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wasm: correct a memleak caused by a shadowed var in the previous checkin. Add a stack-like allocator, sqlite3.capi.wasm.pstack, as a faster way of managing short-lived pointers (like the one which got shadowed).

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FossilOrigin-Name: 1fa019c88deac6b6e5155b620bdab1d7145846290daafb9adbefcf4f0fe542cf
This commit is contained in:
stephan
2022-10-01 18:47:42 +00:00
parent 32781427d7
commit 3afad4d432
5 changed files with 232 additions and 35 deletions
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106
ext/wasm/api/sqlite3-api-prologue.js
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@ -738,30 +738,92 @@ self.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
["sqlite3_wasm_vfs_unlink", "int", "string"]
];
/**
sqlite3.capi.wasm.pstack (pseudo-stack) holds a special-case
stack-style allocator intended only for use with _small_ data of
not more than (in total) a few kb in size, managed as if it were
stack-based.
It has only a single intended usage:
```
const stackPos = pstack.pointer;
try{
const ptr = pstack.alloc(8);
// ==> pstack.pointer === ptr
const otherPtr = pstack.alloc(8);
// ==> pstack.pointer === otherPtr
...
}finally{
pstack.restore(stackPos);
// ==> pstack.pointer === stackPos
}
```
This allocator is much faster than a general-purpose one but is
limited to usage patterns like the one shown above.
It operates from a static range of memory which lives outside of
space managed by Emscripten's stack-management, so does not
collide with Emscripten-provided stack allocation APIs. The
memory lives in the WASM heap and can be used with routines such
as wasm.setMemValue() and any wasm.heap8u().slice().
*/
capi.wasm.pstack = Object.assign(Object.create(null),{
/**
Sets the current ppstack position to the given pointer.
Results are undefined if the passed-in value did not come from
this.pointer.
*/
restore: capi.wasm.exports.sqlite3_wasm_pstack_restore,
/**
Attempts to allocate the given number of bytes from the
pstack. On success, it zeroes out a block of memory of the
given size, adjusts the pstack pointer, and returns a pointer
to the memory. On error, returns 0. The memory must eventually
be released using restore().
This method always adjusts the given value to be a multiple
of 8 in order to keep alignment guarantees.
*/
alloc: capi.wasm.exports.sqlite3_wasm_pstack_alloc
});
/**
sqlite3.capi.wasm.pstack.pointer resolves to the current pstack
position pointer. This value is intended _only_ to be passed to restore().
*/
Object.defineProperty(capi.wasm.pstack, 'pointer', {
configurable: false, iterable: true, writeable: false,
get: capi.wasm.exports.sqlite3_wasm_pstack_ptr
//Whether or not a setter as an alternative to restore() is
//clearer or would just lead to confusion is unclear.
//set: capi.wasm.exports.sqlite3_wasm_pstack_restore
});
/**
sqlite3.capi.wasm.pstack.remaining resolves to the amount of
space remaining in the pstack.
*/
Object.defineProperty(capi.wasm.pstack, 'remaining', {
configurable: false, iterable: true, writeable: false,
get: capi.wasm.exports.sqlite3_wasm_pstack_remaining
});
/** State for sqlite3_wasmfs_opfs_dir(). */
let __persistentDir = undefined;
/**
An experiment. Do not use in client code.
If the wasm environment has a persistent storage directory,
its path is returned by this function. If it does not then
it returns "" (noting that "" is a falsy value).
If the wasm environment has a WASMFS/OPFS-backed persistent
storage directory, its path is returned by this function. If it
does not then it returns "" (noting that "" is a falsy value).
The first time this is called, this function inspects the current
environment to determine whether persistence filesystem support
is available and, if it is, enables it (if needed).
environment to determine whether persistence support is available
and, if it is, enables it (if needed).
This function currently only recognizes the WASMFS/OPFS storage
combination. "Plain" OPFS is provided via a separate VFS which
is optionally be installed via sqlite3.asyncPostInit().
TODOs and caveats:
- If persistent storage is available at the root of the virtual
filesystem, this interface cannot currently distinguish that
from the lack of persistence. That can (in the mean time)
happen when using the JS-native "opfs" VFS, as opposed to the
WASMFS/OPFS combination.
combination and its path refers to storage rooted in the
Emscripten-managed virtual filesystem.
*/
capi.sqlite3_wasmfs_opfs_dir = function(){
if(undefined !== __persistentDir) return __persistentDir;
@ -879,10 +941,10 @@ self.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
if(!pDb) toss('Invalid sqlite3* argument.');
const wasm = capi.wasm;
if(!wasm.bigIntEnabled) toss('BigInt64 support is not enabled.');
const scope = wasm.scopedAllocPush();
const stack = wasm.pstack.pointer();
let pOut;
try{
const pSize = wasm.scopedAlloc(8/*i64*/ + wasm.ptrSizeof);
const pSize = wasm.pstack.alloc(8/*i64*/ + wasm.ptrSizeof);
const ppOut = pSize + 8;
/**
Maintenance reminder, since this cost a full hour of grief
@ -891,8 +953,6 @@ self.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
export reads a garbage size because it's not on an 8-byte
memory boundary!
*/
wasm.setPtrValue(ppOut, 0);
wasm.setMemValue(pSize, 0, 'i64');
let rc = wasm.exports.sqlite3_wasm_db_serialize(
pDb, ppOut, pSize, 0
);
@ -900,7 +960,7 @@ self.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
toss("Database serialization failed with code",
sqlite3.capi.sqlite3_web_rc_str(rc));
}
const pOut = wasm.getPtrValue(ppOut);
pOut = wasm.getPtrValue(ppOut);
const nOut = wasm.getMemValue(pSize, 'i64');
rc = nOut
? wasm.heap8u().slice(pOut, pOut + Number(nOut))
@ -911,7 +971,7 @@ self.sqlite3ApiBootstrap = function sqlite3ApiBootstrap(
throw w;
}finally{
if(pOut) wasm.exports.sqlite3_free(pOut);
wasm.scopedAllocPop(scope);
wasm.pstack.restore(stack);
}
};