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/* this source code form is subject to the terms of the mozilla public
* license, v. 2.0. if a copy of the mpl was not distributed with this
/*
* This file helps tracking Javascript object allocations.
* It is only included in local builds as a debugging helper.
*
* It is typicaly used when running DevTools tests (either mochitests or DAMP).
* To use it, you need to set the following environment variable:
* DEBUG_DEVTOOLS_ALLOCATIONS="normal"
* This will only print the number of JS objects created during your test.
* DEBUG_DEVTOOLS_ALLOCATIONS="verbose"
* This will print the allocation sites of all the JS objects created during your
* test. i.e. from which files and lines the objects have been created.
* In both cases, look for "DEVTOOLS ALLOCATION" in your terminal to see tracker's
* output.
*
* But you can also import it from your test script if you want to focus on one
* particular piece of code:
* const { allocationTracker } =
* require("devtools/shared/test-helpers/allocation-tracker");
* // Calling `allocationTracker` will immediately start recording allocations
* let tracker = allocationTracker();
*
* // Do something
*
* // If you want to log all the allocation sites, call this method:
* tracker.logAllocationLog();
* // Or, if you want to only print the number of objects being allocated, call this:
* tracker.logCount();
* // Once you are done, stop the tracker as it slow down execution a lot.
* tracker.stop();
*/
"use strict";
const MemoryReporter = Cc["@mozilla.org/memory-reporter-manager;1"].getService(
Ci.nsIMemoryReporterManager
);
const global = Cu.getGlobalForObject(this);
const { addDebuggerToGlobal } = ChromeUtils.importESModule(
{ global: "contextual" }
);
addDebuggerToGlobal(global);
/**
* Start recording JS object allocations.
*
* @param Object watchGlobal
* One global object to observe. Only allocation made from this global
* will be recorded.
* @param Boolean watchAllGlobals
* If true, allocations from everywhere are going to be recorded.
* @param Boolean watchAllGlobals
* If true, only allocations made from DevTools contexts are going to be recorded.
*/
exports.allocationTracker = function ({
watchGlobal,
watchAllGlobals,
watchDevToolsGlobals,
} = {}) {
dump("DEVTOOLS ALLOCATION: Start logging allocations\n");
let dbg = new global.Debugger();
// Enable allocation site tracking, to have the stack for each allocation
dbg.memory.trackingAllocationSites = true;
// Force saving *all* the allocation sites
dbg.memory.allocationSamplingProbability = 1.0;
// Bumps the default buffer size, which may prevent recording all the test allocations
dbg.memory.maxAllocationsLogLength = 5000000;
let acceptGlobal;
if (watchGlobal) {
acceptGlobal = () => false;
dbg.addDebuggee(watchGlobal);
} else if (watchAllGlobals) {
acceptGlobal = () => true;
} else if (watchDevToolsGlobals) {
// Only accept globals related to DevTools
acceptGlobal = g => {
// self-hosting-global crashes when trying to call unsafeDereference
if (g.class == "self-hosting-global") {
dump("TRACKER NEW GLOBAL: - : " + g.class + "\n");
return false;
}
let ref = g.unsafeDereference();
// If we are on a toolbox's iframe, typically each panel's iframe
// retrieve the toolbox iframe via window.top
if (g.class == "Window" && ref.top) {
ref = ref.top;
}
const location = Cu.getRealmLocation(ref);
let accept = !!location.match(/devtools/i);
// Also ignore the dedicated Sandbox used to spawn builtin-modules,
// as well as its internal ChromeDebugger Sandbox.
// We ignore the global used by the dedicated loader used to load
// the allocation-tracker module.
if (
ref == Cu.getGlobalForObject(builtinGlobal) ||
ref == Cu.getGlobalForObject(builtinGlobal.modules.ChromeDebugger)
) {
accept = false;
}
dump(
"TRACKER NEW GLOBAL: " + (accept ? "+" : "-") + " : " + location + "\n"
);
return accept;
};
}
// Watch all globals
if (watchAllGlobals || watchDevToolsGlobals) {
dbg.addAllGlobalsAsDebuggees();
for (const g of dbg.getDebuggees()) {
if (!acceptGlobal(g)) {
dbg.removeDebuggee(g);
}
}
}
// Remove this global to ignore all its object/JS
dbg.removeDebuggee(global);
// addAllGlobalsAsDebuggees won't automatically track new ones,
// so ensure tracking all new globals
dbg.onNewGlobalObject = function (g) {
if (acceptGlobal(g)) {
dbg.addDebuggee(g);
}
};
return {
get overflowed() {
return dbg.memory.allocationsLogOverflowed;
},
async startRecordingAllocations(debug_allocations) {
// Do a first pass of GC, to ensure all to-be-freed objects from the first run
// are really freed.
// We have to temporarily disable allocation-site recording in order to ensure
// freeing everything and especially avoid retaining objects in the allocation-log
// related to `drainAllocationLog` feature.
dbg.memory.allocationSamplingProbability = 0.0;
// Also force clearing the allocation log in order to prevent holding alive globals
// which have been destroyed before we start recording
this.flushAllocations();
await this.doGC();
dbg.memory.allocationSamplingProbability = 1.0;
// Measure the current process memory usage
const memory = this.getAllocatedMemory();
// Then, record how many objects were already allocated, which should not be declared
// as potential leaks. For ex, there is all the modules already loaded
// in the main DevTools loader.
const objects = this.stillAllocatedObjects();
// Flush the allocations so that the next call to logAllocationLog
// ignore allocations which happened before this call.
if (debug_allocations == "allocations") {
this.flushAllocations();
}
// Retrieve all allocation sites of all the objects already allocated.
// So that we can ignore them when we stop the record.
const allocations =
debug_allocations == "leaks" ? this.getAllAllocations() : null;
this.data = { memory, objects, allocations };
return this.data;
},
async stopRecordingAllocations(debug_allocations) {
// We have to flush the allocation log in order to prevent leaking some objects
// being hold in memory solely by their allocation-site (i.e. `SavedFrame` in `Debugger::allocationsLog`)
if (debug_allocations != "allocations") {
this.flushAllocations();
}
// In the content process we watch for all globals.
// Disable allocation record immediately, as we get some allocation reported by the allocation-tracker itself.
if (watchAllGlobals) {
dbg.memory.allocationSamplingProbability = 0.0;
}
// Before computing allocations, re-do some GCs in order to free all what is to-be-freed.
await this.doGC();
// If we are in the parent process, we watch only for devtools globals.
// So we can more safely assert that no allocation occured while doing the GCs.
// If means that the test we are recording is having pending operation which aren't properly recorded.
if (!watchAllGlobals) {
const allocations = dbg.memory.drainAllocationsLog();
if (allocations.length) {
this.logAllocationLog(
allocations,
"Allocation that happened during the GC"
);
console.error(
"Allocation happened during the GC. Are you waiting correctly before calling stopRecordingAllocations?"
);
}
}
const memory = this.getAllocatedMemory();
const objects = this.stillAllocatedObjects();
let leaks;
if (debug_allocations == "allocations") {
this.logAllocationLog();
} else if (debug_allocations == "leaks") {
leaks = this.logAllocationSitesDiff(this.data.allocations);
}
return {
objectsWithoutStack:
objects.objectsWithoutStack - this.data.objects.objectsWithoutStack,
objectsWithStack:
objects.objectsWithStack - this.data.objects.objectsWithStack,
memory: memory - this.data.memory,
leaks,
};
},
/**
* Return the collection of currently allocated JS Objects.
*
* This returns an object whose structure is documented in logAllocationSites.
*/
getAllAllocations() {
const sensus = dbg.memory.takeCensus({
breakdown: { by: "allocationStack" },
});
const sources = {};
for (const [k, v] of sensus.entries()) {
const src = k.source || "UNKNOWN";
const line = k.line || "?";
const count = v.count;
let item = sources[src];
if (!item) {
item = sources[src] = { count: 0, lines: {} };
}
item.count += count;
if (line != -1) {
if (!item.lines[line]) {
item.lines[line] = 0;
}
item.lines[line] += count;
}
}
return sources;
},
/**
* Substract count of `previousSources` from `newSources`.
* This help know which allocations where done between `previousSources` and `newSources` records,
* and, are still allocated.
*
* The structure of source objects is documented in logAllocationSites.
*/
sourcesDiff(previousSources, newSources) {
for (const src in previousSources) {
const previousItem = previousSources[src];
const item = newSources[src];
if (!item) {
continue;
}
item.count -= previousItem.count;
for (const line in previousItem.lines) {
const count = previousItem.lines[line];
if (line != -1) {
if (!item.lines[line]) {
continue;
}
item.lines[line] -= count;
}
}
}
},
/**
* Print to stdout data about all recorded allocations
*
* It prints an array of allocations per file, sorted by files allocating the most
* objects. And get detail of allocation per line.
*
* count: 210, // Total # of allocs for toolbox.js
* lines: [
* "10: 200", // toolbox.js allocation 200 objects on line 10
* "124: 10
* ]
* },
* count: 12,
* lines: [
* "20: 12",
* ]
* }]
*
* @param first Number
* Retrieve only the top $first script allocation the most
* objects
*/
logAllocationSites(message, sources, { first = 1000 } = {}) {
const allocationList = Object.entries(sources)
// Sort by number of total object
.sort(([, itemA], [, itemB]) => itemB.count - itemA.count)
// Keep only the first n-th sources, with the most allocations
.filter((_, i) => i < first)
.map(([src, item]) => {
const lines = [];
Object.entries(item.lines)
// Filter out lines where we only freed objects
.filter(([, count]) => count > 0)
.sort(([lineA, countA], [lineB, countB]) => {
if (countA != countB) {
return countB - countA;
}
return lineB - lineA;
})
.forEach(([line, count]) => {
// Compress the data to make it readable on stdout
lines.push(line + ": " + count);
});
return { src, count: item.count, lines };
})
// Filter out modules where we only freed objects
.filter(({ count }) => count > 0);
dump(
"DEVTOOLS ALLOCATION: " +
message +
":\n" +
JSON.stringify(allocationList, null, 2) +
"\n"
);
return allocationList;
},
/**
* This method requires a previous call to getAllAllocations
* and will print only the allocation sites which are still allocated.
* Usage:
* const previousSources = this.getAllAllocations();
* ... exercice something, which may leak ...
* this.logAllocationSitesDiff(previousSources);
*/
logAllocationSitesDiff(previousSources) {
const newSources = this.getAllAllocations();
this.sourcesDiff(previousSources, newSources);
return this.logAllocationSites("allocations which leaked", newSources);
},
/**
* Convert allocation structure coming out from Memory API's `drainAllocationsLog()`
* to source structure documented in logAllocationSites.
*/
allocationsToSources(allocations) {
const sources = {};
for (const alloc of allocations) {
const { frame } = alloc;
let src = "UNKNOWN";
let line = -1;
try {
if (frame) {
src = frame.source || "UNKNOWN";
line = frame.line || -1;
}
} catch (e) {
// For some frames accessing source throws
}
let item = sources[src];
if (!item) {
item = sources[src] = { count: 0, lines: {} };
}
item.count++;
if (line != -1) {
if (!item.lines[line]) {
item.lines[line] = 0;
}
item.lines[line]++;
}
}
return sources;
},
/**
* This method will log all the allocations that happened since the last call
* to this method -or- to `flushAllocations`.
* Reported allocations may have been freed.
* Use `logAllocationSitesDiff` to know what hasn't been freed.
*/
logAllocationLog(allocations, msg = "") {
if (!allocations) {
allocations = dbg.memory.drainAllocationsLog();
}
const sources = this.allocationsToSources(allocations);
return this.logAllocationSites(
msg
? msg
: "all allocations (which may be freed or are still allocated)",
sources
);
},
logCount() {
dump(
"DEVTOOLS ALLOCATION: Javascript object allocations: " +
this.countAllocations() +
"\n"
);
},
countAllocations() {
// Fetch all allocation sites from Debugger API
const allocations = dbg.memory.drainAllocationsLog();
return allocations.length;
},
/**
* Reset the allocation log, so that the next call to logAllocationLog/drainAllocationsLog
* will report all allocations which happened after this call to flushAllocations.
*/
flushAllocations() {
dbg.memory.drainAllocationsLog();
},
/**
* Compute the live count of object currently allocated.
*
* `objects` attribute will count all the objects,
* while `objectsWithNoStack` will report how many are missing allocation site/stack.
*/
stillAllocatedObjects() {
const sensus = dbg.memory.takeCensus({
breakdown: { by: "allocationStack" },
});
let objectsWithStack = 0;
let objectsWithoutStack = 0;
for (const [k, v] of sensus.entries()) {
// Objects with missing stack will all be keyed under "noStack" string,
// while all others will have a stack object as key.
if (k === "noStack") {
objectsWithoutStack += v.count;
} else {
objectsWithStack += v.count;
}
}
return { objectsWithStack, objectsWithoutStack };
},
/**
* Reports the amount of OS memory used by the current process.
*/
getAllocatedMemory() {
return MemoryReporter.residentUnique;
},
async doGC() {
// In order to get stable results, we really have to do 3 GC attempts
// *and* do wait for 1s between each GC.
const numCycles = 3;
for (let i = 0; i < numCycles; i++) {
Cu.forceGC();
Cu.forceCC();
await new Promise(resolve => Cu.schedulePreciseShrinkingGC(resolve));
// eslint-disable-next-line mozilla/no-arbitrary-setTimeout
await new Promise(resolve => setTimeout(resolve, 1000));
}
// Also call minimizeMemoryUsage as that's the only way to purge JIT cache.
// CachedIR objects (JIT related objects) are ultimately leading to keep
// all transient globals in memory. For some reason, when enabling trackingAllocationSites=true
// we compute stack traces (SavedFrame) for each object being allocated.
// This either create new CachedIR -or- force holding alive existing CachedIR
// and CachedIR itself hold strong references to the transient globals.
await new Promise(resolve => MemoryReporter.minimizeMemoryUsage(resolve));
},
/**
* Return the absolute file path to a memory snapshot.
* This is used to compute dominator trees in `traceObjects`.
*/
getSnapshotFile() {
return ChromeUtils.saveHeapSnapshot({ debugger: dbg });
},
/**
* Print information about why a list of objects are being held in memory.
*
* @param Array<NodeId> objects
* List of NodeId's of objects to debug. NodeIds can be retrieved
* via ChromeUtils.getObjectNodeId.
* @param String snapshotFile
* Absolute path to a Heap snapshot file retrieved via this.getSnapshotFile.
* This is used to trace content process objects. We have to record the snapshot
* from the content process, but can only read it from the parent process because
* of I/O restrictions in content processes.
*/
traceObjects(objects, snapshotFile) {
// There is no API to get the heap snapshot at runtime,
// the only way is to save it to disk and then load it from disk
if (!snapshotFile) {
snapshotFile = this.getSnapshotFile();
}
const snapshot = ChromeUtils.readHeapSnapshot(snapshotFile);
function getObjectClass(id) {
if (!id) {
return "<null>";
}
try {
let stack = [...snapshot.describeNode({ by: "allocationStack" }, id)];
let line;
if (stack) {
stack = stack.find(([src]) => src != "noStack");
if (stack) {
line = stack[0].line;
stack = stack[0].source;
if (stack) {
const pstack = stack;
stack = stack.match(/\/([^\/]+)$/);
if (stack) {
stack = stack[1];
} else {
stack = pstack;
}
} else {
stack = "no-source";
}
} else {
stack = "no-stack";
}
} else {
stack = "no-desc";
}
return (
Object.entries(
snapshot.describeNode({ by: "objectClass" }, id)
)[0][0] + (stack ? "@" + stack + ":" + line : "")
);
} catch (e) {
if (e.name == "NS_ERROR_ILLEGAL_VALUE") {
return "<not-in-memory-snapshot:is-from-untracked-global?>";
}
return "<invalid:" + id + ":" + e + ">";
}
}
function printPath(src, dst) {
let paths;
try {
paths = snapshot.computeShortestPaths(src, [dst], 10);
} catch (e) {}
if (paths && paths.has(dst)) {
let pathLength = Infinity;
for (const path of paths.get(dst)) {
// Only print the smaller paths.
// The longer ones will only repeat the smaller ones, with some extra edges.
if (path.length > pathLength) {
continue;
}
pathLength = path.length;
dump(
"- " +
path
.map(
({ predecessor, edge }) =>
getObjectClass(predecessor) + "." + edge
)
.join("\n \\--> ") +
"\n \\--> " +
getObjectClass(dst) +
"\n"
);
}
} else {
dump("NO-PATH\n");
}
}
const tree = snapshot.computeDominatorTree();
for (const objectNodeId of objects) {
dump(" # Tracing: " + getObjectClass(objectNodeId) + "\n");
// Print the path from the global object down to leaked object.
// This print the allocation site of each object which has a reference
// to another object, ultimately leading to our leaked object.
dump("### Path(s) from root:\n");
printPath(tree.root, objectNodeId);
/**
* This happens to be redundant with printPath, but printed the other way around.
*
// Print the dominators.
// i.e. from the leaked object, print all parent objects whichs
// keeps a reference to the previous object, up to a global object.
dump("### Dominators:\n");
let node = objectNodeId,
dump(" " + getObjectClass(node) + "\n");
while ((node = tree.getImmediateDominator(node))) {
dump(" ^-- " + getObjectClass(node) + "\n");
}
*/
/**
* In case you are not able to figure out what the object is.
* This will print all what it keeps allocated,
* kinds of list of attributes
*
dump("### Dominateds:\n");
node = objectNodeId,
dump(" " + getObjectClass(node) + "\n");
for (const n of tree.getImmediatelyDominated(objectNodeId)) {
dump(" --> " + getObjectClass(n) + "\n");
}
*/
}
},
stop() {
dump("DEVTOOLS ALLOCATION: Stop logging allocations\n");
dbg.onNewGlobalObject = undefined;
dbg.removeAllDebuggees();
dbg = null;
},
};
};