binder: remove mutex from transaction processing loop

atomic ops are enough for the various count fields, we don't need a
completely consistent view of them.

Bug: 333946800
Test: atest --test-mapping frameworks/native/libs/binder/TEST_MAPPING
Change-Id: I01f55a36f7421e4955e2b0d3a6500b183573d765

1 files changed, 37 insertions, 39 deletions

diff --git a/libs/binder/IPCThreadState.cpp b/libs/binder/IPCThreadState.cpp
index ef96f803c3..ad20cfa11e 100644
--- a/libs/binder/IPCThreadState.cpp
+++ b/libs/binder/IPCThreadState.cpp
@@ -613,16 +613,20 @@ bool IPCThreadState::flushIfNeeded()
 
 void IPCThreadState::blockUntilThreadAvailable()
 {
-    pthread_mutex_lock(&mProcess->mThreadCountLock);
-    mProcess->mWaitingForThreads++;
-    while (mProcess->mExecutingThreadsCount >= mProcess->mMaxThreads) {
-        ALOGW("Waiting for thread to be free. mExecutingThreadsCount=%lu mMaxThreads=%lu\n",
-                static_cast<unsigned long>(mProcess->mExecutingThreadsCount),
-                static_cast<unsigned long>(mProcess->mMaxThreads));
-        pthread_cond_wait(&mProcess->mThreadCountDecrement, &mProcess->mThreadCountLock);
-    }
-    mProcess->mWaitingForThreads--;
-    pthread_mutex_unlock(&mProcess->mThreadCountLock);
+    std::unique_lock lock_guard_(mProcess->mOnThreadAvailableLock);
+    mProcess->mOnThreadAvailableWaiting++;
+    mProcess->mOnThreadAvailableCondVar.wait(lock_guard_, [&] {
+        size_t max = mProcess->mMaxThreads;
+        size_t cur = mProcess->mExecutingThreadsCount;
+        if (cur < max) {
+            return true;
+        }
+        ALOGW("Waiting for thread to be free. mExecutingThreadsCount=%" PRId64
+              " mMaxThreads=%" PRId64 "\n",
+              cur, max);
+        return false;
+    });
+    mProcess->mOnThreadAvailableWaiting--;
 }
 
 status_t IPCThreadState::getAndExecuteCommand()
@@ -642,34 +646,33 @@ status_t IPCThreadState::getAndExecuteCommand()
             ALOGI("%s", message.c_str());
         }
 
-        pthread_mutex_lock(&mProcess->mThreadCountLock);
-        mProcess->mExecutingThreadsCount++;
-        if (mProcess->mExecutingThreadsCount >= mProcess->mMaxThreads &&
-                mProcess->mStarvationStartTimeMs == 0) {
-            mProcess->mStarvationStartTimeMs = uptimeMillis();
+        size_t newThreadsCount = mProcess->mExecutingThreadsCount.fetch_add(1) + 1;
+        if (newThreadsCount >= mProcess->mMaxThreads) {
+            int64_t expected = 0;
+            mProcess->mStarvationStartTimeMs.compare_exchange_strong(expected, uptimeMillis());
         }
-        pthread_mutex_unlock(&mProcess->mThreadCountLock);
 
         result = executeCommand(cmd);
 
-        pthread_mutex_lock(&mProcess->mThreadCountLock);
-        mProcess->mExecutingThreadsCount--;
-        if (mProcess->mExecutingThreadsCount < mProcess->mMaxThreads &&
-                mProcess->mStarvationStartTimeMs != 0) {
-            int64_t starvationTimeMs = uptimeMillis() - mProcess->mStarvationStartTimeMs;
-            if (starvationTimeMs > 100) {
-                ALOGE("binder thread pool (%zu threads) starved for %" PRId64 " ms",
-                      mProcess->mMaxThreads, starvationTimeMs);
+        size_t maxThreads = mProcess->mMaxThreads;
+        newThreadsCount = mProcess->mExecutingThreadsCount.fetch_sub(1) - 1;
+        if (newThreadsCount < maxThreads) {
+            size_t starvationStartTimeMs = mProcess->mStarvationStartTimeMs.exchange(0);
+            if (starvationStartTimeMs != 0) {
+                int64_t starvationTimeMs = uptimeMillis() - starvationStartTimeMs;
+                if (starvationTimeMs > 100) {
+                    ALOGE("binder thread pool (%zu threads) starved for %" PRId64 " ms", maxThreads,
+                          starvationTimeMs);
+                }
             }
-            mProcess->mStarvationStartTimeMs = 0;
         }
 
         // Cond broadcast can be expensive, so don't send it every time a binder
         // call is processed. b/168806193
-        if (mProcess->mWaitingForThreads > 0) {
-            pthread_cond_broadcast(&mProcess->mThreadCountDecrement);
+        if (mProcess->mOnThreadAvailableWaiting > 0) {
+            std::lock_guard lock_guard_(mProcess->mOnThreadAvailableLock);
+            mProcess->mOnThreadAvailableCondVar.notify_all();
         }
-        pthread_mutex_unlock(&mProcess->mThreadCountLock);
     }
 
     return result;
@@ -727,10 +730,9 @@ void IPCThreadState::processPostWriteDerefs()
 
 void IPCThreadState::joinThreadPool(bool isMain)
 {
-    LOG_THREADPOOL("**** THREAD %p (PID %d) IS JOINING THE THREAD POOL\n", (void*)pthread_self(), getpid());
-    pthread_mutex_lock(&mProcess->mThreadCountLock);
+    LOG_THREADPOOL("**** THREAD %p (PID %d) IS JOINING THE THREAD POOL\n", (void*)pthread_self(),
+                   getpid());
     mProcess->mCurrentThreads++;
-    pthread_mutex_unlock(&mProcess->mThreadCountLock);
     mOut.writeInt32(isMain ? BC_ENTER_LOOPER : BC_REGISTER_LOOPER);
 
     mIsLooper = true;
@@ -758,13 +760,11 @@ void IPCThreadState::joinThreadPool(bool isMain)
     mOut.writeInt32(BC_EXIT_LOOPER);
     mIsLooper = false;
     talkWithDriver(false);
-    pthread_mutex_lock(&mProcess->mThreadCountLock);
-    LOG_ALWAYS_FATAL_IF(mProcess->mCurrentThreads == 0,
-                        "Threadpool thread count = 0. Thread cannot exist and exit in empty "
-                        "threadpool\n"
+    size_t oldCount = mProcess->mCurrentThreads.fetch_sub(1);
+    LOG_ALWAYS_FATAL_IF(oldCount == 0,
+                        "Threadpool thread count underflowed. Thread cannot exist and exit in "
+                        "empty threadpool\n"
                         "Misconfiguration. Increase threadpool max threads configuration\n");
-    mProcess->mCurrentThreads--;
-    pthread_mutex_unlock(&mProcess->mThreadCountLock);
 }
 
 status_t IPCThreadState::setupPolling(int* fd)
@@ -776,9 +776,7 @@ status_t IPCThreadState::setupPolling(int* fd)
     mOut.writeInt32(BC_ENTER_LOOPER);
     flushCommands();
     *fd = mProcess->mDriverFD;
-    pthread_mutex_lock(&mProcess->mThreadCountLock);
     mProcess->mCurrentThreads++;
-    pthread_mutex_unlock(&mProcess->mThreadCountLock);
     return 0;
 }