gltrace: Add support for tracing running applications.

Currently, to activate OpenGL tracing, an application has to be
start with --opengl-trace option (or have a debug prop set).

This CL adds support for tracing an application which may already
be running. This is implemented as follows:
    - DDMS initiates a JDWP message to the VM indicating that
      opengl traces be enabled.
    - When that message is received, a flag is set that indicates
      that tracing should be enabled.
    - The trace flag is checked during every eglSwap() operation,
      and if it finds that tracing should be active and it isn't,
      then it starts the tracing component.

Change-Id: I3347fe89fc06c7404d7aa9360f4b21e5bf36ebcb

2 files changed, 88 insertions, 13 deletions

diff --git a/opengl/libs/GLES_trace/DESIGN.txt b/opengl/libs/GLES_trace/DESIGN.txt
index a189e1d..72a2e15 100644
--- a/opengl/libs/GLES_trace/DESIGN.txt
+++ b/opengl/libs/GLES_trace/DESIGN.txt
@@ -9,9 +9,6 @@ Code Runtime Behavior:
     control whether tracing should be enabled for a certain process. If tracing is enabled, this
     calls GLTrace_start() to start the trace server.
     
-    Note that initEglTraceLevel() is also called from early_egl_init(), but that happens in the
-    context of the zygote, so that invocation has no effect.
-    
     egl_display_t::initialize() then calls setGLHooksThreadSpecific() where we set the thread
     specific gl_hooks structure to point to the trace implementation. From this point on, every
     GLES call is redirected to the trace implementation.
@@ -30,6 +27,37 @@ Code Runtime Behavior:
     to explore if a more graceful method of stopping the application, or detaching tracing from the
     application is required.
 
+
+Enabling tracing while the application is running:
+
+    In order to allow tracing of an already running application, we allow DdmServer to enable
+    OpenGL tracing. In such a case, the application already has its GL hooks set up to point to the
+    real GL implementation, and we need to switch them to point to the trace implementation.
+
+    This is achieved by checking whether tracing should be enabled at every eglSwap call.
+    (Note: We were already checking for tracing at every eglSwap, the only change now is that
+    the tracing could actually be ON/OFF at runtime - earlier it was set once and never changed).
+
+    If eglSwap detects that tracing should be enabled now, then it performs the following steps:
+        - switch the gl hooks to point to the trace implementation.
+        - call trace eglMakeCurrent to indicate that there is now a new context that is current.
+        - continue on with tracing the eglSwap call.
+    This switches the hooks to point to the trace implementation only for the current context.
+    But the other contexts have their gl hooks updated when they perform eglMakeCurrent.
+
+    The GLTrace version of eglMakeCurrent now has to be updated to allow switching to a context
+    it may not know of. In such a case, it creates a context matching the version that it is now
+    switching to.
+
+Disabling tracing:
+
+    We disable tracing under two conditions:
+        - stop tracing request from DdmServer
+        - gltrace transport gets disconnected from the host.
+    In either case, both actions simply disable the tracing flag. The current context gets its
+    gl hooks restored in the next eglSwap, and the other traced contexts get their gl hooks
+    restored when they perform a eglMakeCurrent.
+
 Code Structure:
 
     glestrace.h declares all the hooks exposed by libglestrace. These are used by EGL/egl.cpp and
diff --git a/opengl/libs/GLES_trace/src/gltrace_eglapi.cpp b/opengl/libs/GLES_trace/src/gltrace_eglapi.cpp
index 9698bf9..512d562 100644
--- a/opengl/libs/GLES_trace/src/gltrace_eglapi.cpp
+++ b/opengl/libs/GLES_trace/src/gltrace_eglapi.cpp
@@ -33,6 +33,9 @@ using gltrace::GLTraceState;
 using gltrace::GLTraceContext;
 using gltrace::TCPStream;
 
+static pthread_mutex_t sGlTraceStateLock = PTHREAD_MUTEX_INITIALIZER;
+
+static int sGlTraceInProgress;
 static GLTraceState *sGLTraceState;
 static pthread_t sReceiveThreadId;
 
@@ -105,33 +108,66 @@ static void *commandReceiveTask(void *arg) {
     return NULL;
 }
 
-void GLTrace_start() {
-    char udsName[PROPERTY_VALUE_MAX];
+/**
+ * Starts Trace Server and waits for connection from the host.
+ * Returns -1 in case of connection error, 0 otherwise.
+ */
+int GLTrace_start() {
+    int status = 0;
+    int clientSocket = -1;
+    TCPStream *stream = NULL;
+
+    pthread_mutex_lock(&sGlTraceStateLock);
 
+    if (sGlTraceInProgress) {
+        goto done;
+    }
+
+    char udsName[PROPERTY_VALUE_MAX];
     property_get("debug.egl.debug_portname", udsName, "gltrace");
-    int clientSocket = gltrace::acceptClientConnection(udsName);
+    clientSocket = gltrace::acceptClientConnection(udsName);
     if (clientSocket < 0) {
-        ALOGE("Error creating GLTrace server socket. Quitting application.");
-        exit(-1);
+        ALOGE("Error creating GLTrace server socket. Tracing disabled.");
+        status = -1;
+        goto done;
     }
 
+    sGlTraceInProgress = 1;
+
     // create communication channel to the host
-    TCPStream *stream = new TCPStream(clientSocket);
+    stream = new TCPStream(clientSocket);
 
     // initialize tracing state
     sGLTraceState = new GLTraceState(stream);
 
     pthread_create(&sReceiveThreadId, NULL, commandReceiveTask, sGLTraceState);
+
+done:
+    pthread_mutex_unlock(&sGlTraceStateLock);
+    return status;
 }
 
 void GLTrace_stop() {
-    delete sGLTraceState;
-    sGLTraceState = NULL;
+    pthread_mutex_lock(&sGlTraceStateLock);
+
+    if (sGlTraceInProgress) {
+        sGlTraceInProgress = 0;
+        delete sGLTraceState;
+        sGLTraceState = NULL;
+    }
+
+    pthread_mutex_unlock(&sGlTraceStateLock);
 }
 
 void GLTrace_eglCreateContext(int version, EGLContext c) {
+    pthread_mutex_lock(&sGlTraceStateLock);
+    GLTraceState *state = sGLTraceState;
+    pthread_mutex_unlock(&sGlTraceStateLock);
+
+    if (state == NULL) return;
+
     // update trace state for new EGL context
-    GLTraceContext *traceContext = sGLTraceState->createTraceContext(version, c);
+    GLTraceContext *traceContext = state->createTraceContext(version, c);
     gltrace::setupTraceContextThreadSpecific(traceContext);
 
     // trace command through to the host
@@ -139,8 +175,19 @@ void GLTrace_eglCreateContext(int version, EGLContext c) {
 }
 
 void GLTrace_eglMakeCurrent(const unsigned version, gl_hooks_t *hooks, EGLContext c) {
+    pthread_mutex_lock(&sGlTraceStateLock);
+    GLTraceState *state = sGLTraceState;
+    pthread_mutex_unlock(&sGlTraceStateLock);
+
+    if (state == NULL) return;
+
     // setup per context state
-    GLTraceContext *traceContext = sGLTraceState->getTraceContext(c);
+    GLTraceContext *traceContext = state->getTraceContext(c);
+    if (traceContext == NULL) {
+        GLTrace_eglCreateContext(version, c);
+        traceContext = state->getTraceContext(c);
+    }
+
     traceContext->hooks = hooks;
     gltrace::setupTraceContextThreadSpecific(traceContext);