manual: Add note to process.texi about MT-process fork (Bug 30159)
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Build for i686
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Commit Message
The forked child of an MT-process may only call AS-safe functions.
---
manual/process.texi | 6 ++++++
1 file changed, 6 insertions(+)
Comments
* Carlos O'Donell via Libc-alpha:
> The forked child of an MT-process may only call AS-safe functions.
> ---
> manual/process.texi | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/manual/process.texi b/manual/process.texi
> index 9307379194..dfdf0923b4 100644
> --- a/manual/process.texi
> +++ b/manual/process.texi
> @@ -316,6 +316,12 @@ The child doesn't inherit alarms set by the parent process.
> The set of pending signals (@pxref{Delivery of Signal}) for the child
> process is cleared. (The child process inherits its mask of blocked
> signals and signal actions from the parent process.)
> +
> +@item
> +In the case of a multi-threaded parent, the child process may only
> +safely call asynchronous-signal-safe functions until the process is
> +replaced with a call to an @code{exec} family function.
We support calling malloc after fork as an extension. For example,
calling opendir after fork to find file descriptors in /proc/self/fd is
fairly common.
Perhaps add:
As an extension relative to POSIX, @theglibc{} supports calling
@code{malloc} and other allocation functions after @code{fork}. This
only applies to the standard @code{malloc}. Whether this extension is
supported by replacement @code{malloc} implementations depends on the
replacement. @xref{Replacing malloc}.
Thanks,
Florian
On 2/23/23 16:32, Florian Weimer wrote:
> * Carlos O'Donell via Libc-alpha:
>
>> The forked child of an MT-process may only call AS-safe functions.
>> ---
>> manual/process.texi | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/manual/process.texi b/manual/process.texi
>> index 9307379194..dfdf0923b4 100644
>> --- a/manual/process.texi
>> +++ b/manual/process.texi
>> @@ -316,6 +316,12 @@ The child doesn't inherit alarms set by the parent process.
>> The set of pending signals (@pxref{Delivery of Signal}) for the child
>> process is cleared. (The child process inherits its mask of blocked
>> signals and signal actions from the parent process.)
>> +
>> +@item
>> +In the case of a multi-threaded parent, the child process may only
>> +safely call asynchronous-signal-safe functions until the process is
>> +replaced with a call to an @code{exec} family function.
>
> We support calling malloc after fork as an extension. For example,
> calling opendir after fork to find file descriptors in /proc/self/fd is
> fairly common.
We support calling a lot of things in reality, but I didn't want to over commit
with this change to the manual. I like your narrowly worded addition.
> Perhaps add:
>
> As an extension relative to POSIX, @theglibc{} supports calling
> @code{malloc} and other allocation functions after @code{fork}. This
> only applies to the standard @code{malloc}. Whether this extension is
> supported by replacement @code{malloc} implementations depends on the
> replacement. @xref{Replacing malloc}.
v2 posted:
https://patchwork.sourceware.org/project/glibc/patch/20230223223728.423748-1-carlos@redhat.com/
Checked pdf/html/texi builds and the xref and macros look good.
@@ -316,6 +316,12 @@ The child doesn't inherit alarms set by the parent process.
The set of pending signals (@pxref{Delivery of Signal}) for the child
process is cleared. (The child process inherits its mask of blocked
signals and signal actions from the parent process.)
+
+@item
+In the case of a multi-threaded parent, the child process may only
+safely call asynchronous-signal-safe functions until the process is
+replaced with a call to an @code{exec} family function.
+
@end itemize
@deftypefun pid_t _Fork (void)