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More Java docs about making use of the aggregate context. Change the JNI mapping to set the sqlite3_context::aggregateContext member directly, instead of via a superflous setter, because that way is faster.

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FossilOrigin-Name: 7af0cb998f7161296d5e5e50a42e9db26ec13c145c61194a999a1a0104818d45
This commit is contained in:
stephan 2023-07-28 09:25:05 +00:00
parent 75d3b1b5a2
commit 09c2640fe3
6 changed files with 84 additions and 60 deletions
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44
ext/jni/src/c/sqlite3-jni.c
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@ -275,7 +275,7 @@ struct NphCacheLine {
jmethodID midSet /* setNativePointer() */;
jmethodID midGet /* getNativePointer() */;
jmethodID midCtor /* constructor */;
jmethodID midSetAgg /* sqlite3_context::setAggregateContext() */;
jfieldID fidSetAgg /* sqlite3_context::aggregateContext */;
};
typedef struct JNIEnvCacheLine JNIEnvCacheLine;
@ -745,11 +745,14 @@ static void * getNativePointer(JNIEnv * env, jobject pObj, const char *zClassNam
Requires that jCx be a Java-side sqlite3_context wrapper for pCx.
This function calls sqlite3_aggregate_context() to allocate a tiny
sliver of memory, the address of which is set in
jCx->setAggregateContext(). The memory is only used as a key for
mapping, client-side, results of aggregate result sets across
xStep() and xFinal() methods.
jCx->aggregateContext. The memory is only used as a key for
mapping client-side results of aggregate result sets across
calls to the UDF's callbacks.
isFinal must be 1 for xFinal() calls and 0 for all others.
isFinal must be 1 for xFinal() calls and 0 for all others, the
difference being that the xFinal() invocation will not allocate
new memory if it was not already, resulting in a value of 0
for jCx->aggregateContext.
Returns 0 on success. Returns SQLITE_NOMEM on allocation error,
noting that it will not allocate when isFinal is true. It returns
@ -759,35 +762,34 @@ static void * getNativePointer(JNIEnv * env, jobject pObj, const char *zClassNam
static int udf_setAggregateContext(JNIEnv * env, jobject jCx,
sqlite3_context * pCx,
int isFinal){
jmethodID setter;
jfieldID member;
void * pAgg;
int rc = 0;
struct NphCacheLine * const cacheLine =
S3Global_nph_cache(env, ClassNames.sqlite3_context);
if(cacheLine && cacheLine->klazz && cacheLine->midSetAgg){
setter = cacheLine->midSetAgg;
assert(setter);
if(cacheLine && cacheLine->klazz && cacheLine->fidSetAgg){
member = cacheLine->fidSetAgg;
assert(member);
}else{
jclass const klazz =
cacheLine ? cacheLine->klazz : (*env)->GetObjectClass(env, jCx);
setter = (*env)->GetMethodID(env, klazz, "setAggregateContext", "(J)V");
member = (*env)->GetFieldID(env, klazz, "aggregateContext", "J");
if( !member ){
IFTHREW{ EXCEPTION_REPORT; EXCEPTION_CLEAR; }
return s3jni_db_error(sqlite3_context_db_handle(pCx),
SQLITE_ERROR,
"Internal error: cannot find "
"sqlite3_context::aggregateContext field.");
}
if(cacheLine){
assert(cacheLine->klazz);
assert(!cacheLine->midSetAgg);
cacheLine->midSetAgg = setter;
assert(!cacheLine->fidSetAgg);
cacheLine->fidSetAgg = member;
}
}
pAgg = sqlite3_aggregate_context(pCx, isFinal ? 0 : 4);
if( pAgg || isFinal ){
(*env)->CallVoidMethod(env, jCx, setter, (jlong)pAgg);
IFTHREW {
EXCEPTION_REPORT;
EXCEPTION_CLEAR/*arguable, but so is propagation*/;
rc = s3jni_db_error(sqlite3_context_db_handle(pCx),
SQLITE_ERROR,
"sqlite3_context::setAggregateContext() "
"unexpectedly threw.");
}
(*env)->SetLongField(env, jCx, member, (jlong)pAgg);
}else{
assert(!pAgg);
rc = SQLITE_NOMEM;

12
ext/jni/src/org/sqlite/jni/SQLFunction.java
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@ -35,11 +35,17 @@ public abstract class SQLFunction {
such mappings.
This class works by mapping
sqlite3_context::getAggregateContext() to a single piece of state
which persists across a "matching set" of the UDF's callbacks.
sqlite3_context.getAggregateContext() to a single piece of
state, of a client-defined type (the T part of this class), which
persists across a "matching set" of the UDF's callbacks.
This class is a helper providing commonly-needed functionality -
it is not required for use with aggregate or window functions.
Client UDFs are free to perform such mappings using custom
approaches.
*/
public static final class ContextMap<T> {
private java.util.Map<Long,ValueHolder<T>> map
private final java.util.Map<Long,ValueHolder<T>> map
= new java.util.HashMap<>();
/**

1
ext/jni/src/org/sqlite/jni/Tester1.java
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@ -656,7 +656,6 @@ public class Tester1 {
}
private static void testBusy(){
outln("testBusy()...");
final String dbName = "_busy-handler.db";
final sqlite3 db1 = new sqlite3();
final sqlite3 db2 = new sqlite3();

67
ext/jni/src/org/sqlite/jni/sqlite3_context.java
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@ -15,39 +15,56 @@ package org.sqlite.jni;
/**
sqlite3_context instances are used in conjunction with user-defined
SQL functions (a.k.a. UDFs). They are opaque pointers.
The getAggregateContext() method corresponds to C's
sqlite3_aggregate_context(), with a slightly different interface in
order to account for cross-language differences. It serves the same
purposes in a slightly different way: it provides a key which is
stable across invocations of UDF xStep() and xFinal() pairs, to
which a UDF may map state across such calls (e.g. a numeric result
which is being accumulated).
SQL functions (a.k.a. UDFs).
*/
public class sqlite3_context extends NativePointerHolder<sqlite3_context> {
public sqlite3_context() {
super();
}
private long aggcx = 0;
/**
If this object is being used in the context of an aggregate or
window UDF, the UDF binding layer will set a unique context value
here, else this will return 0. That value will be the same across
matching calls to the UDF callbacks. This value can be used as a
key to map state which needs to persist across such calls, noting
that such state should be cleaned up via xFinal().
*/
public long getAggregateContext(){
return aggcx;
}
/**
For use only by the JNI layer. It's permitted to call this even
For use only by the JNI layer. It's permitted to set this even
though it's private.
*/
private void setAggregateContext(long n){
aggcx = n;
private long aggregateContext = 0;
/**
getAggregateContext() corresponds to C's
sqlite3_aggregate_context(), with a slightly different interface
to account for cross-language differences. It serves the same
purposes in a slightly different way: it provides a key which is
stable across invocations of "matching sets" of a UDF's callbacks,
such that all calls into those callbacks can determine which "set"
of those calls they belong to.
If this object is being used in the context of an aggregate or
window UDF, this function returns a non-0 value which is distinct
for each set of UDF callbacks from a single invocation of the
UDF, otherwise it returns 0. The returned value is only only
valid within the context of execution of a single SQL statement,
and may be re-used by future invocations of the UDF in different
SQL statements.
Consider this SQL, where MYFUNC is a user-defined aggregate function:
SELECT MYFUNC(A), MYFUNC(B) FROM T;
The xStep() and xFinal() methods of the callback need to be able
to differentiate between those two invocations in order to
perform their work properly. The value returned by
getAggregateContext() will be distinct for each of those
invocations of MYFUNC() and is intended to be used as a lookup
key for mapping callback invocations to whatever client-defined
state is needed by the UDF.
There is one case where this will return 0 in the context of an
aggregate or window function: if the result set has no rows,
the UDF's xFinal() will be called without any other x...() members
having been called. In that one case, no aggregate context key will
have been generated. xFinal() implementations need to be prepared to
accept that condition as legal.
*/
public long getAggregateContext(){
return aggregateContext;
}
}

18
manifest
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@ -1,5 +1,5 @@
C More\sdocs\sand\scleanups\srelated\sto\sthe\saggregate\sUDF\sstate.\sCorrect\sthe\sOOM\scheck\sto\sbehave\sproperly\sif\sxFinal()\sis\scalled\swithout\sa\smatching\sxStep(),\sxValue(),\sor\sxInverse().
D 2023-07-28T01:51:14.668
C More\sJava\sdocs\sabout\smaking\suse\sof\sthe\saggregate\scontext.\sChange\sthe\sJNI\smapping\sto\sset\sthe\ssqlite3_context::aggregateContext\smember\sdirectly,\sinstead\sof\svia\sa\ssuperflous\ssetter,\sbecause\sthat\sway\sis\sfaster.
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# Remove this line to create a well-formed Fossil manifest.

2
manifest.uuid
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