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Allow IDX_... gaps in ModelConstants
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By allowing occasional gaps in the otherwise-consecutive
IDX_... values, new constants can be added as needed, and
kept in coherent groupings, with a smaller blast radius in
version control (and fewer merge conflicts for other branches
or forks), by avoiding extensive renumbering of otherwise
untouched members.
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@jcflack
jcflack committed Sep 8, 2023
1 parent 5e8fa13 commit e511a12
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Showing 2 changed files with 169 additions and 115 deletions.
2 changes: 1 addition & 1 deletion pljava-so/src/main/c/ModelConstants.c
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Original file line number Diff line number Diff line change
Expand Up @@ -356,7 +356,7 @@ StaticAssertStmt((expr) == \
CONFIRMSIZEOF( pg_attribute, attnotnull );
CONFIRMSIZEOF( pg_attribute, attisdropped );

CONFIRMCONST( Anum_pg_extension_oid );
CONFIRMATTNUM( pg_extension, oid );
CONFIRMCONST( ExtensionOidIndexId );

#undef CONFIRMSIZEOF
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282 changes: 168 additions & 114 deletions pljava/src/main/java/org/postgresql/pljava/pg/ModelConstants.java
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Original file line number Diff line number Diff line change
Expand Up @@ -31,8 +31,8 @@ public abstract class ModelConstants
{
/*
* C code will contain a static array of int initialized to the values
* that are needed. This native method will return a ByteBuffer windowing
* that static array.
* that are needed. The native method in this class obtains a ByteBuffer
* windowing that static array.
*
* To detect fat-finger mistakes, the array will include alternating indices
* and values { IDX_SIZEOF_DATUM, SIZEOF_DATUM, ... }, so when windowed as
Expand All @@ -42,6 +42,13 @@ public abstract class ModelConstants
* designated array initializers would offer a simpler, all-static approach,
* but PostgreSQL strives for C89 compatibility before PostgreSQL 12.
*
* As a practical matter, the sequence of IDX_... values is allowed to have
* gaps, so that new constants can be added as needed, coherently grouped,
* without requiring extensive renumbering of otherwise unaffected lines.
* The array cells remain consecutive, and this class simply tracks a gap
* between the IDX_... value and the physical position. This, of course,
* would complicate any move to C99 designated initializers.
*
* Starting with PostgreSQL 11, LLVM bitcode for the server might be found
* in $pkglibdir/bitcode/postgres, and that could one day pose opportunities
* for a PL/Java using an LLVM library, or depending on GraalVM, to access
Expand All @@ -50,9 +57,70 @@ public abstract class ModelConstants
* GraalVM, and hope that the bootstrapping needed here does not become too
* burdensome.
*/
private static class Natives
private static class Natives implements AutoCloseable
{
static native ByteBuffer _statics();
private IntBuffer b = _statics()
.asReadOnlyBuffer().order(nativeOrder()).asIntBuffer();
private int gap = 0;

/**
* Returns the next constant from the windowed array.
*<p>
* The next constant is determined by the buffer's current position,
* not by <var>index</var>, which is only used for sanity checking:
* <ol>
* <li>adjusted by the current "gap", it should be half the buffer's
* current position, and
* <li>unadjusted, it should equal the {@code int} read at
* that position.
* </ol>
* The {@code int} read at the next consecutive position is returned.
* @param index the expected index of the next constant to be read
* @return the next constant
* @throws ConstantsError if any sanity check fails
*/
int get(int index)
{
try
{
if ( b.position() != (index - gap) << 1 || index != b.get() )
throw new ConstantsError();
return b.get();
}
catch ( Exception e )
{
throw (ConstantsError)new ConstantsError().initCause(e);
}
}

/**
* Conforms the internal sanity checking to a gap in assigned indices.
*<p>
* The supplied <var>index</var> must be greater than that implied by
* the buffer's current position (and previously recorded gap, if any),
* and the difference is remembered as the new gap.
* @param index the assigned index of the next constant to be read
* @throws ConstantsError if the newly-computed gap is not larger than
* the remembered value
*/
void gap(int index)
{
int pos = b.position();
assert 0 == (pos & 1); // expected as get() always advances by two
index -= pos >>> 1;
if ( index <= gap )
throw new ConstantsError();
gap = index;
}

@Override
public void close()
{
if ( 0 < b.remaining() )
throw new ConstantsError();
}

private static native ByteBuffer _statics();
}

/*
Expand Down Expand Up @@ -105,10 +173,14 @@ private static class Natives

/*
* These constants (which will be included in a generated header available
* to the C code) are the indices into the 'statics' array where the various
* wanted values should be placed. Edits should keep them consecutive
* distinct small array indices; the checked() function in the static
* initializer will be checking for gaps or repeats.
* to the C code) are (almost) indices into the 'statics' array where the
* various wanted values should be placed. Edits should keep them distinct
* consecutive small array indices within related groups; gaps are allowed
* (and encouraged) between groups, so additions can be made without mass
* renumbering. The get() method of Natives, used in the static initializer,
* will be checking for gaps or repeats; the gap() method must be called
* where each gap occurs, to advise what the next expected IDX_... value
* is to be.
*/
@Native private static final int IDX_PG_VERSION_NUM = 0;

Expand Down Expand Up @@ -200,7 +272,7 @@ private static class Natives

/*
* These public statics are the values of interest, set at class
* initialization time by reading them from the buffer returned by _statics.
* initialization time by reading them from the buffer managed by Natives.
*/

/**
Expand Down Expand Up @@ -302,112 +374,94 @@ private static class Natives

static
{
IntBuffer b =
Natives._statics()
.asReadOnlyBuffer().order(nativeOrder()).asIntBuffer();

PG_VERSION_NUM = checked(b, IDX_PG_VERSION_NUM);

SIZEOF_DATUM = checked(b, IDX_SIZEOF_DATUM);
SIZEOF_SIZE = checked(b, IDX_SIZEOF_SIZE);

ALIGNOF_SHORT = checked(b, IDX_ALIGNOF_SHORT);
ALIGNOF_INT = checked(b, IDX_ALIGNOF_INT);
ALIGNOF_DOUBLE = checked(b, IDX_ALIGNOF_DOUBLE);
MAXIMUM_ALIGNOF = checked(b, IDX_MAXIMUM_ALIGNOF);

int n = checked(b, IDX_NAMEDATALEN);
NAMEDATALEN = (short)n;
assert n == NAMEDATALEN;

SIZEOF_varatt_indirect = checked(b, IDX_SIZEOF_varatt_indirect);
SIZEOF_varatt_expanded = checked(b, IDX_SIZEOF_varatt_expanded);
SIZEOF_varatt_external = checked(b, IDX_SIZEOF_varatt_external);

OFFSET_TTS_NVALID = checked(b, IDX_OFFSET_TTS_NVALID);
SIZEOF_TTS_NVALID = checked(b, IDX_SIZEOF_TTS_NVALID);

TTS_FLAG_EMPTY = checked(b, IDX_TTS_FLAG_EMPTY);
TTS_FLAG_FIXED = checked(b, IDX_TTS_FLAG_FIXED);
OFFSET_TTS_FLAGS = checked(b, IDX_OFFSET_TTS_FLAGS);

OFFSET_TTS_EMPTY = checked(b, IDX_OFFSET_TTS_EMPTY);
OFFSET_TTS_FIXED = checked(b, IDX_OFFSET_TTS_FIXED);

OFFSET_TTS_TABLEOID = checked(b, IDX_OFFSET_TTS_TABLEOID);

SIZEOF_FORM_PG_ATTRIBUTE = checked(b, IDX_SIZEOF_FORM_PG_ATTRIBUTE);
ATTRIBUTE_FIXED_PART_SIZE = checked(b, IDX_ATTRIBUTE_FIXED_PART_SIZE);
CLASS_TUPLE_SIZE = checked(b, IDX_CLASS_TUPLE_SIZE);
HEAPTUPLESIZE = checked(b, IDX_HEAPTUPLESIZE);

OFFSET_TUPLEDESC_ATTRS = checked(b, IDX_OFFSET_TUPLEDESC_ATTRS);
OFFSET_TUPLEDESC_TDREFCOUNT= checked(b,IDX_OFFSET_TUPLEDESC_TDREFCOUNT);
SIZEOF_TUPLEDESC_TDREFCOUNT= checked(b,IDX_SIZEOF_TUPLEDESC_TDREFCOUNT);
OFFSET_TUPLEDESC_TDTYPEID = checked(b, IDX_OFFSET_TUPLEDESC_TDTYPEID);
OFFSET_TUPLEDESC_TDTYPMOD = checked(b, IDX_OFFSET_TUPLEDESC_TDTYPMOD);

OFFSET_pg_attribute_atttypid
= checked(b, IDX_OFFSET_pg_attribute_atttypid);
OFFSET_pg_attribute_attlen
= checked(b, IDX_OFFSET_pg_attribute_attlen);
OFFSET_pg_attribute_attcacheoff
= checked(b, IDX_OFFSET_pg_attribute_attcacheoff);
OFFSET_pg_attribute_atttypmod
= checked(b, IDX_OFFSET_pg_attribute_atttypmod);
OFFSET_pg_attribute_attbyval
= checked(b, IDX_OFFSET_pg_attribute_attbyval);
OFFSET_pg_attribute_attalign
= checked(b, IDX_OFFSET_pg_attribute_attalign);
OFFSET_pg_attribute_attnotnull
= checked(b, IDX_OFFSET_pg_attribute_attnotnull);
OFFSET_pg_attribute_attisdropped
= checked(b, IDX_OFFSET_pg_attribute_attisdropped);

Anum_pg_class_reltype = checked(b, IDX_Anum_pg_class_reltype);

SIZEOF_MCTX = checked(b, IDX_SIZEOF_MCTX);
OFFSET_MCTX_isReset = checked(b, IDX_OFFSET_MCTX_isReset);
OFFSET_MCTX_mem_allocated = checked(b, IDX_OFFSET_MCTX_mem_allocated);
OFFSET_MCTX_parent = checked(b, IDX_OFFSET_MCTX_parent);
OFFSET_MCTX_firstchild = checked(b, IDX_OFFSET_MCTX_firstchild);
OFFSET_MCTX_prevchild = checked(b, IDX_OFFSET_MCTX_prevchild);
OFFSET_MCTX_nextchild = checked(b, IDX_OFFSET_MCTX_nextchild);
OFFSET_MCTX_name = checked(b, IDX_OFFSET_MCTX_name);
OFFSET_MCTX_ident = checked(b, IDX_OFFSET_MCTX_ident);

ATTNUM = checked(b, IDX_ATTNUM);
AUTHMEMMEMROLE = checked(b, IDX_AUTHMEMMEMROLE);
AUTHMEMROLEMEM = checked(b, IDX_AUTHMEMROLEMEM);
AUTHOID = checked(b, IDX_AUTHOID);
COLLOID = checked(b, IDX_COLLOID);
DATABASEOID = checked(b, IDX_DATABASEOID);
LANGOID = checked(b, IDX_LANGOID);
NAMESPACEOID = checked(b, IDX_NAMESPACEOID);
OPEROID = checked(b, IDX_OPEROID);
PROCOID = checked(b, IDX_PROCOID);
RELOID = checked(b, IDX_RELOID);
TSCONFIGOID = checked(b, IDX_TSCONFIGOID);
TSDICTOID = checked(b, IDX_TSDICTOID);
TYPEOID = checked(b, IDX_TYPEOID);

N_ACL_RIGHTS = checked(b, IDX_N_ACL_RIGHTS);

if ( 0 != b.remaining() )
throw new ConstantsError();
}

private static int checked(IntBuffer b, int index)
{
try
{
if ( b.position() != index << 1 || index != b.get() )
throw new ConstantsError();
return b.get();
}
catch ( Exception e )
try ( Natives n = new Natives() )
{
throw (ConstantsError)new ConstantsError().initCause(e);
PG_VERSION_NUM = n.get(IDX_PG_VERSION_NUM);

SIZEOF_DATUM = n.get(IDX_SIZEOF_DATUM);
SIZEOF_SIZE = n.get(IDX_SIZEOF_SIZE);

ALIGNOF_SHORT = n.get(IDX_ALIGNOF_SHORT);
ALIGNOF_INT = n.get(IDX_ALIGNOF_INT);
ALIGNOF_DOUBLE = n.get(IDX_ALIGNOF_DOUBLE);
MAXIMUM_ALIGNOF = n.get(IDX_MAXIMUM_ALIGNOF);

int c = n.get(IDX_NAMEDATALEN);
NAMEDATALEN = (short)c;
assert c == NAMEDATALEN;

SIZEOF_varatt_indirect = n.get(IDX_SIZEOF_varatt_indirect);
SIZEOF_varatt_expanded = n.get(IDX_SIZEOF_varatt_expanded);
SIZEOF_varatt_external = n.get(IDX_SIZEOF_varatt_external);

OFFSET_TTS_NVALID = n.get(IDX_OFFSET_TTS_NVALID);
SIZEOF_TTS_NVALID = n.get(IDX_SIZEOF_TTS_NVALID);

TTS_FLAG_EMPTY = n.get(IDX_TTS_FLAG_EMPTY);
TTS_FLAG_FIXED = n.get(IDX_TTS_FLAG_FIXED);
OFFSET_TTS_FLAGS = n.get(IDX_OFFSET_TTS_FLAGS);

OFFSET_TTS_EMPTY = n.get(IDX_OFFSET_TTS_EMPTY);
OFFSET_TTS_FIXED = n.get(IDX_OFFSET_TTS_FIXED);

OFFSET_TTS_TABLEOID = n.get(IDX_OFFSET_TTS_TABLEOID);

SIZEOF_FORM_PG_ATTRIBUTE = n.get(IDX_SIZEOF_FORM_PG_ATTRIBUTE);
ATTRIBUTE_FIXED_PART_SIZE = n.get(IDX_ATTRIBUTE_FIXED_PART_SIZE);
CLASS_TUPLE_SIZE = n.get(IDX_CLASS_TUPLE_SIZE);
HEAPTUPLESIZE = n.get(IDX_HEAPTUPLESIZE);

OFFSET_TUPLEDESC_ATTRS = n.get(IDX_OFFSET_TUPLEDESC_ATTRS);
OFFSET_TUPLEDESC_TDREFCOUNT= n.get(IDX_OFFSET_TUPLEDESC_TDREFCOUNT);
SIZEOF_TUPLEDESC_TDREFCOUNT= n.get(IDX_SIZEOF_TUPLEDESC_TDREFCOUNT);
OFFSET_TUPLEDESC_TDTYPEID = n.get(IDX_OFFSET_TUPLEDESC_TDTYPEID);
OFFSET_TUPLEDESC_TDTYPMOD = n.get(IDX_OFFSET_TUPLEDESC_TDTYPMOD);

OFFSET_pg_attribute_atttypid
= n.get(IDX_OFFSET_pg_attribute_atttypid);
OFFSET_pg_attribute_attlen
= n.get(IDX_OFFSET_pg_attribute_attlen);
OFFSET_pg_attribute_attcacheoff
= n.get(IDX_OFFSET_pg_attribute_attcacheoff);
OFFSET_pg_attribute_atttypmod
= n.get(IDX_OFFSET_pg_attribute_atttypmod);
OFFSET_pg_attribute_attbyval
= n.get(IDX_OFFSET_pg_attribute_attbyval);
OFFSET_pg_attribute_attalign
= n.get(IDX_OFFSET_pg_attribute_attalign);
OFFSET_pg_attribute_attnotnull
= n.get(IDX_OFFSET_pg_attribute_attnotnull);
OFFSET_pg_attribute_attisdropped
= n.get(IDX_OFFSET_pg_attribute_attisdropped);

Anum_pg_class_reltype = n.get(IDX_Anum_pg_class_reltype);

SIZEOF_MCTX = n.get(IDX_SIZEOF_MCTX);
OFFSET_MCTX_isReset = n.get(IDX_OFFSET_MCTX_isReset);
OFFSET_MCTX_mem_allocated = n.get(IDX_OFFSET_MCTX_mem_allocated);
OFFSET_MCTX_parent = n.get(IDX_OFFSET_MCTX_parent);
OFFSET_MCTX_firstchild = n.get(IDX_OFFSET_MCTX_firstchild);
OFFSET_MCTX_prevchild = n.get(IDX_OFFSET_MCTX_prevchild);
OFFSET_MCTX_nextchild = n.get(IDX_OFFSET_MCTX_nextchild);
OFFSET_MCTX_name = n.get(IDX_OFFSET_MCTX_name);
OFFSET_MCTX_ident = n.get(IDX_OFFSET_MCTX_ident);

ATTNUM = n.get(IDX_ATTNUM);
AUTHMEMMEMROLE = n.get(IDX_AUTHMEMMEMROLE);
AUTHMEMROLEMEM = n.get(IDX_AUTHMEMROLEMEM);
AUTHOID = n.get(IDX_AUTHOID);
COLLOID = n.get(IDX_COLLOID);
DATABASEOID = n.get(IDX_DATABASEOID);
LANGOID = n.get(IDX_LANGOID);
NAMESPACEOID = n.get(IDX_NAMESPACEOID);
OPEROID = n.get(IDX_OPEROID);
PROCOID = n.get(IDX_PROCOID);
RELOID = n.get(IDX_RELOID);
TSCONFIGOID = n.get(IDX_TSCONFIGOID);
TSDICTOID = n.get(IDX_TSDICTOID);
TYPEOID = n.get(IDX_TYPEOID);

N_ACL_RIGHTS = n.get(IDX_N_ACL_RIGHTS);
}
}

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