Fix "unexpected null" handling overlapping file changes #1083
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Summary: Fixes a crash where a race in overlapping file change processing could occasionally throw "unexpected null". Fixes facebook#1015 ## Root cause The problem logic is in some instrumentation code introduced in D40346848. `metro-file-map` batches changes using `setInterval(emitChange, 30)`. The instrumentation attempted to record the time of the first event in a given batch, and then "reset the clock" when the batch is emitted to the consumer. The problem occurred when an emit interval fell such that a non-empty `emitChange` occurred *during* the async `_processFile` step of a subsequent change. The first emit would reset the "start time" to `null`, and the second `emitChange` would fail at `nullthrows(eventStartTimestamp)`, because `eventStartTimestamp` is only set *before* `_processFile` starts (and only if already `null`). The (over)writing of `eventStartTimestamp` was flawed, because we don't know at the start of change processing that this event is going to be the start of a batch - this only becomes clear when an event is subsequently enqueued for emit after file processing. ## This diff This changes the recording of the start time such that we take a timestamp on every change, and record it as the batch start time on the creation of a new batch. We rearrange the various moving parts into a nullable object, so that "first event time" is tightly coupled to the batch it describes, and can never be `null` for a non-empty batch. ## Changelog ``` * **[Fix]:** Fix "unexpected null" crash when handling a batch of file changes. ``` Differential Revision: D49272782
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This pull request was exported from Phabricator. Differential Revision: D49272782 |
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Summary: Pull Request resolved: #1083 Fixes a crash where a race in overlapping file change processing could occasionally throw "unexpected null". Fixes #1015 ## Root cause The problem logic is in some instrumentation code introduced in D40346848. `metro-file-map` batches changes using `setInterval(emitChange, 30)`. The instrumentation attempted to record the time of the first event in a given batch, and then "reset the clock" when the batch is emitted to the consumer. The problem occurred when an emit interval fell such that a non-empty `emitChange` occurred *during* the async `_processFile` step of a subsequent change. The first emit would reset the "start time" to `null`, and the second `emitChange` would fail at `nullthrows(eventStartTimestamp)`, because `eventStartTimestamp` is only set *before* `_processFile` starts (and only if already `null`). The (over)writing of `eventStartTimestamp` was flawed, because we don't know at the start of change processing that this event is going to be the start of a batch - this only becomes clear when an event is subsequently enqueued for emit after file processing. ## This diff This changes the recording of the start time such that we take a timestamp on every change, and record it as the batch start time on the creation of a new batch. We rearrange the various moving parts into a nullable object, so that "first event time" is tightly coupled to the batch it describes, and can never be `null` for a non-empty batch. ## Changelog ``` * **[Fix]:** Fix "unexpected null" crash when handling a batch of file changes. ``` Reviewed By: huntie Differential Revision: D49272782 fbshipit-source-id: 8e1a4ebb6876fad982af3aa8a1922c6f14236040
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### Summary Metro server often crashes with ``` status-mobile/node_modules/nullthrows/nullthrows.js:9 throw error; ^ Error: Got unexpected null ``` This commit resolves metro to a commit where this specific issue was fixed. related PR in metro repo : facebook/metro#1083
robhogan
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Summary: Pull Request resolved: #1083 Fixes a crash where a race in overlapping file change processing could occasionally throw "unexpected null". Fixes #1015 ## Root cause The problem logic is in some instrumentation code introduced in D40346848. `metro-file-map` batches changes using `setInterval(emitChange, 30)`. The instrumentation attempted to record the time of the first event in a given batch, and then "reset the clock" when the batch is emitted to the consumer. The problem occurred when an emit interval fell such that a non-empty `emitChange` occurred *during* the async `_processFile` step of a subsequent change. The first emit would reset the "start time" to `null`, and the second `emitChange` would fail at `nullthrows(eventStartTimestamp)`, because `eventStartTimestamp` is only set *before* `_processFile` starts (and only if already `null`). The (over)writing of `eventStartTimestamp` was flawed, because we don't know at the start of change processing that this event is going to be the start of a batch - this only becomes clear when an event is subsequently enqueued for emit after file processing. ## This diff This changes the recording of the start time such that we take a timestamp on every change, and record it as the batch start time on the creation of a new batch. We rearrange the various moving parts into a nullable object, so that "first event time" is tightly coupled to the batch it describes, and can never be `null` for a non-empty batch. ## Changelog ``` * **[Fix]:** Fix "unexpected null" crash when handling a batch of file changes. ``` Reviewed By: huntie Differential Revision: D49272782 fbshipit-source-id: 8e1a4ebb6876fad982af3aa8a1922c6f14236040
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Summary:
Fixes a crash where a race in overlapping file change processing could occasionally throw "unexpected null".
Root cause
The problem logic is in some instrumentation code introduced in D40346848.
metro-file-mapbatches changes usingsetInterval(emitChange, 30). The instrumentation attempted to record the time of the first event in a given batch, and then "reset the clock" when the batch is emitted to the consumer.The problem occurred when an emit interval fell such that a non-empty
emitChangeoccurred during the async_processFilestep of a subsequent change. The first emit would reset the "start time" tonull, and the secondemitChangewould fail atnullthrows(eventStartTimestamp), becauseeventStartTimestampis only set before_processFilestarts (and only if alreadynull).The (over)writing of
eventStartTimestampwas flawed, because we don't know at the start of change processing that this event is going to be the start of a batch - this only becomes clear when an event is subsequently enqueued for emit after file processing.This diff
This changes the recording of the start time such that we take a timestamp on every change, and record it as the batch start time on the creation of a new batch. We rearrange the various moving parts into a nullable object, so that "first event time" is tightly coupled to the batch it describes, and can never be
nullfor a non-empty batch.Changelog
Differential Revision: D49272782