forked from mirrors/gecko-dev
82 lines
2.9 KiB
Markdown
82 lines
2.9 KiB
Markdown
# Basic operations
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## Opening the Memory tool
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Before Firefox 50, the Memory tool is not enabled by default. To enable
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it, open the developer tool settings, and check the "Memory" box under
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"Default Firefox Developer Tools":
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<iframe width="595" height="325" src="https://www.youtube.com/embed/qi-0CoCOXw" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"></iframe>
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From Firefox 50 onwards, the Memory tool is enabled by default.
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## Taking a heap snapshot
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To take a snapshot of the heap, click the "Take snapshot" button, or
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the camera icon on the left:
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The snapshot will occupy the large pane on the right-hand side. On the
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left, you'll see an entry for the new snapshot, including its
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timestamp, size, and controls to save or clear this snapshot:
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## Clearing a snapshot
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To remove a snapshot, click the "X" icon:
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## Saving and loading snapshots
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If you close the Memory tool, all unsaved snapshots will be discarded.
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To save a snapshot click "Save":
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You'll be prompted for a name and location, and the file will be saved
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with an `.fxsnapshot` extension.
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To load a snapshot from an existing `.fxsnapshot` file, click the import
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button, which looks like a rectangle with an arrow rising from it
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(before Firefox 49, this button was labeled with the text
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"Import\...\"):
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You'll be prompted to find a snapshot file on disk.
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## Comparing snapshots
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Starting in Firefox 45, you can diff two heap snapshots. The diff shows
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you where memory was allocated or freed between the two snapshots.
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To create a diff, click the button that looks like a Venn diagram next
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to the camera icon (before Firefox 47, this looked like a \"+/-\" icon):
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You'll be prompted to select the snapshot to use as a baseline, then
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the snapshot to compare. The tool then shows you the differences between
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the two snapshots:
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<iframe width="595" height="325" src="https://www.youtube.com/embed/3Ow-mdK6b2M" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"></iframe>
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::: {.note}
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When you're looking at a comparison, you can't use the Dominators view
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or the Tree Map view.
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:::
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## Recording call stacks
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The Memory tool can tell you exactly where in your code you are
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allocating memory. However, recording this information has a run-time
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cost, so you must ask the tool to record memory calls *before* the
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memory is allocated, if you want to see memory call sites in the
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snapshot. To do this, check "Record call stacks" (before Firefox 49
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this was labeled "Record allocation stacks"):
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