civodul pushed a commit to branch main
in repository guile.
commit 7b7340b2d9ad6c9e34a784555e6d70acbaf0e545
Author: Olivier Dion <olivier.d...@polymtl.ca>
AuthorDate: Tue Feb 18 20:40:41 2025 -0500
Warn about mutation of ‘environ’ when multi-threaded.
This is an amendment to 84bf84032208e21d20ad13f3033d4fca3a512014.
The warning was only emitted for calling `environ', even if only reading
and no mutation occurred.
However, it is correct to read the environment in a multi-threaded
process. It is however unsafe to mutate it.
The same logic also applies to `putenv'.
* libguile/posix.c
(maybe_warn_about_environ_mutation): New private procedure ...
(scm_environ): ... called here when mutating the environment ...
(scm_putenv): ... and here.
* NEWS: Update.
Signed-off-by: Ludovic Courtès <l...@gnu.org>
---
NEWS | 2 ++
libguile/posix.c | 31 +++++++++++++++++++------------
2 files changed, 21 insertions(+), 12 deletions(-)
diff --git a/NEWS b/NEWS
index ff4c977de..e7641c008 100644
--- a/NEWS
+++ b/NEWS
@@ -86,6 +86,8 @@ every line in a file.
in turn, would trigger warnings from 'primitive-fork' and 'environ'
suggesting they are being called in a multi-threaded context, when in
fact user code did not create any thread.
+** Calling 'environ' without arguments in a multi-threaded program is OK
+ This used to trigger a warning, unduly.
Changes in 3.0.10 (since 3.0.9)
diff --git a/libguile/posix.c b/libguile/posix.c
index 61b5523af..dde77b8ee 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -1705,6 +1705,19 @@ SCM_DEFINE (scm_uname, "uname", 0, 0, 0,
#undef FUNC_NAME
#endif /* HAVE_UNAME */
+static void
+maybe_warn_about_environ_mutation (void)
+{
+ /* Mutating `environ' directly in a multi-threaded program is
+ undefined behavior. */
+ if (scm_ilength (scm_all_threads ()) != 1)
+ scm_display
+ (scm_from_latin1_string
+ ("warning: mutating the process environment while multiple threads are
running;\n"
+ " further behavior unspecified.\n"),
+ scm_current_warning_port ());
+}
+
SCM_DEFINE (scm_environ, "environ", 0, 1, 0,
(SCM env),
"If @var{env} is omitted, return the current environment (in the\n"
@@ -1716,22 +1729,13 @@ SCM_DEFINE (scm_environ, "environ", 0, 1, 0,
"then the return value is unspecified.")
#define FUNC_NAME s_scm_environ
{
- /* Accessing `environ' directly in a multi-threaded program is
- undefined behavior since at anytime it could point to anything else
- while reading it. Not only that, but all accesses are protected by
- an internal mutex of libc. Thus, it is only truly safe to modify
- the environment directly in a single-threaded program. */
- if (scm_ilength (scm_all_threads ()) != 1)
- scm_display
- (scm_from_latin1_string
- ("warning: call to environ while multiple threads are running;\n"
- " further behavior unspecified.\n"),
- scm_current_warning_port ());
-
if (SCM_UNBNDP (env))
return scm_makfromstrs (-1, environ);
else
{
+ /* Mutating the environment in a multi-threaded program is hazardous. */
+ maybe_warn_about_environ_mutation ();
+
/* Arrange to not use GC-allocated storage for what goes into
'environ' as libc might reallocate it behind our back. */
#if HAVE_CLEARENV
@@ -1951,6 +1955,9 @@ SCM_DEFINE (scm_putenv, "putenv", 1, 0, 0,
int rv;
char *c_str = scm_to_locale_string (str);
+ /* Mutating the environment in a multi-threaded program is hazardous. */
+ maybe_warn_about_environ_mutation ();
+
/* Leave C_STR in the environment. */
/* Gnulib's `putenv' module honors the semantics described above. */
