wait for two short reads before uncapping the max read size · qinheping/verify-rust-std@94105e8 (original) (raw)
`@@ -398,8 +398,7 @@ where
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`// - avoid passing large buffers to readers that always initialize the free capacity if they perform short reads (#23815, #23820)
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`// - pass large buffers to readers that do not initialize the spare capacity. this can amortize per-call overheads
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`// - and finally pass not-too-small and not-too-large buffers to Windows read APIs because they manage to suffer from both problems
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``
`-
// at the same time, i.e. small reads suffer from syscall overhead, all reads incur initialization cost
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``
`-
// proportional to buffer size (#110650)
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// at the same time, i.e. small reads suffer from syscall overhead, all reads incur costs proportional to buffer size (#110650)
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`//
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`pub(crate) fn default_read_to_end<R: Read + ?Sized>(
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`r: &mut R,
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`@@ -444,6 +443,8 @@ pub(crate) fn default_read_to_end<R: Read + ?Sized>(
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`}
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`}
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``
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let mut consecutive_short_reads = 0;
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`loop {
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`if buf.len() == buf.capacity() && buf.capacity() == start_cap {
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`// The buffer might be an exact fit. Let's read into a probe buffer
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`@@ -489,6 +490,12 @@ pub(crate) fn default_read_to_end<R: Read + ?Sized>(
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`return Ok(buf.len() - start_len);
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`}
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``
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if bytes_read < buf_len {
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consecutive_short_reads += 1;
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} else {
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consecutive_short_reads = 0;
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}
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`// store how much was initialized but not filled
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` initialized = unfilled_but_initialized;
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``
`@@ -503,7 +510,10 @@ pub(crate) fn default_read_to_end<R: Read + ?Sized>(
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`// The reader is returning short reads but it doesn't call ensure_init().
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`// In that case we no longer need to restrict read sizes to avoid
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`// initialization costs.
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`-
if !was_fully_initialized {
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// When reading from disk we usually don't get any short reads except at EOF.
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// So we wait for at least 2 short reads before uncapping the read buffer;
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// this helps with the Windows issue.
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if !was_fully_initialized && consecutive_short_reads > 1 {
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` max_read_size = usize::MAX;
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`}
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``