问题
For some reason, the object won't output until the sleep command is done.
[pscustomobject]@{message = 'hi'}; sleep 5
Here's another example. You won't see the output until the loop finishes.
foreach ($i in 1..60) {
if ($i -eq 1) { [pscustomobject]@{message = $i} }
sleep 1
}
I guess you have to output at least 2 objects to see anything? ¯\_(ツ)_/¯ After 15 seconds, you see both objects.
foreach ($i in 1..60) {
if ($i -eq 1 -or $i -eq 15) { [pscustomobject]@{message = $i} }
sleep 1
}
Or output enough properties (> 4) to implicitly call format-list instead of format-table. Format-table is the problem. This comes out right away.
[pscustomobject]@{a=1; b=2; c=3; d=4; e=5}; sleep 10
I wonder if a parameter to format-table could be added like -NoWait.
Known object types with format files containing column widths don't have this problem.
foreach ($i in 1..60) {
if ($i -eq 1) { get-process powershell }
sleep 1
}
Or objects that default to format-custom:
foreach ($i in 1..60) {
if ($i -eq 1) { get-date }
sleep 1
}
回答1:
tl;dr
If a command's output results in automatic tabular display (implicit
Format-Table), display output can situationally be delayed for up to 300 ms. (see below for why and when), which can have two unexpected effects:As in the question, a subsequent
Start-Sleepsubmitted before the delay has elapsed further delays output for (at least) the duration of the sleep - it effectively suspends completing the 300 ms. wait.A subsequent
Write-HostorOut-Hostcall can produce output that unexpectedly comes first.
You can force synchronous display output by piping the command to
Out-Hostor toFormat-Tableexplicitly (or any of the otherFormat-*cmdlets).- However, doing so means producing for-display output only, which means you lose the ability to (meaningfully) capture or relay the command's output.
# The Out-Host forces instant display, before sleeping starts.
# However, use of Out-Host means you can't capture the output.
[pscustomobject] @{message = 'hi'} | Out-Host; sleep 5
The behavior is explained by the infamous PSv5+ asynchronous behavior of implicitly applied Format-Table output: For data types without predefined formatting data that have 4 or fewer properties (which is what auto-selects table display), it waits for up to 300 msecs. before displaying output, in an effort to determine suitable column widths.
If you use Start-Sleep before that period has elapsed, you suspend waiting for as long as you're sleeping.
Output objects that happen not to trigger implicit Format-Table formatting are not affected, however:
# Immediate output, before sleeping ends:
# Out-of-band formatting of a .NET primitive.
PS> 1; Start-Sleep 5
# Implicit Format-*List* formatting due to having 5+ properties.
PS> [pscustomobject]@{a=1; b=2; c=3; d=4; e=5}; sleep 10
By contrast, because your command's output is an object with just 1 property and its type ([pscustomobject]) has no predefined formatting data associated with it, it triggers implicit Format-Table formatting and therefore exhibits the problem.
In short: The following command outputs are affected, because they select implicit Format-Table output while lacking predefined column widths, necessitating the delay:
objects whose type happens to have 4 or fewer properties
if those types have no associated predefined formatting data (see about_Format.ps1xml), which is generally true for
[pscustomobject]instances.- Additionally, but far less commonly, types with formatting data that default to table view but don't have column widths predefined, are also affected (e.g., the System.Guid type instances that
New-Guidoutputs).
- Additionally, but far less commonly, types with formatting data that default to table view but don't have column widths predefined, are also affected (e.g., the System.Guid type instances that
Types without formatting data that have 5 or more properties default to implicitly applied Format-List, where, due to line-by-line output, there's no need to determine useful column widths, and therefore no delay.
Note that this is only a display problem, and that if the command is captured or sent to a pipeline the data is immediately output (though the command won't finish overall until the Start-Sleep period has elapsed):
# The ForEach-Object command's script block receives the [pscustomobject]
# instance right away (and itself prints it *immediately* to the display,
# due to outputting a *string* (which never triggers the asynchronous behavior).
& { [pscustomobject]@{message = 'hi'}; sleep 5 } | ForEach-Object { "[$_]" }
While there are several ways to force synchronous (immediate) display output, they all change the fundamental behavior of the command:
# Piping to Out-Host:
# Directly prints to the *display* (host).
# No way for a caller to capture the result or for processing
# the result in a pipeline.
[pscustomobject]@{message = 'hi'} | Out-Host; sleep 5
# Using Write-Host:
# Prints directly to the *display* (host) by default.
# While it *is* possible to capture the result via output stream 6.
# the information stream (6> file.txt), that output:
# * is invariably converted to *strings*
# * and the string representation does *not* use the friendly default
# output formatting; instead, the objects are stringified with simple
# [psobject.].ToString() calls, which results in a much less friendly
# representation.
Write-Host ([pscustomobject]@{message = 'hi'}); sleep 5
# Piping to a Format-* cmdlet explicitly:
# While this does write to the success-output stream (stream number 1),
# as the command would by default, what is written isn't the original
# objects, but *formatting instructions*, which are useless for further
# programmatic processing.
# However, for redirecting the output to a file with Out-File or >
# this makes no difference, because they convert the formatting instructions
# to the strings you would see on the screen by default.
# By contrast, using Set-Content or any other cmdlet that expects actual data
# would not work meaningfully.
[pscustomobject]@{message = 'hi'} | Format-Table; sleep 5
回答2:
Pipe your custom object to the Out-Host cmdlet:
[pscustomobject]@{message = 'hi'} | Out-Host; sleep 5
When you use the Out-Host cmdlet, you are immediately displaying the results to the host. Without it, the object is output to the pipeline which is not returned until after the Start-Sleep cmdlet.
回答3:
Output less than 5 properties, and format-table implicitly runs. Format-table will wait an indefinite amount of time for the second object, before displaying the first object. This is for object types (like pscustomobject) without an xml file that define a default table view.
# no output for 5 seconds
&{get-date
sleep 5
get-date} | format-table
DisplayHint DateTime Date Day DayOfWeek DayOfYear Hour Kind Millisecond Minute
----------- -------- ---- --- --------- --------- ---- ---- ----------- ------
DateTime Saturday, February 8, 2020 10:24:48 AM 2/8/2020 12:00:00 AM 8 Saturday 39 10 Local 618 24
DateTime Saturday, February 8, 2020 10:24:53 AM 2/8/2020 12:00:00 AM 8 Saturday 39 10 Local 892 24
Compare with format-list:
& {get-date
sleep 5
get-date} | format-list
DisplayHint : DateTime
Date : 2/8/2020 12:00:00 AM
Day : 8
DayOfWeek : Saturday
DayOfYear : 39
Hour : 20
Kind : Local
Millisecond : 408
Minute : 37
Month : 2
Second : 18
Ticks : 637167910384087860
TimeOfDay : 20:37:18.4087860
Year : 2020
DateTime : Saturday, February 8, 2020 8:37:18 PM
DisplayHint : DateTime
Date : 2/8/2020 12:00:00 AM
Day : 8
DayOfWeek : Saturday
DayOfYear : 39
Hour : 20
Kind : Local
Millisecond : 662
Minute : 37
Month : 2
Second : 23
Ticks : 637167910436622480
TimeOfDay : 20:37:23.6622480
Year : 2020
DateTime : Saturday, February 8, 2020 8:37:23 PM
来源：https://stackoverflow.com/questions/59330539/weird-delay-of-the-output-of-an-object-when-followed-by-start-sleep-or-until-sc