Add fiber-print-limit command

Summary: Limits number of fibers printed for each FiberManager.

Reviewed By: yfeldblum

Differential Revision: D4432488

fbshipit-source-id: 1791c2bfe6d5b0c2f54142dc068b473fd72f5d5d

folly/fibers/README.md

@@ -497,6 +497,11 @@ $<span class="mi">4</span> <span class="o">=</span> <span class="nc" data-symbol
   <span class="o">&#125;</span>
 <span class="o">&#125;</span></pre></div>
 
+<p><tt>fiber-print-limit</tt> command can be used to change the maximum number of fibers printed for a <tt>fibers::FiberManager</tt> (default value is 100).</p>
+
+<div class="remarkup-code-block" data-code-lang="php"><pre class="remarkup-code"><span class="o">(</span><span class="no">gdb</span><span class="o">)</span> <span class="no">fiber</span><span class="o">-</span><span class="no">print</span><span class="o">-</span><span class="no">limit</span> <span class="mi">10</span>
+<span class="k">New</span> <span class="nc" data-symbol-name="fiber">fiber</span> <span class="no">limit</span> <span class="k">for</span> <span class="no">FiberManager</span> <span class="no">printer</span> <span class="no">set</span> <span class="no">to</span> <span class="mi">10</span></pre></div>
+
 <h3 id="printing-a-fiber-task">Printing a fiber-task <a href="#printing-a-fiber-task" class="headerLink">#</a></h3>
 
 <p>Given a pointer to a <tt>fibers::Fiber</tt>, which is running some fiber-task, you can get its current state:</p>

folly/fibers/scripts/gdb.py

@@ -58,6 +58,8 @@ class FiberPrinter:
 class FiberManagerPrinter:
     """Print a folly::fibers::Fiber"""
 
+    fiber_print_limit = 100
+
     def __init__(self, fm):
         self.fm = fm
 
@@ -68,7 +70,13 @@ class FiberManagerPrinter:
 
         active_fibers = collections.OrderedDict()
 
+        fiber_count = 0
+
         while fiber_hook != all_fibers.address:
+            if fiber_count == FiberManagerPrinter.fiber_print_limit:
+                active_fibers["..."] = "..."
+                break
+
             fiber = fiber_hook.cast(gdb.lookup_type("int64_t"))
             fiber = fiber - gdb.parse_and_eval(
                 "(int64_t)&folly::fibers::Fiber::globalListHook_")
@@ -80,6 +88,8 @@ class FiberManagerPrinter:
 
             fiber_hook = fiber_hook.dereference()['next_']
 
+            fiber_count = fiber_count + 1
+
         return active_fibers.items()
 
     def to_string(self):
@@ -89,6 +99,20 @@ class FiberManagerPrinter:
         return "folly::fibers::FiberManager"
 
 
+class FiberPrintLimitCommand(gdb.Command):
+    def __init__(self):
+        super(FiberPrintLimitCommand, self).__init__(
+            "fiber-print-limit", gdb.COMMAND_USER)
+
+    def invoke(self, arg, from_tty):
+        if not arg:
+            print("New limit has to be passed to 'fiber_print_limit' command")
+            return
+        FiberManagerPrinter.fiber_print_limit = int(arg)
+        print("New fiber limit for FiberManager printer set to " +
+              str(FiberManagerPrinter.fiber_print_limit))
+
+
 class FrameId(object):
     def __init__(self, sp, pc):
         self.sp = sp
@@ -281,6 +305,7 @@ def build_pretty_printer():
 def load():
     gdb.printing.register_pretty_printer(gdb, build_pretty_printer())
     gdb.xmethod.register_xmethod_matcher(gdb, FiberXMethodMatcher())
+    FiberPrintLimitCommand()
     FiberActivateCommand()
     FiberDeactivateCommand()
     Shortcut("get_fiber_manager_map_evb", get_fiber_manager_map_evb)