# HG changeset patch
# User Alain Leufroy
# Date 1576872099 -3600
#      Fri Dec 20 21:01:39 2019 +0100
# Node ID 305ef1b4bb16ddfc4bded0d88ceb693c5c943000
# Parent  036e3ee2ce42fa89809fccd142009c30db98d392
limit number of async processes using `config.PRCESSES_NB`

diff --git a/lairucrem/config.py b/lairucrem/config.py
--- a/lairucrem/config.py
+++ b/lairucrem/config.py
@@ -1,3 +1,5 @@
+import asyncio
+import multiprocessing
 import re
 from pathlib import Path
 
@@ -514,12 +516,23 @@
 
 KEYBINDINGS = []
 
+# Optimal: > 6
+PROCESSES_NB = multiprocessing.cpu_count() - 1
+
 
 def has_mouse_keybindings():
     return 'mouse' in KEYBINDINGS
 
 
+PROCESSES_SEMAPHORE = None
+
+
 # Load user defined configuration
 CONFIG_FILE_PATH = Path('~/.config/lairucrem/config.py').expanduser()
 if CONFIG_FILE_PATH.exists():
     exec(CONFIG_FILE_PATH.read_text())
+
+
+if PROCESSES_SEMAPHORE is None:
+    # Do not overwrite PROCESSES_SEMAPHORE set from the user's config file.
+    PROCESSES_SEMAPHORE = asyncio.Semaphore(PROCESSES_NB + 1)
diff --git a/lairucrem/controler.py b/lairucrem/controler.py
--- a/lairucrem/controler.py
+++ b/lairucrem/controler.py
@@ -106,11 +106,12 @@
     async def _wait(self):
         await super()._wait()
         first = True
-        async for widget in self:
-            if first:
-                self.clear(full=True)
-                first = False
-            self.append(widget)
+        async with config.PROCESSES_SEMAPHORE:
+            async for widget in self:
+                if first:
+                    self.clear(full=True)
+                    first = False
+                self.append(widget)
         if first:               # nothing fetched
             self.clear(full=True)
         urwid.emit_signal(self, 'completed')
@@ -629,6 +630,19 @@
         self._diff.filename = filename
         self._diffstat.filename = filename
 
+    async def _wait(self):
+        # Load task is specific order to ensure that prefered sections
+        # appears quickly (PROCESSES_SEMAPHORE may delay a few of
+        # them).
+        await asyncio.gather(
+            self._diff.wait(),
+            self._summary.wait(),
+            self._description.wait(),
+            self._diffstat.wait(),
+            self._summaryextra.wait(),
+        )
+        urwid.emit_signal(self, 'completed')
+
 
 class patchlistbox(
         mixin.filterable_listbox,
@@ -771,12 +785,13 @@
     async def _grep_revset(self, pattern):
         self._grep_pattern = pattern
         csets = defaultdict(set)
-        async for line in process.hg('grep', '--all', '-l', pattern):
-            try:
-                data = dict(parse_colored_line(line))
-            except ValueError:
-                pass
-            csets[data['grep.rev']].add(data['grep.filename'])
+        with HG_SEMAPHORE:
+            async for line in process.hg('grep', '--all', '-l', pattern):
+                try:
+                    data = dict(parse_colored_line(line))
+                except ValueError:
+                    pass
+                csets[data['grep.rev']].add(data['grep.filename'])
         revset = ' or '.join(csets)
         return f'({revset})'
 
diff --git a/lairucrem/process.py b/lairucrem/process.py
--- a/lairucrem/process.py
+++ b/lairucrem/process.py
@@ -31,6 +31,7 @@
         msg = cmd + '\n\n' + msg
         raise OSError(proc.returncode, msg)
 
+
 class hg:
     """Async generator yielding mercurial command outputs.
 
@@ -191,9 +192,10 @@
     """Execute an Hg command in plain mode and return overall results."""
     env = os.environ.copy()
     env['HGPLAIN'] = '1'
-    hgproc = hg(*cmd, env=env)
-    try:
-        return ''.join([line async for line in hgproc])
-    except asyncio.CancelledError:
-        await hgproc.kill()
-    return ''
+    async with config.PROCESSES_SEMAPHORE:
+        hgproc = hg(*cmd, env=env)
+        try:
+            return ''.join([line async for line in hgproc])
+        except asyncio.CancelledError:
+            await hgproc.kill()
+        return ''