From 6232d13f5321b87ddf12a1aa36b4545da45f173d Mon Sep 17 00:00:00 2001
From: Joel Klinghed <the_jk@spawned.biz>
Date: Wed, 17 Nov 2021 22:34:57 +0100
Subject: Travel3: Simple image and video display site

Reads the images and videos from filesystem and builds a site in
memroy.
---
 src/observer_list.hh | 148 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100644 src/observer_list.hh

(limited to 'src/observer_list.hh')

diff --git a/src/observer_list.hh b/src/observer_list.hh
new file mode 100644
index 0000000..86cdc03
--- /dev/null
+++ b/src/observer_list.hh
@@ -0,0 +1,148 @@
+#ifndef OBSERVER_LIST_HH
+#define OBSERVER_LIST_HH
+
+#include "common.hh"
+
+#include <algorithm>
+#include <vector>
+
+template<typename T>
+class ObserverList {
+public:
+  class iterator {
+  public:
+    iterator()
+      : list_(nullptr), index_(0), end_(0) {}
+
+    ~iterator() {
+      if (list_)
+        list_->release();
+    }
+
+    iterator(iterator const& it)
+      : list_(it.list_), index_(it.index_), end_(it.end_) {
+      if (list_) {
+        list_->aquire();
+        while (index_ < end_ && !list_->observers_[index_])
+          ++index_;
+      }
+    }
+
+    iterator& operator=(iterator const& it) {
+      if (list_ != it.list_) {
+        if (list_)
+          list_->release();
+        list_ = it.list_;
+        if (list_)
+          list_->aquire();
+      }
+      index_ = it.index_;
+      end_ = it.end_;
+      return *this;
+    }
+
+    explicit operator bool() {
+      return index_ < end_;
+    }
+
+    T& operator*() {
+      return *list_->observers_[index_];
+    }
+
+    T* operator->() {
+      return list_->observers_[index_];
+    }
+
+    iterator operator++(int) {
+      iterator ret(*this);
+      ++(*this);
+      return ret;
+    }
+
+    iterator& operator++() {
+      if (index_ < end_) {
+        do {
+          ++index_;
+        } while (index_ < end_ && !list_->observers_[index_]);
+      }
+      return *this;
+    }
+
+  private:
+    friend class ObserverList;
+
+    iterator(ObserverList* list, size_t index, size_t end)
+      : list_(list), index_(index), end_(end) {
+      list_->aquire();
+      while (index_ < end_ && !list_->observers_[index_])
+        ++index_;
+    }
+
+    ObserverList* list_;
+    size_t index_;
+    size_t end_;
+  };
+
+  ObserverList() = default;
+  ~ObserverList() {
+    assert(active_ == 0);
+  }
+
+  bool empty() const {
+    return observers_.empty();
+  }
+
+  void add(T* observer) {
+    assert(std::find(observers_.begin(), observers_.end(), observer)
+           == observers_.end());
+    observers_.push_back(observer);
+  }
+
+  void remove(T* observer) {
+    auto it = std::find(observers_.begin(), observers_.end(), observer);
+    if (it != observers_.end()) {
+      if (active_) {
+        *it = nullptr;
+        ++deleted_;
+      } else {
+        observers_.erase(it);
+      }
+    } else {
+      assert(false);
+    }
+  }
+
+  iterator notify() {
+    return iterator(this, 0, observers_.size());
+  }
+
+private:
+  void aquire() {
+    ++active_;
+  }
+
+  void release() {
+    assert(active_ > 0);
+    --active_;
+    if (active_ == 0 && deleted_)
+      cleanup();
+  }
+
+  void cleanup() {
+    size_t i = observers_.size();
+    while (deleted_ && i > 0) {
+      --i;
+      if (!observers_[i]) {
+        --deleted_;
+        observers_.erase(observers_.begin() + i);
+      }
+    }
+    assert(deleted_ == 0);
+  }
+
+  std::vector<T*> observers_;
+  unsigned active_{0};
+  unsigned deleted_{0};
+};
+
+#endif  // OBSERVER_LIST_HH
-- 
cgit v1.2.3-70-g09d2