expose observers to python, add multiple observers per observable

Summary: observer framework can now be used in python + a small writeup of how to use it.  this is D6035393 with a fix for ct-scan

Reviewed By: salexspb

Differential Revision: D6066380

fbshipit-source-id: 896c4c580d4387240b81ac2dbbc43db51d4bfeb9

2 files changed, 10 insertions, 3 deletions

diff --git a/caffe2/share/contrib/observers/perf_observer.cc b/caffe2/share/contrib/observers/perf_observer.cc
index 000883b3f7..ad8ce8388b 100644
--- a/caffe2/share/contrib/observers/perf_observer.cc
+++ b/caffe2/share/contrib/observers/perf_observer.cc
@@ -50,7 +50,8 @@ bool PerfNetObserver::Start() {
        whenever we measure operator delay */
     const auto& operators = subject_->GetOperators();
     for (auto* op : operators) {
-      op->SetObserver(caffe2::make_unique<PerfOperatorObserver>(op, this));
+      observerMap_[op] = op->AttachObserver(
+          caffe2::make_unique<PerfOperatorObserver>(op, this));
     }
   }
 
@@ -72,7 +73,7 @@ bool PerfNetObserver::Stop() {
     for (int idx = 0; idx < operators.size(); ++idx) {
       const auto* op = operators[idx];
       auto name = getObserverName(op, idx);
-      double delay = static_cast<const PerfOperatorObserver*>(op->GetObserver())
+      double delay = static_cast<const PerfOperatorObserver*>(observerMap_[op])
                          ->getMilliseconds();
       std::pair<std::string, double> name_delay_pair = {name, delay};
       operator_delays.push_back(name_delay_pair);
@@ -82,8 +83,9 @@ bool PerfNetObserver::Stop() {
     /* clear all operator delay after use so that we don't spent time
        collecting the operator delay info in later runs */
     for (auto* op : operators) {
-      op->RemoveObserver();
+      op->DetachObserver(observerMap_[op]);
     }
+    observerMap_.clear();
   }
   return true;
 }
diff --git a/caffe2/share/contrib/observers/perf_observer.h b/caffe2/share/contrib/observers/perf_observer.h
index 7ac4ed21dd..770d5371e4 100644
--- a/caffe2/share/contrib/observers/perf_observer.h
+++ b/caffe2/share/contrib/observers/perf_observer.h
@@ -1,8 +1,11 @@
 #pragma once
 
 #include "caffe2/core/net.h"
+#include "caffe2/core/observer.h"
 #include "caffe2/core/timer.h"
 
+#include <unordered_map>
+
 namespace caffe2 {
 
 class PerfNetObserver : public NetObserver {
@@ -28,6 +31,8 @@ class PerfNetObserver : public NetObserver {
   };
   LogType logType_;
   unsigned int numRuns_;
+  std::unordered_map<const OperatorBase*, const ObserverBase<OperatorBase>*>
+      observerMap_;
 
   caffe2::Timer timer_;
 };