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Internal JNI doc tweaks.

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FossilOrigin-Name: f4aa2c82882cb6be1fd52977de19fd03c2e38abb857b520f951b32d610972ab6
This commit is contained in:
stephan
2023-07-31 09:28:15 +00:00
parent 9c1c6da930
commit 41a7ac637a
3 changed files with 30 additions and 18 deletions
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34
ext/jni/src/c/sqlite3-jni.c
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@ -367,8 +367,8 @@ struct BusyHandlerJni{
*/
typedef struct PerDbStateJni PerDbStateJni;
struct PerDbStateJni {
JNIEnv *env;
sqlite3 * pDb;
JNIEnv *env /* The associated JNIEnv handle */;
sqlite3 *pDb /* The associated db handle */;
jobject jDb /* a global ref of the object which was passed to
sqlite3_open(_v2)(). We need this in order to have an
object to pass to sqlite3_collation_needed()'s
@ -377,8 +377,8 @@ struct PerDbStateJni {
would be a different instance (and maybe even a
different class) than the one the user expects to
receive. */;
PerDbStateJni * pNext;
PerDbStateJni * pPrev;
PerDbStateJni * pNext /* Next entry in the available/free list */;
PerDbStateJni * pPrev /* Previous entry in the available/free list */;
JniHookState trace;
JniHookState progress;
JniHookState commitHook;
@ -941,10 +941,13 @@ static int CollationState_xCompare(void *pArg, int nLhs, const void *lhs,
int nRhs, const void *rhs){
CollationState * const cs = pArg;
JNIEnv * env = cs->env;
jint rc;
jint rc = 0;
jbyteArray jbaLhs = (*env)->NewByteArray(env, (jint)nLhs);
jbyteArray jbaRhs = (*env)->NewByteArray(env, (jint)nRhs);
jbyteArray jbaRhs = jbaLhs ? (*env)->NewByteArray(env, (jint)nRhs) : NULL;
//MARKER(("native xCompare nLhs=%d nRhs=%d\n", nLhs, nRhs));
if(!jbaRhs){
(*env)->FatalError(env, "Out of memory. Cannot allocate arrays for collation.");
}
(*env)->SetByteArrayRegion(env, jbaLhs, 0, (jint)nLhs, (const jbyte*)lhs);
(*env)->SetByteArrayRegion(env, jbaRhs, 0, (jint)nRhs, (const jbyte*)rhs);
rc = (*env)->CallIntMethod(env, cs->oCollation, cs->midCompare,
@ -965,12 +968,21 @@ static void CollationState_xDestroy(void *pArg){
/* State for sqlite3_result_java_object() and
sqlite3_value_java_object(). */
typedef struct {
/* POTENTIAL bug: the JNI docs say that the JNIEnv pointer
is guaranteed to resolve the same for the same contexts,
but the docs are unclear as to whether it's the (JNIEnv *env)
or (*env) which resolves consistently.
/* The JNI docs say:
This posts claims it's unsave to cache JNIEnv at all, even when
https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/design.html
> The VM is guaranteed to pass the same interface pointer to a
native method when it makes multiple calls to the native method
from the same Java thread.
Per the accompanying diagram, the "interface pointer" is the
pointer-to-pointer which is passed to all JNI calls
(`JNIEnv *env`), implying that we need to be caching that. The
verbiage "interface pointer" implies, however, that we should be
storing the dereferenced `(*env)` pointer.
This posts claims it's unsafe to cache JNIEnv at all, even when
it's always used in the same thread:
https://stackoverflow.com/questions/12420463