Have DumpPool return futures

Have DumpPool return futures when tasks are enqueued, instead of
having users register their task with a string. This change has the
following benefits:

* Simplifies DumpPool since it no longer needs to keep the map of
  strings to futures.

* Allows adding a set of tasks to DumpPool that might not be known at
  build time. For example, we can add a bunch of tasks from a vector,
  without needing to generate arbitrary strings for them.

* Reduces the ability to misuse DumpPool. Before this change, the user
  had to come up with strings representing each task, and needed to
  know a task with said name existed. This change moves it from being a
  runtime error to being a compile time one.

Test: atest dumpstate_smoke_test

Change-Id: Ic6c1a983b049e5236ac596e8af200a21c07ac31b
diff --git a/cmds/dumpstate/DumpPool.cpp b/cmds/dumpstate/DumpPool.cpp
index c2c8a72..4d3a67b 100644
--- a/cmds/dumpstate/DumpPool.cpp
+++ b/cmds/dumpstate/DumpPool.cpp
@@ -33,6 +33,20 @@
 
 const std::string DumpPool::PREFIX_TMPFILE_NAME = "dump-tmp.";
 
+
+void WaitForTask(std::future<std::string> future, const std::string& title, int out_fd) {
+    DurationReporter duration_reporter("Wait for " + title, true);
+
+    std::string result = future.get();
+    if (result.empty()) {
+        return;
+    }
+    DumpFileToFd(out_fd, title, result);
+    if (unlink(result.c_str())) {
+        MYLOGE("Failed to unlink (%s): %s\n", result.c_str(), strerror(errno));
+    }
+}
+
 DumpPool::DumpPool(const std::string& tmp_root) : tmp_root_(tmp_root), shutdown_(false),
         log_duration_(true) {
     assert(!tmp_root.empty());
@@ -40,31 +54,10 @@
 }
 
 DumpPool::~DumpPool() {
-    shutdown();
-}
-
-void DumpPool::start(int thread_counts) {
-    assert(thread_counts > 0);
-    assert(threads_.empty());
-    if (thread_counts > MAX_THREAD_COUNT) {
-        thread_counts = MAX_THREAD_COUNT;
-    }
-    MYLOGI("Start thread pool:%d", thread_counts);
-    shutdown_ = false;
-    for (int i = 0; i < thread_counts; i++) {
-        threads_.emplace_back(std::thread([=]() {
-            setThreadName(pthread_self(), i + 1);
-            loop();
-        }));
-    }
-}
-
-void DumpPool::shutdown() {
     std::unique_lock lock(lock_);
     if (shutdown_ || threads_.empty()) {
         return;
     }
-    futures_map_.clear();
     while (!tasks_.empty()) tasks_.pop();
 
     shutdown_ = true;
@@ -76,27 +69,22 @@
     }
     threads_.clear();
     deleteTempFiles(tmp_root_);
-    MYLOGI("shutdown thread pool");
+    MYLOGI("shutdown thread pool\n");
 }
 
-void DumpPool::waitForTask(const std::string& task_name, const std::string& title,
-        int out_fd) {
-    DurationReporter duration_reporter("Wait for " + task_name, true);
-    auto iterator = futures_map_.find(task_name);
-    if (iterator == futures_map_.end()) {
-        MYLOGW("Task %s does not exist", task_name.c_str());
-        return;
+void DumpPool::start(int thread_counts) {
+    assert(thread_counts > 0);
+    assert(threads_.empty());
+    if (thread_counts > MAX_THREAD_COUNT) {
+        thread_counts = MAX_THREAD_COUNT;
     }
-    Future future = iterator->second;
-    futures_map_.erase(iterator);
-
-    std::string result = future.get();
-    if (result.empty()) {
-        return;
-    }
-    DumpFileToFd(out_fd, title, result);
-    if (unlink(result.c_str())) {
-        MYLOGE("Failed to unlink (%s): %s\n", result.c_str(), strerror(errno));
+    MYLOGI("Start thread pool:%d\n", thread_counts);
+    shutdown_ = false;
+    for (int i = 0; i < thread_counts; i++) {
+        threads_.emplace_back(std::thread([=]() {
+            setThreadName(pthread_self(), i + 1);
+            loop();
+        }));
     }
 }