Added IPCThreadState::blockUntilThreadAvailable() method.

Will be used by the system_server watchdog to monitor the
availability of binder threads in the process to handle
incoming IPC requests.

Bug: 19297165
Change-Id: I39175f3869ad14da5620fddb47f454e6e4ee2b25

include/binder/IPCThreadState.h

@@ -84,6 +84,10 @@ public:
     // the background.
     static  void                disableBackgroundScheduling(bool disable);
 
+            // Call blocks until the number of executing binder threads is less than
+            // the maximum number of binder threads threads allowed for this process.
+            void                blockUntilThreadAvailable();
+
 private:
                                 IPCThreadState();
                                 ~IPCThreadState();

include/binder/ProcessState.h

@@ -24,6 +24,8 @@
 
 #include <utils/threads.h>
 
+#include <pthread.h>
+
 // ---------------------------------------------------------------------------
 namespace android {
 
@@ -82,6 +84,14 @@ private:
             int                 mDriverFD;
             void*               mVMStart;
 
+            // Protects thread count variable below.
+            pthread_mutex_t     mThreadCountLock;
+            pthread_cond_t      mThreadCountDecrement;
+            // Number of binder threads current executing a command.
+            size_t              mExecutingThreadsCount;
+            // Maximum number for binder threads allowed for this process.
+            size_t              mMaxThreads;
+
     mutable Mutex               mLock;  // protects everything below.
 
             Vector<handle_entry>mHandleToObject;

libs/binder/IPCThreadState.cpp

@@ -399,6 +399,17 @@ void IPCThreadState::flushCommands()
     talkWithDriver(false);
 }
 
+void IPCThreadState::blockUntilThreadAvailable()
+{
+    pthread_mutex_lock(&mProcess->mThreadCountLock);
+    while (mProcess->mExecutingThreadsCount >= mProcess->mMaxThreads) {
+        ALOGW("Waiting for thread to be free. mExecutingThreadsCount=%i mMaxThreads=%i\n",
+                mProcess->mExecutingThreadsCount, mProcess->mMaxThreads);
+        pthread_cond_wait(&mProcess->mThreadCountDecrement, &mProcess->mThreadCountLock);
+    }
+    pthread_mutex_unlock(&mProcess->mThreadCountLock);
+}
+
 status_t IPCThreadState::getAndExecuteCommand()
 {
     status_t result;
@@ -414,8 +425,17 @@ status_t IPCThreadState::getAndExecuteCommand()
                  << getReturnString(cmd) << endl;
         }
 
+        pthread_mutex_lock(&mProcess->mThreadCountLock);
+        mProcess->mExecutingThreadsCount++;
+        pthread_mutex_unlock(&mProcess->mThreadCountLock);
+
         result = executeCommand(cmd);
 
+        pthread_mutex_lock(&mProcess->mThreadCountLock);
+        mProcess->mExecutingThreadsCount--;
+        pthread_cond_broadcast(&mProcess->mThreadCountDecrement);
+        pthread_mutex_unlock(&mProcess->mThreadCountLock);
+
         // After executing the command, ensure that the thread is returned to the
         // foreground cgroup before rejoining the pool.  The driver takes care of
         // restoring the priority, but doesn't do anything with cgroups so we

libs/binder/ProcessState.cpp

@@ -42,6 +42,7 @@
 #include <sys/stat.h>
 
 #define BINDER_VM_SIZE ((1*1024*1024) - (4096 *2))
+#define DEFAULT_MAX_BINDER_THREADS 15
 
 
 // ---------------------------------------------------------------------------
@@ -294,7 +295,9 @@ void ProcessState::spawnPooledThread(bool isMain)
 
 status_t ProcessState::setThreadPoolMaxThreadCount(size_t maxThreads) {
     status_t result = NO_ERROR;
-    if (ioctl(mDriverFD, BINDER_SET_MAX_THREADS, &maxThreads) == -1) {
+    if (ioctl(mDriverFD, BINDER_SET_MAX_THREADS, &maxThreads) != -1) {
+        mMaxThreads = maxThreads;
+    } else {
         result = -errno;
         ALOGE("Binder ioctl to set max threads failed: %s", strerror(-result));
     }
@@ -322,7 +325,7 @@ static int open_driver()
             close(fd);
             fd = -1;
         }
-        size_t maxThreads = 15;
+        size_t maxThreads = DEFAULT_MAX_BINDER_THREADS;
         result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);
         if (result == -1) {
             ALOGE("Binder ioctl to set max threads failed: %s", strerror(errno));
@@ -336,6 +339,10 @@ static int open_driver()
 ProcessState::ProcessState()
     : mDriverFD(open_driver())
     , mVMStart(MAP_FAILED)
+    , mThreadCountLock(PTHREAD_MUTEX_INITIALIZER)
+    , mThreadCountDecrement(PTHREAD_COND_INITIALIZER)
+    , mExecutingThreadsCount(0)
+    , mMaxThreads(DEFAULT_MAX_BINDER_THREADS)
     , mManagesContexts(false)
     , mBinderContextCheckFunc(NULL)
     , mBinderContextUserData(NULL)