK_Struct.val
Sets field pointer val to point to a array with a
maximum of one element and unset initial value (zero elements).
Sets pseudo-code flag MaxOneElement, see below.
ReturnedArrayLengthsymbolexpression
ReturnedArrayLength TK_Struct.val 3
Sets field pointer val to point to a array with three
elements.
Sets pseudo-code flag ConstElemCount, see below.
Having set ConstElemCount also implies native
ownership for a Pointer referenced native
memory.
ReturnedArrayLength TK_Struct.val 1
Sets field pointer val to point to a array with one
element.
Sets pseudo-code flags ConstElemCount and
MaxOneElement, see below.
Having set ConstElemCount also implies native
ownership for a Pointer referenced native
memory.
Sets field pointer val to point to a array with a
variable length as described by the field valElements
retrievable via its getter getValElements().
Sets pseudo-code flag VariaElemCount, see below.
ReturnsStringsymbol
A direct C code char array or indirect array via pointer
can be interpreted as a Java String.
ReturnsString TK_Struct.name
Sets field char-array or char-pointer name to be
additionally interpreted as a Java String. Besides the
byte[] and ByteBuffer getter and setter
variants, a String variant will be added.
Sets field char-array or char-pointer name to be
exclusively interpreted as a Java String. Instead of the
byte[] and ByteBuffer getter and setter
variants, a String variant will be produced.
ConstElemCount via ReturnedArrayLength
<int> implies native ownership for a
Pointer referenced native memory if the expression is
constant. Otherwise the native memory has java
ownership. See ReturnedArrayLength
Setting above.
To release native memory with java ownership, i.e. a
native ByteBuffer, releaseVal() can be used.
To shrink a Pointer & VariaElemCount
pointer-array elemCount size with java ownership , the memory
must be cleared with releaseVal() first. This is due to
setVal(src, srcPos, destPos, len) reusing the existing
memory in case destPos + len < elemCount.
Struct Java Signature Table
Please find below signature table as generated by the C
Declaration including its C Modifier, e.g.
const for constant, [const] for const and
non-const and empty for non-const (variable).
Further, the GlueGen Setting (see above) impacts the code
generation as well.
Below table demonstrates primitive types being mapped within
a struct named TK_Struct. A similar mapping is
produced for struct types, i.e. compounds.
C Mod
C Declaration
Java Setter
Java Getter
GlueGen Setting
Ownership
Remarks
static boolean usesNativeCode()
Java, static, true if using
native code
static int size()
Java, static, native size in
bytes
static TK_Struct create()
Java, static ctor
static TK_Struct create(ByteBuffer)
Java, static ctor w/ existing
ByteBuffer
static TK_Struct derefPointer(long
addr)
Java, static ctor dereferencing
ByteBuffer at native address of size()
ByteBuffer getBuffer()
Java, underlying ByteBuffer
long getDirectBufferAddress()
Java, native address of underlying
getBuffer()
int32_t val
setVal(int v)
int getVal()
Static
const
int32_t val
none
int getVal()
Static
Read only
int32_t val
none
int getVal()
ImmutableAccess
Static
Read only
[const]
int32_t* val
setVal(int v) releaseVal()
int getVal() boolean isValNull()
int getValElemCount()
MaxOneElement
Java
Starts w/ null elements, max 1
element
const
int32_t* val
none
int getVal() boolean isValNull()
static int getValElemCount()
ReturnedArrayLength
1
Native
Const element count 1
int32_t* val
setVal(int v)
int getVal() boolean isValNull()
static int getValElemCount()
ReturnedArrayLength
1
Native
Const element count 1
int32_t val[3]
setVal(int[] src, int srcPos, int destPos,
int len)
IntBuffer getVal() int[] getVal(int
srcPos, int[] dest, int destPos, int len)
Static
const
int32_t val[3]
none
IntBuffer getVal() int[] getVal(int
srcPos, int[] dest, int destPos, int len)
Static
Read only
const
int32_t* val
none
IntBuffer getVal() int[] getVal(int
srcPos, int[] dest, int destPos, int len) boolean isValNull()
static int getValElemCount()
ReturnedArrayLength
3
Native
Read only Const element count 3
int32_t* val
setVal(int[] src, int srcPos, int destPos,
int len)
IntBuffer getVal() int[] getVal(int
srcPos, int[] dest, int destPos, int len) boolean isValNull()
static int getValElemCount()
ReturnedArrayLength
3
Native
Const element count 3
[const]
int32_t* val
setVal(int[] src, int srcPos, int destPos,
int len) releaseVal()
IntBuffer getVal() int[] getVal(int
srcPos, int[] dest, int destPos, int len) boolean isValNull()
int getValElemCount()
Java
Starts w/ null elements
[const]
int32_t* val
setVal(int[] src, int srcPos, int destPos,
int len) releaseVal()
IntBuffer getVal() int[] getVal(int
srcPos, int[] dest, int destPos, int len) boolean isValNull()
ReturnedArrayLength
getValCount()
Ambiguous
Variable element count using field
valCount, which has getter and setter
[const]
char* name
setName(String srcVal)
releaseVal()
String getName() boolean isNameNull()
int getNameElemCount()
ReturnsStringOnly
Java
String only, w/ EOS
[const]
char* name
setName(String srcVal) setName(byte[]
src, int srcPos, int destPos, int len) releaseVal()
String getNameAsString() ByteBuffer
getName() boolean isNameNull() int getNameElemCount()
