Fixes for SkRWBuffer

Do not call SkBufferHead::validate in SkROBuffer's destructor, which
may be called in a separate thread from SkRWBuffer::append. validate()
reads SkBufferBlock::fUsed, and append() writes to it, resulting in
a data race.

Update some comments to be more clear about how it is safe to use
these classes across threads.

Test the readers in separate threads.

In addition, make sure it is safe to create a reader even when no
data has been appended. Add tests for this case.

Mark a parameter to SkBufferHead::validate() as const, reflecting
its use.

BUG=chromium:601578
BUG=chromium:605479

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1871953002

Review URL: https://codereview.chromium.org/1871953002

1 files changed, 53 insertions, 3 deletions

diff --git a/tests/DataRefTest.cpp b/tests/DataRefTest.cpp
index 002abcbe89..03f66c5b04 100644
--- a/tests/DataRefTest.cpp
+++ b/tests/DataRefTest.cpp
@@ -245,7 +245,7 @@ static void check_abcs(skiatest::Reporter* reporter, const char buffer[], size_t
     }
 }
 
-// stream should contains an integral number of copies of gABC.
+// stream should contain an integral number of copies of gABC.
 static void check_alphabet_stream(skiatest::Reporter* reporter, SkStream* stream) {
     REPORTER_ASSERT(reporter, stream->hasLength());
     size_t size = stream->getLength();
@@ -284,6 +284,8 @@ static void check_alphabet_buffer(skiatest::Reporter* reporter, const SkROBuffer
     check_abcs(reporter, storage.get(), size);
 }
 
+#include "SkTaskGroup.h"
+
 DEF_TEST(RWBuffer, reporter) {
     // Knowing that the default capacity is 4096, choose N large enough so we force it to use
     // multiple buffers internally.
@@ -301,6 +303,7 @@ DEF_TEST(RWBuffer, reporter) {
         REPORTER_ASSERT(reporter, N*26 == buffer.size());
     }
 
+    // Verify that although the SkRWBuffer's destructor has run, the readers are still valid.
     for (int i = 0; i < N; ++i) {
         REPORTER_ASSERT(reporter, (i + 1) * 26U == readers[i]->size());
         check_alphabet_buffer(reporter, readers[i]);
@@ -310,6 +313,35 @@ DEF_TEST(RWBuffer, reporter) {
     }
 }
 
+DEF_TEST(RWBuffer_threaded, reporter) {
+    // Knowing that the default capacity is 4096, choose N large enough so we force it to use
+    // multiple buffers internally.
+    const int N = 1000;
+    SkTaskGroup tasks;
+    SkRWBuffer buffer;
+    for (int i = 0; i < N; ++i) {
+        buffer.append(gABC, 26);
+        sk_sp<SkROBuffer> reader = sk_sp<SkROBuffer>(buffer.newRBufferSnapshot());
+        SkStream* stream = buffer.newStreamSnapshot();
+        REPORTER_ASSERT(reporter, reader->size() == buffer.size());
+        REPORTER_ASSERT(reporter, stream->getLength() == buffer.size());
+
+        // reader's copy constructor will ref the SkROBuffer, which will be unreffed
+        // when the task ends.
+        // Ownership of stream is passed to the task, which will delete it.
+        tasks.add([reporter, i, reader, stream] {
+            REPORTER_ASSERT(reporter, (i + 1) * 26U == reader->size());
+            REPORTER_ASSERT(reporter, stream->getLength() == reader->size());
+            check_alphabet_buffer(reporter, reader.get());
+            check_alphabet_stream(reporter, stream);
+            REPORTER_ASSERT(reporter, stream->rewind());
+            delete stream;
+        });
+    }
+    REPORTER_ASSERT(reporter, N*26 == buffer.size());
+    tasks.wait();
+}
+
 // Tests that it is safe to call SkROBuffer::Iter::size() when exhausted.
 DEF_TEST(RWBuffer_size, r) {
     SkRWBuffer buffer;
@@ -325,9 +357,27 @@ DEF_TEST(RWBuffer_size, r) {
     REPORTER_ASSERT(r, 0 == iter.size());
 }
 
-// Tests that it is safe to destruct an SkRWBuffer without appending
-// anything to it.
+// Tests that operations (including the destructor) are safe on an SkRWBuffer
+// without any data appended.
 DEF_TEST(RWBuffer_noAppend, r) {
     SkRWBuffer buffer;
     REPORTER_ASSERT(r, 0 == buffer.size());
+
+    sk_sp<SkROBuffer> roBuffer = sk_sp<SkROBuffer>(buffer.newRBufferSnapshot());
+    REPORTER_ASSERT(r, roBuffer);
+    if (roBuffer) {
+        REPORTER_ASSERT(r, roBuffer->size() == 0);
+        SkROBuffer::Iter iter(roBuffer.get());
+        REPORTER_ASSERT(r, iter.size() == 0);
+        REPORTER_ASSERT(r, !iter.data());
+        REPORTER_ASSERT(r, !iter.next());
+    }
+
+    SkAutoTDelete<SkStream> stream(buffer.newStreamSnapshot());
+    REPORTER_ASSERT(r, stream);
+    if (stream) {
+        REPORTER_ASSERT(r, stream->hasLength());
+        REPORTER_ASSERT(r, stream->getLength() == 0);
+        REPORTER_ASSERT(r, stream->skip(10) == 0);
+    }
 }