dedupe-02.js (1434B)
1 // AutoStableStringChars needs to prevent the owner of its chars from being 2 // deduplicated, even if they are held by a different string. 3 4 gczeal(0); 5 6 function makeExtensibleStrFrom(str) { 7 var left = str.substr(0, str.length/2); 8 var right = str.substr(str.length/2, str.length); 9 var ropeStr = left + right; 10 return ensureLinearString(ropeStr); 11 } 12 13 // Make a string to deduplicate to. 14 var original = makeExtensibleStrFrom('{ "phbbbbbbbbbbbbbbttt!!!!??": [1] }\n\n'); 15 16 // Construct D2 -> D1 -> base 17 var D2 = makeExtensibleStrFrom('{ "phbbbbbbbbbbbbbbttt!!!!??": [1] }'); 18 var D1 = newRope(D2, '\n', {nursery: true}); 19 ensureLinearString(D1); 20 var base = newRope(D1, '\n', {nursery: true}); 21 ensureLinearString(base); 22 23 // Make an AutoStableStringChars(D2) and do a minor GC within it. (This will do 24 // a major GC, but it'll start out with a minor GC.) `base` would get 25 // deduplicated to `original`, if it weren't for AutoStableStringChars marking 26 // all of D2, D1, and base non-deduplicatable. 27 28 // The first time JSON.parse runs, it will create several (14 in my test) GC 29 // things before getting to the point where it does an allocation while holding 30 // the chars pointer. Get them out of the way now. 31 JSON.parse(D2); 32 33 // Cause a minor GC to happen during JSON.parse after AutoStableStringChars 34 // gives up its pointer. 35 schedulegc(1); 36 JSON.parse(D2); 37 38 // Access `D2` to verify that it is not using the deduplicated chars. 39 print(D2);