unix: check RLIMIT_AS and RLIMIT_DATA in uv_get_constrained_memory

Add uv__get_rlimit_max_memory() helper that checks RLIMIT_AS and
RLIMIT_DATA resource limits across all Unix platforms. This helper
returns the minimum of these rlimits if set.

Update all Unix platform implementations of uv_get_constrained_memory()
to use this helper, ensuring consistent handling of resource limits:
- Linux: combine cgroup limits with rlimits
- z/OS: combine RLIMIT_MEMLIMIT with rlimits
- Other Unix platforms: use rlimits (previously returned 0)

This provides a more accurate view of available memory when processes
have rlimit constraints in addition to platform-specific limits.

Related: https://github.com/JuliaLang/julia/pull/51656

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/unix/aix.c

@@ -396,7 +396,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/core.c

@@ -2149,3 +2149,30 @@ int uv__sock_reuseport(int fd) {
 
   return 0;
 }
+
+
+uint64_t uv__get_rlimit_max_memory(void) {
+  struct rlimit rl;
+  uint64_t result = 0;
+  uint64_t rlimit_value;
+
+#if defined(RLIMIT_AS)
+  /* Check RLIMIT_AS (virtual memory limit). */
+  if (getrlimit(RLIMIT_AS, &rl) == 0 && rl.rlim_cur != RLIM_INFINITY) {
+    rlimit_value = rl.rlim_cur;
+    if (result == 0 || rlimit_value < result)
+      result = rlimit_value;
+  }
+#endif
+
+#if defined(RLIMIT_DATA)
+  /* Check RLIMIT_DATA (data segment limit). */
+  if (getrlimit(RLIMIT_DATA, &rl) == 0 && rl.rlim_cur != RLIM_INFINITY) {
+    rlimit_value = rl.rlim_cur;
+    if (result == 0 || rlimit_value < result)
+      result = rlimit_value;
+  }
+#endif
+
+  return result;
+}

src/unix/cygwin.c

@@ -85,7 +85,7 @@ int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
 }
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 uint64_t uv_get_available_memory(void) {

src/unix/darwin.c

@@ -121,7 +121,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/freebsd.c

@@ -117,7 +117,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/haiku.c

@@ -80,7 +80,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/hurd.c

@@ -163,7 +163,7 @@ int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
 }
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/ibmi.c

@@ -245,7 +245,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/internal.h

@@ -377,6 +377,7 @@ int uv__signal_loop_fork(uv_loop_t* loop);
 
 /* platform specific */
 uint64_t uv__hrtime(uv_clocktype_t type);
+uint64_t uv__get_rlimit_max_memory(void);
 int uv__kqueue_init(uv_loop_t* loop);
 int uv__platform_loop_init(uv_loop_t* loop);
 void uv__platform_loop_delete(uv_loop_t* loop);

src/unix/linux.c

@@ -53,6 +53,7 @@
 #include <sys/sysmacros.h>
 #include <sys/types.h>
 #include <sys/utsname.h>
+#include <sys/resource.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -2217,11 +2218,21 @@ static uint64_t uv__get_cgroup_constrained_memory(char buf[static 1024]) {
 
 uint64_t uv_get_constrained_memory(void) {
   char buf[1024];
+  uint64_t cgroup_limit;
+  uint64_t rlimit_limit;
 
   if (uv__slurp("/proc/self/cgroup", buf, sizeof(buf)))
     return 0;
 
-  return uv__get_cgroup_constrained_memory(buf);
+  cgroup_limit = uv__get_cgroup_constrained_memory(buf);
+  rlimit_limit = uv__get_rlimit_max_memory();
+
+  /* Return the minimum of cgroup and rlimit constraints. */
+  if (cgroup_limit == 0)
+    return rlimit_limit;
+  if (rlimit_limit == 0)
+    return cgroup_limit;
+  return cgroup_limit < rlimit_limit ? cgroup_limit : rlimit_limit;
 }
 
 

src/unix/netbsd.c

@@ -127,7 +127,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/openbsd.c

@@ -135,7 +135,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/os390.c

@@ -188,12 +188,23 @@ uint64_t uv_get_total_memory(void) {
 
 uint64_t uv_get_constrained_memory(void) {
   struct rlimit rl;
+  uint64_t memlimit;
+  uint64_t rlimit_limit;
 
   /* RLIMIT_MEMLIMIT return value is in megabytes rather than bytes. */
-  if (getrlimit(RLIMIT_MEMLIMIT, &rl) == 0)
-    return rl.rlim_cur * 1024 * 1024;
+  memlimit = 0;
+  if (getrlimit(RLIMIT_MEMLIMIT, &rl) == 0 && rl.rlim_cur != RLIM_INFINITY)
+    memlimit = rl.rlim_cur * 1024 * 1024;
 
-  return 0; /* There is no memory limit set. */
+  /* Also check RLIMIT_AS and RLIMIT_DATA. */
+  rlimit_limit = uv__get_rlimit_max_memory();
+
+  /* Return the minimum of RLIMIT_MEMLIMIT and other rlimits. */
+  if (memlimit == 0)
+    return rlimit_limit;
+  if (rlimit_limit == 0)
+    return memlimit;
+  return memlimit < rlimit_limit ? memlimit : rlimit_limit;
 }
 
 

src/unix/qnx.c

@@ -118,7 +118,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;
+  return uv__get_rlimit_max_memory();
 }
 
 

src/unix/sunos.c

@@ -413,7 +413,7 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  return uv__get_rlimit_max_memory();
 }