From 1b179455fce9aaf8ce8d1f28f0e552efdee2b7f9 Mon Sep 17 00:00:00 2001
From: "Paul \"LeoNerd\" Evans" <paul@matrix.org>
Date: Wed, 19 Oct 2016 15:34:38 +0100
Subject: [PATCH] Guard registration of process-wide metrics by existence of
 the requisite /proc entries

---
 synapse/metrics/__init__.py | 85 ++++++++++++++++++++-----------------
 1 file changed, 45 insertions(+), 40 deletions(-)

diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index a79fb026d4..323328061a 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -115,6 +115,10 @@ def render_all():
 TICKS_PER_SEC = 100
 BYTES_PER_PAGE = 4096
 
+HAVE_PROC_STAT = os.path.exists("/proc/stat")
+HAVE_PROC_SELF_STAT = os.path.exists("/proc/self/stat")
+HAVE_PROC_SELF_LIMITS = os.path.exists("/proc/self/limits")
+
 rusage = None
 stats = None
 fd_counts = None
@@ -122,13 +126,11 @@ fd_counts = None
 # In order to report process_start_time_seconds we need to know the machine's
 # boot time, because the value in /proc/self/stat is relative to this
 boot_time = None
-try:
+if HAVE_PROC_STAT:
     with open("/proc/stat") as _procstat:
         for line in _procstat:
             if line.startswith("btime "):
                 boot_time = int(line.split()[1])
-except IOError:
-    pass
 
 TYPES = {
     stat.S_IFSOCK: "SOCK",
@@ -144,11 +146,12 @@ def update_resource_metrics():
     global rusage
     rusage = getrusage(RUSAGE_SELF)
 
-    global stats
-    with open("/proc/self/stat") as s:
-        line = s.read()
-        # line is PID (command) more stats go here ...
-        stats = line.split(") ", 1)[1].split(" ")
+    if HAVE_PROC_SELF_STAT:
+        global stats
+        with open("/proc/self/stat") as s:
+            line = s.read()
+            # line is PID (command) more stats go here ...
+            stats = line.split(") ", 1)[1].split(" ")
 
     global fd_counts
     fd_counts = _process_fds()
@@ -195,43 +198,45 @@ get_metrics_for("process").register_callback("fds", _process_fds, labels=["type"
 ## New prometheus-standard metric names
 process_metrics = get_metrics_for("process");
 
-process_metrics.register_callback(
-    "cpu_user_seconds_total", lambda: float(stats[11]) / TICKS_PER_SEC
-)
-process_metrics.register_callback(
-    "cpu_system_seconds_total", lambda: float(stats[12]) / TICKS_PER_SEC
-)
-process_metrics.register_callback(
-    "cpu_seconds_total", lambda: (float(stats[11]) + float(stats[12])) / TICKS_PER_SEC
-)
+if HAVE_PROC_SELF_STAT:
+    process_metrics.register_callback(
+        "cpu_user_seconds_total", lambda: float(stats[11]) / TICKS_PER_SEC
+    )
+    process_metrics.register_callback(
+        "cpu_system_seconds_total", lambda: float(stats[12]) / TICKS_PER_SEC
+    )
+    process_metrics.register_callback(
+        "cpu_seconds_total", lambda: (float(stats[11]) + float(stats[12])) / TICKS_PER_SEC
+    )
 
-process_metrics.register_callback(
-    "virtual_memory_bytes", lambda: int(stats[20])
-)
-process_metrics.register_callback(
-    "resident_memory_bytes", lambda: int(stats[21]) * BYTES_PER_PAGE
-)
+    process_metrics.register_callback(
+        "virtual_memory_bytes", lambda: int(stats[20])
+    )
+    process_metrics.register_callback(
+        "resident_memory_bytes", lambda: int(stats[21]) * BYTES_PER_PAGE
+    )
 
-process_metrics.register_callback(
-    "open_fds", lambda: sum(fd_counts.values())
-)
+    process_metrics.register_callback(
+        "open_fds", lambda: sum(fd_counts.values())
+    )
 
-def _get_max_fds():
-    with open("/proc/self/limits") as limits:
-        for line in limits:
-            if not line.startswith("Max open files "):
-                continue
-            # Line is  Max open files  $SOFT  $HARD
-            return int(line.split()[3])
-    return None
+    process_metrics.register_callback(
+        "start_time_seconds", lambda: boot_time + int(stats[19]) / TICKS_PER_SEC
+    )
 
-process_metrics.register_callback(
-    "max_fds", lambda: _get_max_fds()
-)
+if HAVE_PROC_SELF_LIMITS:
+    def _get_max_fds():
+        with open("/proc/self/limits") as limits:
+            for line in limits:
+                if not line.startswith("Max open files "):
+                    continue
+                # Line is  Max open files  $SOFT  $HARD
+                return int(line.split()[3])
+        return None
 
-process_metrics.register_callback(
-    "start_time_seconds", lambda: boot_time + int(stats[19]) / TICKS_PER_SEC
-)
+    process_metrics.register_callback(
+        "max_fds", lambda: _get_max_fds()
+    )
 
 reactor_metrics = get_metrics_for("reactor")
 tick_time = reactor_metrics.register_distribution("tick_time")